Overview of hand infections

INTRODUCTION — Hand infections are much more common compared with infections at other limb sites and have the potential to significantly impair hand function. Hand infections are classified as superficial or deep. An untreated superficial hand infection can progress and become a deep hand infection, which is a surgical emergency. Prompt evaluation and proper treatment of hand infections are important and can mean the difference between an excellent outcome and permanent disability.

The basic principles of evaluating and treating hand infections and considerations for specific hand infections are reviewed. An overview of the evaluation of hand pain is discussed separately. (See "History and examination of the adult with hand pain".)

ANATOMY AND CLASSIFICATION

Superficial versus deep hand infections — Superficial hand infections are generally limited to the skin and subcutaneous tissues. Superficial hand infections include cellulitis, lymphangitis, paronychia, pulp space infections, herpetic whitlow, subcutaneous abscess, and web space abscess. These infections typically present with a history of minor trauma, are associated with few systemic symptoms, are relatively easy to diagnose, and are amenable to a trial of close nonsurgical treatment, especially in the early phase prior to abscess formation. (See 'Superficial hand infections' below.)

An untreated superficial hand infection can progress to involve deeper tissue planes and become a deep hand infection.

Deep hand infections involve the deeper structures including tendon sheaths, tendons, potential synovial spaces, intermuscular planes, bone, and joints. Deep hand infections include synovial space infections, deep fascial space infections, septic arthritis, and necrotizing fasciitis. (See 'Deep hand infections' below.)

Compared with superficial hand infections, deep hand infections are difficult to diagnose, especially in the early stages, and often result from hematogenous spread without any history of trauma. They are associated with more pain, swelling, limitation of motion, and systemic symptoms (eg, fever and tachycardia).

CLINICAL FEATURES — The initial evaluation and management of hand infection includes a focused history and examination and often involves laboratory evaluation and imaging.

History — A focused medical history should determine the possible source of infection, history of progress of the infection, the immune status of the patient, and any relevant past medical history. Most patients with acute hand infections are healthy and active young adults who put off treatment for minor trauma. More severe infections can be seen in patients with impaired immune status.

●Symptoms – The onset of hand pain, any loss of hand function, fever and/or chills, and any spontaneous drainage should be documented. Severe throbbing pain is suggestive of an abscess in a confined space. (See 'Deep hand infections' below.)

A rapid deterioration in general condition suggests severe infections like necrotizing fasciitis. (See 'Necrotizing fasciitis' below.)

●Prior injury – Any prior hand injury from splinters, bites, and needle sticks and any prior attempts at drainage either by the patient or other clinicians should be noted.

●Hand dominance – The patient's dominant hand should be documented.

●Occupation – The patient's occupation may increase their exposure to certain infectious agents. An animal handler may be prone to bite wounds that may become infected with organisms typical for the involved species (eg, Pasteurella). A rose gardener is at risk for infection with Sporothrix through the introduction of spores through a cut or puncture wound in the skin. Certain professions are more prone to chronic paronychia. As an example, dishwashers are likely to develop Candida infections, whereas a person employed in a tropical fish aquarium is more likely to develop a Mycobacterium infection after a hand injury. (See 'Bite wounds' below and 'Superficial hand infections' below.)

●Immune status – Host factors that lower immune status increase the risk of significant morbidity from hand infections (eg, diabetes mellitus, chronic kidney disease, malignancy).

●Prior treatment – Documentation of how the infection has been managed can help determine next steps in the treatment plan.

Patients should be questioned about any similar lesions elsewhere suggesting hematogenous multifocal presentation or similar episodes in the past and whether they were ever treated for inflammatory arthropathies like rheumatoid arthritis or gout. This medical history combined with clinical examination and investigations can help differentiate between an infectious and an inflammatory process. (See 'Differential diagnosis' below.)

Physical examination — On physical examination, vital signs should be taken and recorded, and any fever noted. The entire upper extremity should be exposed for a systematic examination. The hand and wrist are examined for the presence of swelling, deformity, open wounds, alignment of the fingers, neurovascular status, and local tenderness.

The following findings should be noted:

●Erythema – Erythema may indicate the presence of cellulitis, lymphangitis, or an underlying abscess. The area of erythema should be outlined with an indelible marker (picture 1). This will allow assessment of progression or regression of the infectious process. We find it extremely valuable in patients in the early stages of necrotizing fasciitis who are not systemically ill. The rapid progression of erythema over one to two hours helps differentiate necrotizing fasciitis from cellulitis and indicates the need for surgical intervention. (See 'Necrotizing fasciitis' below.)

●Swelling – The location of any swelling can provide clues about the anatomic location of a deep infection.

●Fluctuance – Fluctuance indicates an underlying abscess (picture 2).

●Lacerations and puncture wounds – Skin lacerations and/or puncture wounds may corroborate the history of trauma, foreign body, or bite wounds.

●Skin ischemia – Discoloration of the skin overlying an abscess indicates ischemia from thrombosis of the subdermal and subcutaneous capillaries and potential impending rupture. Central skin necrosis with surrounding erythema (dermonecrosis) is a feature of methicillin-resistant Staphylococcus aureus infections (picture 3).

●Crepitus – Subcutaneous air manifesting as crepitus can be associated with a gas-forming organism (Clostridium, anaerobic streptococcus, and some coliforms), but it is not always infectious in nature (eg, air gun injuries), but this should be apparent from the patient's history.

●Lymphadenopathy – Epitrochlear and axillary lymphadenopathy often accompany an infection of the forearm.

●Limitation of movement – Limitation of hand, finger, or wrist movement should be documented. Assess for Kanavel cardinal features of pyogenic flexor tenosynovitis: fusiform swelling of the whole digit, partially flexed posture of the digit, tenderness along the flexor tendon sheath, and pain on passive extension of the digit.

Laboratory studies — For patients who are systemically ill or immunocompromised, the white blood cell count may help assess the severity of infection and serve as a useful baseline for comparison to monitor the progress treatment. Other studies (eg, renal function, liver function) should be ordered based upon the patient's underlying medical conditions.

DIAGNOSIS — Most hand infections can be diagnosed on clinical examination based on the presence of pain, erythema, abnormal swelling, drainage, or limitation of movement. (See 'History' above and 'Physical examination' above.)

Imaging — Imaging evaluation may point to the specific diagnosis. The type of imaging depends on the clinical assessment and suspected injuries based on the physical examination and mechanism of injury. Consultation with a radiologist is helpful. If a deep space infection is suspected, ultrasound examination should be performed for confirmation and to look for fluid collections along the tendon sheaths [1]. (See 'Deep hand infections' below.)

Plain radiographs of the affected part should be obtained when clinical findings and history suggest the following conditions. The radiograph also serves as a baseline for future comparison. Radiography may demonstrate:

●Foreign body – A foreign body can serve as a nidus of infection and may require removal for an infection to resolve (image 1). However, radiographs may be misleading if the foreign body is radiolucent.

●Periosteal abnormalities – Periosteal elevation is a nonspecific reaction to tumor, infection, trauma, certain drugs, and some arthritic conditions [2]. Periosteal thickening coupled with bone erosion in the setting of a clinical infection may indicate osteomyelitis. However, imaging findings may be subtle or radiographically absent in the first one to two weeks of infection.

●Gas in the soft tissue – Gas in soft tissue is seen in type I necrotizing fasciitis or gas gangrene caused by clostridia. (See "Clostridial myonecrosis".)

●Joint abnormalities – In the early phase of septic arthritis, radiographs will show widening of the joint space and surrounding soft tissue swelling.

Cultures — Blood and wound cultures determine the infective organism and direct specific antimicrobial treatment.

●Blood cultures should be obtained if septic embolism is suspected (eg, patient with recurrent fever, immunocompromised patient, suspected endocarditis).

●For patients with an open or draining wound, a sample of the drainage should be sent for Gram stain and aerobic and anaerobic culture.

DIFFERENTIAL DIAGNOSIS — Several inflammatory conditions of the hand may be wrongly diagnosed as an acute infection of the hand. Some of the common conditions that mimic acute hand infections include gout, pseudogout, acute calcific tendinitis, retained foreign bodies, extravasation injury, pyoderma gangrenosum, metastatic tumor, and factitious illness. (See "History and examination of the adult with hand pain".)

●Gout – Gout is a disorder of urate metabolism that leads to high levels of uric acid and the formation of urate crystals. Urate crystals can be deposited under the skin, in joints, and within tendon sheaths as "gouty tophi," which cause an intense inflammatory process. Inflamed gouty tophi may be mistaken for a felon, a subcutaneous abscess, pyogenic flexor tenosynovitis, or septic arthritis (picture 4).  

The differentiation between gout and septic arthritis depends on the patient's history, the presence of preexisting gout, and the clinical presentation. If gout is suspected, serum uric acid values and a radiograph should be obtained. It may be difficult to differentiate between gout and infection based only on clinical examination and laboratory and radiological investigations. A trial of colchicine may help differentiate between them. Aspiration of the involved joint and examination of the aspirate under a polarizing light microscope can confirm diagnosis of gout (negatively birefringent needle-shaped intracellular monosodium urate crystals). (See "Clinical manifestations and diagnosis of gout".)

●Pseudogout – Pseudogout (calcium pyrophosphate deposition) is like gout except that it is caused by deposition of calcium pyrophosphate crystals rather than urate crystals. As with gout, differentiation from an infection depends on the patient's history, the presence of preexisting underlying diseases, and the clinical presentation. The aspirate in pseudogout shows positively birefringent rhomboid-shaped calcium pyrophosphate crystals under a polarizing microscope. (See "Clinical manifestations and diagnosis of calcium pyrophosphate crystal deposition (CPPD) disease", section on 'Acute CPP crystal arthritis'.)

●Acute calcific tendinitis – Acute calcific tendinitis is caused by deposition of calcium salts around the tendons and ligaments. Patients present acutely with pain, swelling, erythema, and tenderness overlying tendons or ligaments. However, other signs of infection such as fever, lymphadenopathy, or abnormal laboratory values are absent. Radiographs demonstrate characteristic homogenous calcific densities in the area of tenderness (figure 1). This process is self-limiting, and patients are managed conservatively with analgesics, rest, and splints. (See "Overview of overuse (persistent) tendinopathy".)

●Retained foreign bodies – Retained foreign bodies, especially wooden splinters and thorns, can provoke an inflammatory response that can mimic an infection. Radiographs may be misleading if the foreign body is radiolucent. History is valuable in diagnosis, and removal of the offending foreign body is curative. (See "Infectious complications of puncture wounds".)

●Extravasation injury – The extravasation of vesicant agents at the site of intravenous access, usually over the dorsum of the hand, may present as marked erythema and swelling. This is frequently seen with chemotherapeutic agents and may be mistaken for a secondary infection. (See "Extravasation injury from cytotoxic and other noncytotoxic vesicants in adults".)

●Pyoderma gangrenosum – Pyoderma gangrenosum is an inflammatory skin disease commonly misdiagnosed as an infection. Pyoderma gangrenosum usually begins as small papules that are followed by central necrosis, resulting in a central ulcer with a raised border (picture 5 and picture 6). The diagnosis is often associated with underlying systemic disorders such as inflammatory bowel disease, arthritis, and lymphoproliferative disorders. (See "Pyoderma gangrenosum: Pathogenesis, clinical features, and diagnosis".)

●Metastatic tumor – Metastatic tumors to the hand are rare and usually involve the distal phalanx (picture 7); thus, they can be confused with a pulp space infection or felon. Radiographs are useful in differentiating a tumor from infection. Primary lung tumors are the most common metastatic lesion to the hand. Other tumors that metastasize to the hand include breast, kidney, colon, thyroid, and prostate.

GENERAL MANAGEMENT

Initial care — Initial care of hand infection includes empiric antibiotics, along with pain control and limb elevation to decrease swelling and provide comfort. Specific management of bite wounds, superficial hand infections, and deep space infections are reviewed below. (See 'Bite wounds' below and 'Superficial hand infections' below and 'Deep hand infections' below.)

Antibiotic therapy — Initial antibiotic therapy is empirically based on epidemiologic clues for likely pathogen(s) as well as the Gram stain, if available, while awaiting culture and sensitivity results, which can take two to three days. S. aureus and beta-hemolytic streptococci are the most common pathogenic organisms in the hand [3]. First-generation cephalosporins provide appropriate coverage for methicillin-sensitive S. aureus and streptococcus. Alternative antibiotics are selected in patients with allergies or if the local prevalence of methicillin-resistant S. aureus exceeds 10 to 15 percent [4]. These include erythromycin, clindamycin, doxycycline, trimethoprim-sulfamethoxazole, vancomycin, linezolid, etc [5]. Issues related to coverage for methicillin-resistant S. aureus are discussed separately. (See "Acute cellulitis and erysipelas in adults: Treatment" and "Immediate cephalosporin hypersensitivity: Allergy evaluation, skin testing, and cross-reactivity with other beta-lactam antibiotics" and "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections".)

In addition to the above coverage, empiric anaerobic coverage is also warranted in the setting of bite wounds. (See 'Bite wounds' below.)

Tetanus prophylaxis — For hand injuries, tetanus immunization status should be reviewed, and booster immunization given accordingly. Tetanus toxoid or tetanus immune globulin may be necessary for patients who have received fewer than three doses of tetanus toxoid or if immunization status is uncertain. (See "Tetanus-diphtheria toxoid vaccination in adults", section on 'Immunization for patients with injuries'.)

Splinting — Splint immobilization decreases pain, protects the affected area, and limits opening of tissue planes, thereby restricting the spread of infection. Splinting in a functional position can help protect against flexion contractures, reduce stiffness, and hasten rehabilitation (picture 8). If a single digit is infected, a splint supporting the interphalangeal joints in extension is usually adequate. (See "Basic techniques for splinting of musculoskeletal injuries" and "Overview of finger, hand, and wrist fractures", section on 'Splinting'.)

Elevation — Elevation helps to reduce edema by improving venous and lymphatic drainage. The goal of elevation is to keep the hand above the level of the heart so that dependent drainage can occur. To accomplish appropriate elevation, the patient should be counseled to rest with the extremity above their chest using pillows or commercially available supports while sitting and lying down. The usual arm slings do not provide adequate elevation.

Warm soaks — Application of heat increases the delivery of inflammatory cells to the affected area by local vasodilatation, may enhance antibiotic delivery to the tissue, and improves patient comfort. Moist heat is more effective than dry heat. Warm soaks reach maximum vasodilatory effect in approximately 10 minutes. Short, frequent soaks are preferred over continuous immersion. For cases of more severe infection for which soaks are inadvisable, the affected part can be wrapped in moist, hot towels and then covered with plastic wrap to create a vapor barrier with a dry towel over it for insulation [6,7].

Surgical referral — Some superficial infections of the hand may respond to nonsurgical management, particularly early in their course. Regardless, most hand infections require urgent surgical referral for possible surgical intervention. Prompt evaluation and proper treatment of hand infections can mean the difference between an excellent outcome and permanent disability. Necrotizing infections are true surgical emergencies. The role of surgery in the management of specific etiologies is reviewed below. (See 'Superficial hand infections' below and 'Deep hand infections' below.)

General surgical principles and postoperative care — The aim of surgery is to provide a path for drainage of pus (incision and drainage) and to debride nonviable tissue.

If local anesthesia is being considered, it must be placed some distance proximal to the infection as the local anesthetic agents may not be as effective in the acidic pH of the infection and infection may spread proximally along tissue planes created by infiltration of the local anesthetic. As an example, a wrist block is preferable to a digital block for drainage of subcutaneous abscess over the proximal phalanx.

Typically, surgery needs to be performed at regular intervals (three to five days) until the wound is deemed clear of infection. This is characterized by decreasing pain, swelling, erythema, purulent discharge, and negative tissue cultures [8].

Incisions must allow access, be extensile, and avoid exposing critical structures like tendons, nerves, and vessels as far as possible. Midaxial incisions are better than Bruner/hemi-Bruner incision for the digits, and a curvilinear incision is better than a straight incision for the dorsum of digit/hand [9]. The first debridement is critical because the tissue planes are pristine, it is possible to separate infected tissue from normal tissue and to dissect, identify, and protect the neurovascular structures. The granulation tissue that appears after the initial debridement makes subsequent debridement challenging. As the infection resolves, the swelling becomes better. However, the appearance of granulation and the repeated surgical intervention can lead to adhesions and stiffness. It is important to change dressing regularly (to keep the wound dry), keep the limb elevated (to decrease edema), splinted (to prevent flexion contractures), and mobilize frequently out of the splint (to counteract stiffness).

SPECIFIC ETIOLOGIES

Bite wounds

Animal bites — Dogs are responsible for the majority of animal bites, but cat bites are responsible for the majority of bites that result in infection (76 percent). Dog bites result in larger wounds from the crushing effect of blunt teeth and strong jaws, whereas cat bites result in multiple small puncture wounds (picture 9) that appear innocuous at presentation. However, the cat's sharp teeth can deeply penetrate soft tissues and inoculate bacteria into closed spaces, such as tendon sheaths and joints.

The organism commonly found in animal bite wounds is Pasteurella multocida, which is a gram-negative, nonspore-forming coccobacillus that is found in the normal oral flora of many animals, including dogs and cats. The rabies immunization status of the animal should be documented (if known), and cat owners should be asked whether their cat hunts and eats wild animals. Such cats are at risk of carrying Francisella tularensis, which can cause tularemia. (See "Indications for post-exposure rabies prophylaxis".)

Animal bite wounds can be treated by outpatient observation and oral antibiotics (typically amoxicillin-clavulanate) or by inpatient admission for intravenous antibiotics, and if indicated, surgical irrigation and debridement. However, it is difficult to predict who will need hospitalization. Clinical findings that suggest a more severe, deeper-seated infection include location of the bite over a joint or tendon sheath, erythema, pain, and swelling. These findings merit hospitalization and urgent consultation with a hand surgeon (picture 9) [10]. Animal bites is discussed in more detail elsewhere. (See "Animal bites (dogs, cats, and other mammals): Evaluation and management".)

Human bites — Human bites are serious injuries because of the virulence of the human oral flora [11,12]. The most common human bite injury to the hand is clenched fist injury, also known as a "fight bite." These injuries can be missed in the emergency department because patients may be reluctant to provide an accurate account of the injury and the initial wound may appear innocuous. (See "Human bites: Evaluation and management".)

Fight bite injuries to the hand usually occur with the fist in a clenched position. When the fist makes contact with a victim's mouth, the teeth can easily penetrate the skin and extensor tendon that are stretched tightly over the metacarpal head, thus injuring the underlying bone, cartilage, or joint and resulting in an open metacarpal head fracture, which may progress to septic arthritis (figure 2).

Patients with fight bites present with a lack of normal active extension of the involved joint (extension lag), pain, swelling, and erythema. Purulent drainage from the wound may also be seen. When a patient with a fight bite injury is examined with their digits extended, the small skin laceration may no longer correspond to the site of any fracture, which is frequently overlooked (picture 10). Thus, a radiograph (Brewerton view) should be obtained to look for a fracture of the metacarpal head, retained foreign body (tooth fragment), or osteomyelitis in a delayed presentation. (See "Metacarpal head fractures".)

Human bite injuries often require hospital admission, antibiotics, and operative debridement. Wide exposure of the wound is required, and the joint should be opened and inspected, even if the joint capsule appears intact (picture 11). The tendon can be repaired at the time of washout if the surgeon feels an adequate debridement was achieved, but if this is not the case, the tendon repair and skin closure can be delayed until the infection has been eradicated. After cleansing and debridement, the wound can be left open or loosely approximated. If the clinical symptoms do not improve, radiographs should be repeated and compared with initial radiographs to rule out osteomyelitis. The management of infections from human bites is discussed in detail elsewhere.

Superficial hand infections — Superficial hand infections arise from the skin and subcutaneous tissue in a plane superficial to the tendons [13,14]. These include cellulitis, lymphangitis, paronychia, pulp space infections, herpetic whitlow, subcutaneous abscess, and web space abscess. As a superficial hand infection progresses, it follows the path of least resistance and may involve deeper tissue planes. (See 'Deep hand infections' below.)

Cellulitis — Cellulitis is a diffuse infection of the subcutaneous tissue without pus formation and is characterized by a warm, tender area of erythema and edema that is well demarcated and progresses over time (picture 12). The movements of any underlying joints are painful and restricted.

The patient with cellulitis of the hand requires hospital admission for rest, elevation, warm soaks, antibiotics, and close monitoring. If there is no response to antibiotic therapy (indicated by improvement in patient symptoms and regression of area of erythema), pus formation or a more serious deep hand infection is likely. The diagnosis and treatment of cellulitis is discussed in detail elsewhere. (See "Cellulitis and skin abscess: Epidemiology, microbiology, clinical manifestations, and diagnosis" and "Acute cellulitis and erysipelas in adults: Treatment" and "Soft tissue infections following water exposure".)

Lymphangitis — Lymphangitis of the hand or arm is an infection of the lymphatics. Like cellulitis, it is not pus forming. However, unlike cellulitis, it has a distal nidus with erythematous streaks that spread proximally up the arm (picture 13). There may be associated palpable tender epitrochlear or axillary lymphadenopathy.

A patient with lymphangitis requires hospital admission for rest, elevation, warm soaks, antibiotics, and close monitoring. If there is no response to antibiotic therapy, a more serious deep hand infection is likely. The diagnosis and treatment of lymphangitis is discussed in detail elsewhere. (See "Lymphangitis" and "Soft tissue infections following water exposure".)

Surgical site infection — Infections after elective surgeries of the hand are uncommon (1 to 1.5 percent). Most of these are superficial surgical site infections; deep surgical site infections are rare (0.1 to 0.3 percent) [15]. The most common organism involved is S. aureus, with some infections caused by streptococci or mixed flora. Patients with diabetes or immunocompromised patients are more likely to develop infections with gram-negative organisms. Preoperative surgeon hand washing for at least 90 seconds and administration of preoperative prophylactic antibiotics at least five minutes before surgery can help reduce the risk of postoperative infection. Antibiotic prophylaxis is only indicated for operations lasting more than two hours, contaminated or dirty wounds, or open fractures [16]. (See "Overview of the evaluation and management of surgical site infection" and 'Deep fascial space infections' below.)

Paronychia — Acute paronychia is a bacterial infection of the lateral nail fold characterized by erythema, swelling, and tenderness along the nail fold, especially in the dorsolateral corner (picture 14) [17,18]. Chronic paronychia is an inflammatory dermatosis of the nail fold due to chronic exposure to irritants and allergens (picture 15). The diagnosis and treatment of acute and chronic paronychia is discussed elsewhere. (See "Paronychia".)

If left untreated, acute paronychia can form an abscess within the nail fold. It usually begins in the lateral nail fold (paronychium), gradually progressing to involve the proximal nail fold (eponychium) and then the opposite lateral nail fold (runaround abscess). The nail plate may be lifted up, and, in some cases, the infection can extend to the pulp space (picture 16)

For patients who present early without an abscess, nonsurgical treatment of acute paronychia and acute eponychia is appropriate and consists of oral antibiotics, warm soaks, rest, and elevation.

Surgical drainage (figure 3A-B) is indicated in patients who develop an abscess.

Pulp space infections — The digital pulp, the fleshy mass at the digital tips, is divided into multiple compartments by fibrous septae that provide structural support (figure 4)[13,14]. A severe infection or abscess of the pulp space, called a felon, results in increased pressure and can lead to ischemic necrosis of surrounding tissue, osteomyelitis, flexor tenosynovitis, or septic arthritis of the distal interphalangeal joint (DIPJ). A pulp abscess usually occurs after a puncture wound but may also result from untreated acute paronychia. (See 'Paronychia' above.)

Pulp abscesses account for 15 to 20 percent of all hand infections. The thumb and index finger are the most commonly affected digits [7]. Patients with pulp space infections present with pain, cellulitis, and an associated tender fluctuant swelling. The pain is severe and throbbing, is worse in the dependent position, and usually does not allow the patient to sleep. The swelling is limited to the soft tissue around the distal phalanx, and an area of imminent rupture (pointing) may be obvious (figure 5). Occasionally, the abscess may spontaneously discharge through the skin, decompressing it and thus reducing symptoms. If this has happened, a radiograph should be obtained to look for any retained foreign bodies and rule out involvement of the distal phalanx.

A very early presentation of a pulp space infection without a fluctuant swelling may be treated with warm soaks, rest, elevation, and oral antibiotics. However, most patients with a pulp abscess require surgical intervention. A simple incision and drainage procedure may provide temporary relief; however, in our experience, debridement of the abscess cavity is best accomplished in the operating room because the infection may be more extensive than the symptoms and clinical appearance suggest.

Herpetic whitlow — Herpetic whitlow is a viral infection of the hand caused by herpes simplex virus (HSV-1 and HSV-2) [19,20]. Herpetic whitlow has a bimodal age distribution affecting children less than 10 years of age and young adults between 20 and 30 years of age. Herpetic whitlow is caused by HSV-1 in children, and in adults, it can be caused by either HSV-1 or HSV-2. HSV spreads by direct digital contact with secretions, from lesions of infected patients, or from secretions of asymptomatic carriers.

The lesion in herpetic whitlow can be a single vesicle or a cluster of vesicles. The lesions are initially clear but become turbid, yellow, and appear purulent with an erythematous base (picture 17 and picture 18 and picture 19). These lesions appear after an incubation period of 2 to 20 days following inoculation and can coalesce to form larger blisters. The lesions may spread around the paronychial folds, and satellite lesions may appear. The lesions are associated with tingling and burning pain of the hand that is disproportionate to the clinical findings. Occasionally patients have flu-like symptoms, including fever and epitrochlear/axillary lymphadenitis. When the blister (or vesicle) is unroofed, non-purulent fluid is released, and the underlying tissue has a honeycomb appearance that is diagnostic for herpetic whitlow.

The diagnosis of herpetic whitlow is clinical. Diagnostic tests include viral culture, serum antibody titers, Tzanck smear, and lesion-specific antigen detection [19]. Viral culture is most sensitive but requires one to four days for a positive result. Serum antibody titers take about three weeks. Thus, both these tests are not useful for rapid confirmation. A Tzanck smear or antigen detection in samples of vesicle fluid or scrapings can be used for early diagnosis. However, the Tzanck smear is not specific for HSV, but it is relatively inexpensive. (See "Office-based dermatologic diagnostic procedures", section on 'Tzanck smear'.)

Herpetic whitlow is often confused with acute paronychia or a pulp abscess (see 'Pulp space infections' above). However, unlike a bacterial infection, the pulp space is not tense. Herpetic whitlow usually affects only one digit; if multiple digits are affected, other vesicle-forming viral infections like the Coxsackievirus infection (enterovirus) should be suspected. (See "Hand, foot, and mouth disease and herpangina".)

The treatment of primary herpetic whitlow is conservative (rest, elevation, and anti-inflammatory agents). Surgery is contraindicated because it will only spread the infection and may result in secondary bacterial infection. Unless a secondary bacterial infection is suspected, herpetic whitlow does not require use of antibiotics. A dry dressing is used to cover the digit to prevent transmission of the infection. The natural history of untreated uncomplicated herpetic whitlow is complete resolution within three weeks. The vesicles evolve into shallow ulcers that form crusts that eventually peel off to leave healed epidermis below. The satellite lesions, shallow ulcers, and crusts last for about 12 days and coincide with the period of viral shedding, during which time the patients are most infectious.

While topical 5% acyclovir shortens the duration of labial and genital HSV lesions, it has not been studied in herpetic whitlow. Immunocompetent patients with primary herpetic whitlow may benefit from topical acyclovir therapy. Patients with primary HSV infection at multiple sites or recurrent herpetic whitlow may be considered for oral antiviral therapy [20]. A total daily dose of 1600 to 2000 mg given at the onset of prodromal symptoms has been shown to prevent viral shedding and shorten the duration of symptoms. Similarly, 200 mg of acyclovir taken orally three to four times daily has been shown to prevent or decrease recurrence rates. However, the dose and duration of treatment have not been optimized [19]. Intravenous acyclovir is recommended only for immunocompromised patients or those with disseminated HSV infections. (See "Treatment and prevention of herpes simplex virus type 1 in immunocompetent adolescents and adults", section on 'Cutaneous disease'.)

After an infection, HSV passes into a latent phase residing in the sensory ganglion. About 20 to 50 percent of affected patients experience recurrence that may be triggered by illness, fever, sun exposure, menstruation, or other physiologic or psychologic stressors. Recurrent infections are typically milder and shorter in duration [19]. Complications from herpetic whitlow are rare and include nail dystrophy, hyperesthesia, and systemic viremia.

Subcutaneous abscess — A subcutaneous abscess of the digits or hand is usually the result of minor penetrating trauma that was missed or not treated.

A subcutaneous abscess of the digit presents with localized swelling, erythema, and restricted motion at the adjacent joints (picture 20). The digit is usually in a flexed posture, and there may be evidence of an inflamed puncture wound from a penetrating injury. In late presentations, the abscess may be pointing or discharging through a sinus.

Subcutaneous abscesses of the hand can occur on the palmar or the dorsal aspect of the hand.

●Palmar abscess – A subcutaneous abscess of the palm presents with erythema and mild swelling on both the palmar and dorsal aspect of the hand. Abscesses of the palmar skin are typically localized because the fibrous septae anchoring palmar skin limit the spread of infection (picture 21). Palpation of the tendon sheath proximal and distal to a palmar subcutaneous abscess will help differentiate it from pyogenic flexor tenosynovitis that is confined along the path of the tendon sheath.

●Dorsal abscess – A subcutaneous abscess of the dorsum of the hand is associated with significant dorsal hand swelling, a tender fluctuant mass, and pain with extension of the digits. The dorsal skin of the hand is loosely anchored to the underlying tissue, which allows the spread of infection into two potential spaces: the dorsal subcutaneous space, which is superficial to the extensor tendons, and the dorsal subaponeurotic space, which is deep to the extensor tendons (figure 6).

A radiograph should be obtained to look for any foreign bodies and rule out involvement of the bone or joints.

Drainage to decompress the abscess will reduce pain in the period before surgical debridement can be performed. Patients who require extensive debridement for dorsal abscesses may need additional surgical procedures to cover the resulting soft tissue defect (picture 22). (See "Skin autografting".)

Web space abscess — An interdigital web space infection is a subcutaneous abscess involving the web space where the infection may be present on the palmar and dorsal aspect simultaneously (picture 23). It is also known as a collar button abscess because of its anatomic resemblance to buttons used on dress shirts in the early nineteenth century. Advanced web space abscesses of the collar button types are rarely seen in modern times unless the infection is not treated.

A web space abscess usually results from a penetrating injury or a fissure in the web space. It may also result from infection of a palmar callus in manual laborers or spread from an adjacent palmar subcutaneous abscess. The infection begins in the palmar subcutaneous portion of the web space and then spreads dorsally over the superficial transverse metacarpal ligament to involve the dorsal subcutaneous space (figure 7).

A patient with a web space abscess presents with pain and swelling limited to the web space and distal palm. There may be greater swelling on the dorsal aspect of the web, although the primary focus of infection is on the palmar side. The adjacent digits are usually in an abducted position, and this may help differentiate it from a pure dorsal or palmar subcutaneous abscess, where the digits are in the normal adducted position.

A web space abscess requires a combined palmar and dorsal surgical approach for adequate drainage and debridement (figure 8).

Deep hand infections — Deep hand infections involve the tendons and structures deep to the tendon sheaths. These include synovial space infections, deep fascial space infections, septic arthritis, and necrotizing fasciitis. In the early stage, the infection is limited by the compartmentalized anatomy of the hand, and, if left untreated, they may rupture superficially, spread to the adjoining compartments, or involve the underlying bone and joints [13,14].

Although uncommon, both typical and atypical mycobacterial infections should be considered in the differential diagnosis of hand infections that are refractory to treatment. Mycobacterial infections are typically associated with the tendon sheath and synovial tissues lining the tendon. A tissue biopsy should be obtained if the diagnosis is suspected because mycobacteria are difficult to culture. (See "Cutaneous manifestations of tuberculosis" and "Soft tissue infections following water exposure".)

Synovial space infections — The flexor tendons of the hand are enclosed in a double-layered synovial sheath composed of an inner visceral layer and an outer parietal layer, which create a closed system (figure 9). The tendon sheath of the flexor pollicis longus continues proximally as radial bursa while the tendon sheaths of the fingers (usually the ulnar digits) continue proximally as the ulnar bursa. The radial and ulnar bursa end proximal to the wrist. They can communicate with each other via the space of Parona (figure 10), which is a potential space deep to the tendons of the flexor digitorum profundus (sublimis) and superficial to the pronator quadratus.

The synovial spaces intercommunicate and provide an optimal environment for bacterial growth because they are poorly vascularized and rich in synovial fluid [13,21,22]. Bacterial proliferation within the synovial sheath rapidly destroys the tendon's gliding mechanism and leads to increased pressure within the sheath, which obstructs the blood flow and can cause tendon necrosis and rupture. The infection can spread from the bursa into the surrounding soft tissue compartments. The infection can also track from the radial to the ulnar bursa and vice versa to form a so-called "horseshoe abscess."

Pyogenic flexor tenosynovitis — Patients with an isolated infection of the digital flexor sheaths (pyogenic flexor tenosynovitis) typically present with fusiform swelling of the whole digit, partially flexed posture of the digit, tenderness along the flexor tendon sheath, and pain on passive extension of the digit (Kanavel's cardinal features of pyogenic flexor tenosynovitis), although all features may not be seen in an early presentation (picture 24) [21].

Patients with an infection of the radial bursa, ulnar bursa, space of Parona, or a combination of these (horseshoe abscess) present with a flexed attitude of the wrist; swelling; and tenderness along the thenar, hypothenar, and/or the distal wrist crease because of the associated thumb and/or small finger flexor tenosynovitis.

In general, the management of tenosynovitis requires antibiotic therapy and surgical intervention (picture 25). (See "Infectious tenosynovitis".)

Deep fascial space infections — Deep fascial space infections are surgical emergencies; there is no role for nonoperative treatment.

The palm has three potential closed spaces with well-defined anatomic borders: the thenar, the midpalmar, and the hypothenar space (figure 10) [23]. These spaces are deep to the flexor tendons but superficial to the interosseous muscles. Infections in these spaces most commonly occur following a penetrating injury but occasionally can result from extension from a subcutaneous abscess, adjacent pyogenic flexor tenosynovitis, or hematogenous spread from a distant site.

All deep palmar space infections present with palmar swelling and tenderness over the involved palmar space and generalized dorsal swelling:

●A thenar space abscess is characterized by a widely abducted thumb and fullness on the dorsum of the first web space, with pain on adduction or opposition of the thumb (picture 26).

●A midpalmar space abscess is characterized by loss of the normal palmar concavity (picture 27). The long and ring fingers assume a partially flexed posture, and there is pain on passive extension of these fingers.

●Hypothenar space infections have much less palmar and dorsal swelling than thenar or midpalmar space infections. In addition, there is no involvement of the fingers or the flexor tendons.

An ultrasound examination can help confirm the presence and location of an abscess cavity and thus differentiate deep fascial space infection from other entities in the differential diagnosis such as pyogenic flexor tenosynovitis, radial or ulnar bursal infections, and subcutaneous abscess. Radiographs are useful to evaluate for a retained foreign body.

The incisions used to approach to thenar space, midpalmar space, and hypothenar space infections are illustrated in the figures (figure 11 and figure 12 and figure 13). For deep fascial space infection, the surgical approach identifies the limits of the infection to adequately debride to normal appearing tissue proximally and distally. Typically for any infection extending into the palm, it is safer to perform a carpal tunnel release. The superficial palmar arch limits proximal clearance of palmar infections and proximal debridement would not be possible without doing a carpal tunnel release.

Septic arthritis — Septic arthritis usually refers to bacterial infection in a joint but also includes fungal and mycobacterial infections that involve the joint [24]. Magnetic resonance imaging is useful in identifying areas of bone involvement, joint effusion, or soft tissue abscess.

Patients with septic arthritis present with a red, swollen, warm, and tender joint that is painful on passive motion. The differential diagnosis of bacterial arthritis includes gout, pseudogout, arthritis, and Lyme disease, each of which can present with acute involvement of one or a few joints (table 1).

Treatment of acute bacterial arthritis requires appropriate antimicrobial agents and adequate joint drainage. All septic joints must be explored early to avoid cartilage damage from the disease process (picture 28). (See "Septic arthritis in adults".)

Necrotizing fasciitis — Necrotizing fasciitis is a rapidly progressing, life-threatening soft tissue infection characterized by widespread fascial necrosis and relative sparing of underlying muscle caused by a toxin-producing bacterium [25,26]. (See "Necrotizing soft tissue infections", section on 'Necrotizing fasciitis'.)

Patients with necrotizing fasciitis feel much worse than suggested by their clinical appearance and may demonstrate systemic signs of sepsis including fever, dehydration, hypotension, and electrolyte imbalance. It is important to differentiate necrotizing fasciitis from cellulitis because the early presentation of both these conditions is similar. (See 'Cellulitis' above.)

Necrotizing fasciitis requires emergent surgical intervention. Initial treatment involves resuscitation and stabilization of the patient and empiric broad-spectrum antimicrobial therapy. (See "Necrotizing soft tissue infections", section on 'Antibiotic therapy'.)

Thereafter, the initial debridement should be performed as soon as possible. Surgical treatment consists of wide debridement of skin, subcutaneous tissue, fascia, and any necrotic muscle. The initial debridement is the most important and determines the outcome of treatment (picture 29). The diagnosis and treatment of necrotizing fasciitis is discussed in detail elsewhere. (See "Surgical management of necrotizing soft tissue infections", section on 'Surgery'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Human bites" and "Society guideline links: Rabies" and "Society guideline links: Skin and soft tissue infections".)

SUMMARY AND RECOMMENDATIONS

●Evaluation – Prompt evaluation and proper treatment of hand infections can mean the difference between an excellent outcome and permanent disability. Initial evaluation includes a focused history and examination, laboratory evaluation, and imaging. The area of erythema should be marked to help document progression of the infection. With bite wounds, rabies immunization status should be documented. (See 'Anatomy and classification' above and 'Bite wounds' above.)

•Superficial infections – Superficial hand infections arise from the skin and subcutaneous tissue in a plane superficial to the tendons. These include cellulitis, lymphangitis, paronychia, pulp space infections, herpetic whitlow, subcutaneous abscess, and web space abscess. As a superficial hand infection progresses, it follows the path of least resistance and may involve deeper tissue planes. (See 'Superficial hand infections' above.)

•Deep infections – Deep hand infections are deep to the tendon sheaths and include synovial space infections, deep fascial space infections, septic arthritis, and necrotizing fasciitis. Although less common overall, both typical and atypical mycobacterial infections should be suspected with hand infections that are refractory to treatment (typically deep infection). Because mycobacteria are difficult to culture, a tissue biopsy is often necessary. (See 'Deep hand infections' above.)

●Differential diagnosis – Acute hand infections may be mistaken for several inflammatory or other conditions of the hand. Some of these include gout, pseudogout, acute calcific tendinitis, retained foreign bodies, extravasation injury, pyoderma gangrenosum, and metastatic tumor. (See 'Differential diagnosis' above.)

●Management – Early and superficial infections of the hand may respond to nonsurgical management. Empiric antibiotics should be initiated, and hand elevation and heat will provide comfort for the patient. Most acute infections of the hand require early surgical intervention. (See 'General management' above.)