Systemic juvenile idiopathic arthritis: Clinical manifestations and diagnosis

INTRODUCTION — Systemic juvenile idiopathic arthritis (sJIA, formerly called Still's disease or systemic juvenile rheumatoid arthritis) is officially classified as a category of JIA that includes patients characterized by daily fever in a quotidian pattern, rash, and arthritis. It is termed "adult-onset Still's disease" (AOSD) when it begins in patients over the age of 16 years. sJIA accounts for approximately 10 to 20 percent of all cases of JIA. It typically affects males and females equally and may present in children as young as one year of age or younger. (See "Juvenile idiopathic arthritis: Epidemiology and immunopathogenesis".)

The clinical manifestations of sJIA that distinguish it from other categories of JIA are reviewed here (table 1), as is the diagnosis of sJIA. The management, complications, and prognosis of sJIA, as well as other categories of JIA such as oligoarticular, polyarticular, enthesitis related, and psoriatic JIA, and general topics on JIA are discussed separately. (See "Systemic juvenile idiopathic arthritis: Treatment" and "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications" and "Oligoarticular juvenile idiopathic arthritis" and "Polyarticular juvenile idiopathic arthritis: Clinical manifestations, diagnosis, and complications" and "Spondyloarthritis in children" and "Psoriatic juvenile idiopathic arthritis: Pathogenesis, clinical manifestations, and diagnosis" and "Psoriatic juvenile idiopathic arthritis: Management and prognosis" and "Classification of juvenile idiopathic arthritis" and "Juvenile idiopathic arthritis: Epidemiology and immunopathogenesis".)

OVERVIEW — Patients with sJIA fall into the category of systemic arthritis in the 2004 International League of Associations for Rheumatology (ILAR) proposed classification of the childhood arthritides [1]. Children with this illness comprise between 10 and 20 percent of all cases of JIA. However, data suggest that this illness is a unique condition similar to the autoinflammatory family of diseases, with distinct manifestations and treatment response patterns that distinguish it from the other diseases categorized as JIA [2,3]. (See "Classification of juvenile idiopathic arthritis" and "The autoinflammatory diseases: An overview".)

This form of JIA is very distinctive but may be difficult to diagnose for the following reasons:

●Arthritis, although necessary to establish a definitive diagnosis, may not be evident early in the course of the disease [1,4].

●The systemic disease features, such as fever and rash, may not be present in their typical forms initially, even though these features are also necessary to establish a definitive diagnosis [1,4].

●There are currently no specific diagnostic tests for this disorder.

●Affected children are often quite ill with high, spiking fevers; rashes; markedly elevated white blood cell (WBC) counts; anemia; highly elevated acute phase reactants; and often lymphadenopathy, hepatosplenomegaly, or pericarditis. Most such children are initially thought to have an infection or a malignancy, and the correct diagnosis is only suspected after there has been no response to antibiotic therapy and infectious causes and malignancy have been excluded.

Some children who present with fever, rash, and diffuse joint pain may in fact have an infection, leukemia, or other serious condition that requires different treatment. Thus, it is essential that clinicians thoroughly exclude other conditions before making this diagnosis since there is no diagnostic test for sJIA.

CLINICAL MANIFESTATIONS

Age at onset — Peak incidence is between one and five years of age, but sJIA can occur at any age (onset after 16 years of age is called adult-onset Still's disease [AOSD]) [5]. There can be delays in diagnosis, especially if the symptoms are not typical, which is often the case early on.

Presenting features — Children with sJIA may present with a variety of articular and extraarticular signs and symptoms. In one large case series from several tertiary centers in Pennsylvania, 136 patients were diagnosed with sJIA from 1990 to 2005 [4]. The following manifestations at disease onset and relative frequency were noted:

●Fever – 98 percent

●Arthritis – 88 percent (8 percent with monoarthritis, 45 percent with oligoarthritis, and 47 percent with polyarthritis)

●Rash – 81 percent

●Lymphadenopathy – 31 percent

Articular manifestations — Arthralgias are common early in the course of sJIA, but arthritis is not always prominent. In addition, there may be a prolonged interval between the onset of systemic symptoms and the appearance of arthritis. Any number of joints may be involved when arthritis becomes apparent. Disease in the wrists, knees, and ankles is most typical, but the hands, hips, cervical spine, and temporomandibular joints are also sometimes affected. Unlike the oligoarticular and polyarticular subtypes of JIA, the arthritis of sJIA may begin in the hips and may progress very rapidly, causing severe damage and dysfunction and need for early joint replacement surgery, as well as loss of growth potential in younger patients. Tenosynovitis and synovial cysts that may be quite large are seen in some patients. (See "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications", section on 'Growth retardation'.)

Micrognathia and cervical spine fusion due to arthritis in the temporomandibular joints and neck were often present in children with longstanding sJIA. In the past, these abnormalities affected as many as 50 percent of children with disease onset in the first decade of life. Earlier and more targeted treatment has led to a marked decrease in these complications. (See "Systemic juvenile idiopathic arthritis: Treatment".)

Extraarticular manifestations — The most common extraarticular manifestations are quotidian fever and a macular, salmon-pink rash.

Fever — Children with sJIA usually come to medical attention urgently because they typically present with high fevers. The key finding that suggests the diagnosis is the daily but intermittent nature of the fever. The diagnosis is strongly in doubt if the patient's temperature does not spontaneously return to normal on a daily basis. This pattern of one high spike of fever a day to ≥38.5°C (≥101.3°F) with normal or subnormal temperatures during the rest of the 24-hour period is called "quotidian fever" (figure 1). Some children have a pattern with more than one spike of fever a day, but their temperature also usually returns to normal in between the fever spikes. Low-grade fevers are not typical for sJIA. Affected children are characteristically ill appearing when febrile but seem to improve dramatically when their temperature is normal. If rash is present (see 'Rash' below), it also tends to appear or worsen when the fever is present. These features, in addition to the lack of response to antibiotics, help to distinguish patients with sJIA from those with an infection. (See 'Differential diagnosis' below.)

Some children do not have this typical fever pattern initially and have continuous fevers, fever that does not occur daily, or no fever at all. If untreated, however, most patients will eventually develop this highly specific fever pattern.

Rash — An evanescent, macular, salmon-pink rash is frequently present (picture 1). It usually consists of multiple round to oval macules that are slightly raised and are of differing sizes. The smaller ones have a slight pallor surrounding them, and the larger ones commonly exhibit central pallor. The rash may not be noticed, because it is often only in scattered locations, is fleeting, and may not be very prominent. Additionally, the rash may be difficult to see in darker-skinned individuals. Thus, careful inspection of the skin is important when sJIA is suspected. The rash is brought out by heat and touch and is often found in the axillae and around the waist but may be present anywhere on the body. It is most prominent when the child is febrile. Unlike viral exanthems, which persist, the rash often fades as the temperature returns to normal, only to reappear with the next fever spike. The rash also may appear following stroking of the skin or other minor trauma (Koebner phenomenon) (picture 2). The rash can be intensely pruritic in some patients. It can become somewhat confluent and become urticarial in appearance, especially in those patients who scratch themselves because of the pruritus [6]. Some children with sJIA can also have atypical skin rashes including urticarial, dyschromic, and crusted lesions, and their presence is associated with high systemic inflammation and macrophage activation syndrome (MAS) [7].

Macrophage activation syndrome — MAS is a severe complication of sJIA that can occur within the first few days to weeks of sJIA disease onset and should be treated as a life-threatening emergency. It is considered one of the secondary forms of hemophagocytic lymphohistiocytosis. It is characterized by persistent fever, atypical rash (if present), coagulopathy, decreasing white and red blood cell counts and platelet counts, and hepatitis as well as extreme hyperferritinemia, among other features. A collaborative effort of several international rheumatology organizations has developed laboratory classification criteria for a more prompt diagnosis of sJIA-associated MAS [8]. MAS is discussed in greater detail separately. (See "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications", section on 'Macrophage activation syndrome'.)

Other clinical findings — In addition, the following clinical features can be observed:

●Hepatomegaly, splenomegaly, and lymphadenopathy are commonly found and can be prominent. This combination frequently raises suspicion of a malignancy. In sJIA, lymph node biopsy shows benign reactive hyperplasia. (See 'Malignancy' below.)

●Pericarditis and other forms of serositis are a feature of sJIA. Typically, a small pericardial effusion that is not usually clinically significant is often noted on echocardiogram. However, the pericarditis can cause significant symptoms in some patients. Large pericardial effusions are rare but, when present, may result in tamponade, in some cases with a fatal outcome.

●Pulmonary manifestations include pleural effusion, which most often present during the acute phase of the illness in patients with serositis. Interstitial lung disease, alveolar proteinosis, and pulmonary hypertension are rare but serious findings that are increasingly reported [9]. The following clinical features are often seen with sJIA-associated lung disease: acute onset of clubbing and/or erythema of fingertips, respiratory symptoms such as shortness of breath and dyspnea, atypical abdominal pain, and recurrent episodes of MAS, as well as severe infusion reactions, especially to tocilizumab. Patients who develop sJIA-associated lung disease appear to have a poor prognosis, with limited data indicating a mortality rate as high as 40 to 60 percent [10,11].

●Pharyngitis, a common feature of AOSD, is not commonly seen in children but is occasionally a prominent complaint in older children and teenagers.

●Some children may initially present with features suggestive of Kawasaki disease (KD) or atypical KD, including coronary artery dilatation on echocardiogram in some cases [12,13]. These patients are often only diagnosed with sJIA when they fail to respond to treatment for KD. (See "Kawasaki disease: Clinical features and diagnosis" and "Incomplete (atypical) Kawasaki disease", section on 'Clinical presentation of typical versus incomplete KD'.)

LABORATORY FINDINGS — Characteristic patterns of laboratory abnormalities are frequently present and suggestive of the disease, although there are no tests that are specific for the diagnosis:

●White blood cell (WBC) counts are almost always elevated, and counts in the 20,000 to 30,000/mm³ range are not uncommon. At times, they may be alarmingly high, exceeding 60,000 to 80,000. Granulocytes always predominate [4].

●There is usually a marked reactive thrombocytosis, with the platelet count typically in the 500,000 to 800,000/mm³ range, although it may exceed 1,000,000/mm³ [4]. Thrombocytopenia or even low normal platelet counts (eg, less than 200,000/mm³) should prompt careful evaluation for an alternative diagnosis (eg, bone marrow aspiration to exclude leukemia). A sudden, rapid drop in the platelet count, especially when accompanied by a sudden decrease in red and white blood cell counts, may herald the development of macrophage activation syndrome (MAS), a form of hemophagocytic lymphohistiocytosis [14]. (See 'Malignancy' below and "Clinical features and diagnosis of hemophagocytic lymphohistiocytosis", section on 'Rheumatologic disorders/MAS' and "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications", section on 'Macrophage activation syndrome'.)

●The erythrocyte sedimentation rate (ESR) is typically highly elevated in children with active sJIA and may exceed 100 mm/hour. A normal ESR is rare when the disease is active. The level of C-reactive protein (CRP), another acute-phase reactant, is usually elevated as well. The combination of a sudden fall in the ESR and in the platelet count to "normal" levels may also herald the onset of MAS in an unwell child rather than clinical improvement. Careful evaluation of children with this combination of findings is essential. A dramatic rise in the serum ferritin level or in D-dimer levels also strongly suggests the onset of MAS. A ferritin/ESR ratio of >80 has been proposed as a biomarker of MAS [15]. (See "Clinical features and diagnosis of hemophagocytic lymphohistiocytosis", section on 'Rheumatologic disorders/MAS' and "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications", section on 'Macrophage activation syndrome'.)

●Hyperferritinemia (often greater than 1000 but can be even ≥50,000 ng/mL) is also common in children with active sJIA, even if overt MAS is not present, although ferritin is normal in a minority of cases. It can be useful in raising suspicion for the diagnosis of sJIA since very few other illnesses are associated with such extreme elevations in ferritin levels [3]. (See "Clinical features and diagnosis of hemophagocytic lymphohistiocytosis", section on 'Rheumatologic disorders/MAS'.)

●Children with active sJIA also show markedly elevated serum markers of innate immune activation. This includes the alarmin proteins S100A8/A9 (calprotectin or MRP8/14) and S100A12 (calgranulin C), which are highly elevated in sJIA compared with other subtypes of JIA as well as infections [16,17]. In addition, patients with sJIA also have high serum concentrations of the cytokine interleukin (IL) 18, with the highest levels associated with risk for MAS [18,19]. Although these biomarkers are not widely clinically available, they are helpful in the differential diagnosis of sJIA.

●Minor elevations in aspartate aminotransferase (AST) and alanine aminotransferase (ALT), hypoalbuminemia, increased globulin levels, and low-grade D-dimer positivity are often present. However, markedly elevated hepatic enzyme abnormalities, prolonged clotting times, or an increase in D-dimers should prompt immediate consideration of MAS. (See "Systemic juvenile idiopathic arthritis: Course, prognosis, and complications", section on 'Macrophage activation syndrome'.)

●Anemia is commonly present but rarely profound. It is primarily due to decreased synthesis and poor absorption of oral iron rather than increased destruction. The anemia can be exacerbated by chronic gastrointestinal blood loss induced by nonsteroidal antiinflammatory drugs (NSAIDs). Thus, children with sJIA can become iron deficient over time if the systemic disease does not respond to treatment and sometimes need parenteral iron therapy. (See "Iron deficiency in infants and children <12 years: Treatment".)

●The urinalysis is typically normal in children with sJIA. Some children manifest low-grade proteinuria when febrile, but significant proteinuria or hematuria are almost never seen in patients with sJIA. Secondary amyloidosis resulting in proteinuria that can reach the nephrotic range has been reported in the past in the European literature but is exceedingly rare [14]. Thus, the presence of hematuria or significant proteinuria in combination with fever, arthritis, and rash should prompt consideration of another diagnosis, such as systemic lupus erythematosus or a systemic vasculitis rather than JIA. (See "Childhood-onset systemic lupus erythematosus (SLE): Clinical manifestations and diagnosis" and "Vasculitis in children: Incidence and classification" and "Vasculitis in children: Evaluation overview" and "Vasculitis in children: Management overview".)

●Antinuclear antibodies (ANA) and rheumatoid factor (RF) in high titer are almost always negative in sJIA. Their presence should prompt consideration of alternative diagnoses. A positive RF, for example, may be associated with RF-positive polyarticular JIA, Sjögren's disease, or the early onset of adult-type rheumatoid arthritis (RA) in teenagers (although these disorders are not associated with high fevers and other sJIA features). Both RF and ANA may be present in children with mixed connective tissue disease (MCTD). However, these conditions rarely mimic sJIA. False-positive results may be seen in some patients. Some chronic infectious processes, such as subacute bacterial endocarditis, can cause unexplained fevers and a positive RF. (See "Polyarticular juvenile idiopathic arthritis: Clinical manifestations, diagnosis, and complications" and "Diagnosis and classification of Sjögren’s disease" and "Clinical manifestations of rheumatoid arthritis".)

REFERRAL — There may be a prolonged delay between the onset of fever and the development of arthritis [4], but, according to the International League of Associations for Rheumatology (ILAR) criteria, a definitive diagnosis of sJIA cannot be made until arthritis is present and is shown to be persistent. However, these patients are often very ill and need urgent evaluation and treatment. Thus, any patient suspected of having sJIA should be referred as quickly as possible to a pediatric rheumatologist, if available, for their expert opinion and management. A pediatric rheumatologist may be able to make a diagnosis of probable sJIA and begin appropriate therapy before the required six weeks of symptoms and arthritis have elapsed, as long as other conditions have been excluded.

DIAGNOSIS — sJIA is a diagnosis of exclusion. The hallmark of sJIA is the combination of intermittent but daily fevers greater than 38.5ºC (quotidian fever pattern) and arthritis [1]. To fulfil criteria from the International League of Associations for Rheumatology (ILAR), fever must be present for at least two weeks and arthritis for at least six weeks in order to make a definitive diagnosis [1]. This disease duration is critical since many viral and other postinfectious forms of arthritis are associated with fever, as are malignancies. However, these diseases often lack the characteristic intermittent spiking fever pattern of sJIA and, in the case of viral or postinfectious arthritis, will self-resolve. (See "Viral arthritis: Causes and approach to evaluation and management".)

As understanding of the immunopathogenesis of sJIA increases, the requirement of arthritis for diagnosis is under debate. A modified set of criteria has been developed and published by the Childhood Arthritis and Rheumatology Research Alliance (CARRA) sJIA workgroup in order to facilitate earlier diagnosis and treatment, and a set of criteria for sJIA have been proposed that does not include arthritis as a required criterion [20]. However, consultation with a pediatric rheumatologist who has the appropriate expertise in the diagnosis and treatment of this disease should be sought prior to treatment initiation [21]. (See "Systemic juvenile idiopathic arthritis: Treatment".)

A thorough work-up for fever of unknown origin is recommended prior to treatment to exclude infection, inflammatory bowel disease (IBD), and malignancy, such as blood and urine cultures, viral studies, and radiographs of the chest and affected bones and joints. Obtaining computed tomography (CT) of the abdomen and pelvis, as well as a bone marrow aspiration, prior to treatment is advised, especially if a pediatric rheumatologist is unavailable to confirm the diagnosis.

By definition, sJIA cannot be diagnosed if onset of symptoms occur after the age of 16 years. However, there is a similar and probably identical illness that occurs in adults and adolescents above the age of 16 years called adult-onset Still's disease (AOSD) [22]. Recurrent disease after the age of 16 years should not be called AOSD, since it is simply a continuation of sJIA. (See "Clinical manifestations and diagnosis of adult-onset Still's disease".)

DIFFERENTIAL DIAGNOSIS — sJIA can be confused with a number of other disorders, including viral or postinfectious arthritis, other rheumatic or autoinflammatory diseases, malignancy, or malaria.

Bacterial bone and joint infections — Septic arthritis and osteomyelitis often present with high-grade fever, joint pain, and swelling, as well as limping. The white blood cell (WBC) count and acute-phase reactants are also often highly elevated. There is almost always localization to one joint or limb in these disorders, although this can occur in sJIA as well. Children with bone or joint infections appear acutely unwell. In addition, in contrast to the joint involvement in JIA, these children often have severe pain in the joint, which is usually hot and red with little mobility whatsoever in the case of septic arthritis, and exquisite bone point tenderness similar in severity to that seen in malignancies in the case of osteomyelitis (see 'Malignancy' below). Furthermore, these patients typically have a more persistent fever pattern rather than the typical sJIA quotidian fever pattern.

Viral and postinfectious arthritis — Postinfectious and viral arthritis often present with fever that is not intermittent, rash that generally differs in appearance from that of sJIA, and transient arthritis. Parvovirus B19 is a commonly confused viral infection that causes arthritis, fever, and rash. The mistaken diagnosis of these self-limited conditions as sJIA may be responsible for the notion that sJIA can resolve completely without aggressive therapy. (See "Viral arthritis: Causes and approach to evaluation and management".)

Reactive arthritis, which can cause fever, may also follow a variety of infections. Those typically associated with fever, rash, and arthritis include neisserial and streptococcal infections as well as enteric infections. Rheumatic fever is an important differential diagnosis when it presents with fever and arthritis. However, when pericarditis is present, it is associated with endocarditis in this condition, the fever is often low grade, and both the arthritis and fever usually respond dramatically to nonsteroidal antiinflammatory drug (NSAID) treatment. Subacute bacterial endocarditis may also present with fever, rash, and arthritis and may be associated with a positive test for rheumatoid factor (RF) (see 'Laboratory findings' above). These entities can usually be differentiated by their clinical picture, appropriate culture results, and response to antibiotics. (See "Acute rheumatic fever: Clinical manifestations and diagnosis" and "Reactive arthritis" and "Clinical manifestations and evaluation of adults with suspected left-sided native valve endocarditis".)

Other autoimmune and autoinflammatory diseases — Arthritis with fever and rash may be the presenting manifestations in inflammatory bowel disease (IBD), Kawasaki disease (KD), systemic lupus erythematosus, polyarteritis nodosa, mixed connective tissue disease (MCTD), dermatomyositis, sarcoidosis, Behçet syndrome, and neonatal-onset multisystem inflammatory disease and other autoinflammatory diseases. These illnesses can usually be excluded by the clinical picture and appropriate laboratory evaluations. As an example, abdominal pain is common in polyarteritis nodosa and should prompt consideration of this illness once other causes have been excluded. Chronic abdominal pain in a child with suspected sJIA should not be ascribed to benign conditions, such as "mesenteric adenitis," without a thorough investigation to exclude other possible diagnoses, especially vasculitis and IBD. Early-onset sarcoidosis can present with fever, nonevanescent rash, and boggy synovitis as well as uveitis, which is not usually seen in sJIA. (See "Childhood-onset systemic lupus erythematosus (SLE): Clinical manifestations and diagnosis" and "Vasculitis in children: Incidence and classification", section on 'Polyarteritis nodosa' and "Juvenile dermatomyositis and other idiopathic inflammatory myopathies: Epidemiology, pathogenesis, and clinical manifestations" and "Overview of extrapulmonary manifestations of sarcoidosis", section on 'Musculoskeletal' and "Cryopyrin-associated periodic syndromes and related disorders" and "The autoinflammatory diseases: An overview".)

Multisystem inflammatory syndrome in children — Multisystem inflammatory syndrome in children (MIS-C) represents a potentially life-threatening episode of systemic inflammation that usually occurs four to six weeks after a primary infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and typically presents with fever, rash, and elevated acute-phase reactants. However, other common features of MIS-C, including hematologic involvement (thrombocytopenia and lymphopenia), gastrointestinal involvement, mucositis and conjunctivitis, and cardiac dysfunction progressing to shock, are not commonly seen in sJIA. Notably, arthritis is not often seen in MIS-C [23]. (See "COVID-19: Multisystem inflammatory syndrome in children (MIS-C) clinical features, evaluation, and diagnosis".)

Malignancy — Pediatric rheumatologists are commonly referred children thought to have sJIA who were then found to have leukemia, lymphoma, or other malignancies. Clinician awareness is the key to proper diagnosis. Refusal to weight bear is an important sign (red flag) of bone pain that may be indicative of a malignancy. sJIA is not associated with thrombocytopenia, lymphocytosis, neutropenia, or bone pain. Children with sJIA are uncomfortable and may have swollen and painful joints, but they rarely have exquisitely tender joints and/or bones and are usually able to walk short distances even though they have a limp [24]. By comparison, children with leukemia or other malignancies may have trouble simply bearing weight because of pain and may have severe pain when the shaft of a long bone is carefully palpated and compressed in locations away from the joints (eg, mid-humerus or mid-femur). The pain and joint swelling associated with leukemia can also change and be fleeting, as opposed to the pain of chronic arthritis, which usually does not move from place to place. (See "Evaluation of the child with joint pain and/or swelling" and "Overview of common presenting signs and symptoms of childhood cancer".)

Malaria — Malaria may have a diurnal fever pattern identical to that of sJIA and is also associated with chills, joint pains, and evidence of systemic illness. Malaria is extremely rare in nonendemic countries, but appropriate thick blood smears to exclude this diagnosis should be performed if the patient gives a history of residence in or travel to such areas. (See "Malaria: Clinical manifestations and diagnosis in nonpregnant adults and children".)

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: Juvenile idiopathic arthritis".)

SUMMARY AND RECOMMENDATIONS

●Clinical features – Systemic juvenile idiopathic arthritis (sJIA, formerly called Still's disease or systemic juvenile rheumatoid arthritis) is officially a subset of JIA that presents with spiking fevers (figure 1), evanescent rash (picture 1 and picture 2), and arthritis. However, sJIA is more similar to an autoinflammatory disorder and may be different from other categories of JIA. Presenting clinical features and laboratory abnormalities are reviewed in the table (table 1). (See 'Introduction' above and 'Overview' above.)

●Barriers to diagnosis – sJIA can be difficult to diagnose because there are no specific diagnostic tests, and arthritis, which is necessary for definite diagnosis, is often not evident early in the course of the disease. In addition, infection, malignancies, and other diagnoses must be considered prior to the diagnosis of sJIA because these patients can present similarly with fever, rash, and joint pain. (See 'Overview' above and 'Clinical manifestations' above and 'Laboratory findings' above and 'Diagnosis' above and 'Differential diagnosis' above.)

●Diagnosis – The diagnosis is made clinically and is based upon the presence of intermittent, daily, high, spiking fevers (in a quotidian fever pattern); typical evanescent rash; and arthritis, as well as the typical laboratory findings of granulocyte predominant leukocytosis, elevated acute-phase reactants including thrombocytosis and hyperferritinemia, and exclusion of other diagnoses, but there are no specific diagnostic tests. (See 'Diagnosis' above and 'Laboratory findings' above and 'Clinical manifestations' above.)

●Differential diagnosis – The differential diagnosis includes arthritis associated with infections, other autoimmune and autoinflammatory disorders, malignancy, and malaria. (See 'Differential diagnosis' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Thomas JA Lehman, MD, who contributed to earlier versions of this topic review.