Erythrasma

INTRODUCTION — Erythrasma is a superficial infection of the skin caused by Corynebacterium minutissimum, a gram-positive, non-spore-forming bacillus (picture 1). The disorder typically presents as macerated, scaly plaques between the toes or erythematous to brown patches or thin plaques in intertriginous areas (picture 2A-G).

The epidemiology, clinical manifestations, diagnosis, and treatment of erythrasma will be discussed here.

EPIDEMIOLOGY AND RISK FACTORS — Erythrasma is a common disorder. However, the prevalence is difficult to assess since many patients do not seek treatment or have subclinical infection. In a 1970 study of 754 college students in the United Kingdom, 19 percent had erythrasma [1]. A subsequent study of patients seen in a New Zealand dermatology clinic found a prevalence of 20 percent [2]. Higher prevalences have been reported in soldiers and institutionalized patients [3,4].

Erythrasma often occurs in healthy adults [1], but diabetic patients, older adults, or immunocompromised patients have increased risk for the disorder [5]. Conditions predisposing to skin occlusion and moisture also contribute to erythrasma, including obesity, hyperhidrosis, and living in tropical climates. There are reports of erythrasma in patients with active hidradenitis suppurativa [6]. Erythrasma is rare in children [7].

PATHOGENESIS — Erythrasma is caused by C. minutissimum, a component of the normal skin flora. C. minutissimum is a gram-positive, non-spore-forming, aerobic or facultative bacillus [8]. Under conditions of moisture and occlusion, C. minutissimum proliferates in the upper levels of the stratum corneum.

Corynebacteria may also cause trichomycosis axillaris (picture 3) and pitted keratolysis (picture 4) [7]. The coexistence of erythrasma, pitted keratolysis, and trichomycosis axillaris has been documented [9].

CLINICAL PRESENTATION — Erythrasma most commonly involves the toe webs, followed by the groin and axilla. In one study of college students, 85, 16, and 10 percent of students had interdigital, groin, or axillary disease, respectively [1]. Another study involving institutionalized patients showed a similar trend; 70 percent of patients with erythrasma had pedal interdigital disease, 42 percent had groin disease, and 36 percent had axillary disease [3].

Interdigital — Erythrasma is the most common cause of interdigital bacterial infection on the feet. This variant exhibits scaling and maceration of the web spaces (picture 2A-B), usually between the fourth and fifth toes. Interdigital erythrasma may be asymptomatic or pruritic. Interdigital erythrasma may occur concomitantly with dermatophyte or candidal infection [2,10].

Intertriginous — Intertriginous erythrasma exhibits well-defined, erythematous patches or thin plaques in the axillae, inframammary region, umbilicus, or groin (picture 2C-G). With time, the initial reddened color changes to brown. Involved areas often have visible fine scale and wrinkling that gives the skin a "cigarette paper" appearance. Affected areas are asymptomatic or mildly pruritic.

Disciform — A rare disciform variant of erythrasma consists of generalized, round plaques not confined to intertriginous areas (picture 5) [11]. Disciform erythrasma has been reported to occur more frequently in Black women who live in tropical climates [11].

Genital/perianal — Erythrasma is an occasional cause of chronic pruritus ani [12]. (See "Approach to the patient with anal pruritus".)

Rarely, erythrasma may affect the vulva, causing chronic pruritus that may mimic candidal infection [13,14].

DIAGNOSIS — The diagnosis of erythrasma is based upon physical appearance and the presence of coral-red fluorescence with a Wood's lamp. A Gram stain, culture, or biopsy can confirm the diagnosis, but usually is not necessary.

If a Wood's lamp examination or other confirmatory tests are not feasible but there is a high clinical suspicion for erythrasma, it is reasonable to initiate empiric treatment with a topical agent. (See 'Treatment' below.)

Physical examination — Interdigital scaling and maceration should raise suspicion for interdigital erythrasma, and well-defined erythematous or brown patches or thin plaques in intertriginous areas should raise suspicion for the intertriginous variant.

A Wood's lamp examination depicting coral-red fluorescence confirms the diagnosis of erythrasma (picture 6). This fluorescence is due to the production of porphyrins by C. minutissimum. A false negative test may occur if the patient has bathed soon before the examination, since porphyrins are water-soluble and can be washed away [13]. (See "Office-based dermatologic diagnostic procedures", section on 'Wood's lamp examination (black light)'.)

Gram stain — Gram stain of a skin scraping will reveal gram-positive filaments and rods, consistent with detection of C. minutissimum (picture 1).

KOH preparation — For patients with interdigital involvement, a potassium hydroxide (KOH) preparation of a skin scraping is suggested to assess for concomitant dermatophyte infection [10,15]. (See 'Interdigital' above and "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)

Other tests — Although rarely indicated, the bacterium can be cultured on media containing 20% fetal bovine serum, 2% agar, and 78% tissue culture medium 199 [16].

C. minutissimum can also be seen on skin biopsy (picture 7). The organism is difficult to detect on hematoxylin- and eosin-stained slides; visualization may be enhanced by use of special stains such as periodic acid-Schiff and Giemsa.

DIFFERENTIAL DIAGNOSIS — Other dermatologic diagnoses have clinical features similar to erythrasma, for example:

●Seborrheic dermatitis (picture 8) (see "Seborrheic dermatitis in adolescents and adults")

●Inverse psoriasis (picture 9) (see "Psoriasis: Epidemiology, clinical manifestations, and diagnosis", section on 'Inverse (intertriginous) psoriasis')

●Candidiasis (picture 10) (see "Intertrigo")

●Dermatophytosis (picture 11) (see "Dermatophyte (tinea) infections")

●Tinea versicolor (pityriasis versicolor) (picture 12) (see "Tinea versicolor (pityriasis versicolor)")

●Parapsoriasis (may resemble disciform variant) (picture 13) (see "Parapsoriasis (small plaque and large plaque parapsoriasis)")

●Pityriasis rotunda (may resemble disciform variant)

Seborrheic dermatitis and inverse psoriasis can mimic intertriginous erythrasma. Seborrheic dermatitis is suggested by the presence of erythema and greasy scale on the scalp, eyebrows, or nasolabial folds. Inverse psoriasis plaques tend to have a shinier appearance compared with erythrasma and may be accompanied by other manifestations of psoriasis. The characteristic coral-red fluorescence with Wood's lamp examination distinguishes erythrasma from these disorders.

Interdigital tinea pedis can be clinically indistinguishable from interdigital erythrasma [10]. A potassium hydroxide (KOH) preparation helps to identify dermatophytosis, tinea versicolor, and candidiasis. Although dermatophyte or candidal infections may coexist with erythrasma, a positive KOH preparation in the absence of coral-red fluorescence suggests an isolated fungal infection. Tinea cruris often exhibits an active scaling border, a clinical feature uncommon in erythrasma. (See "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)

Small plaque parapsoriasis and large plaque parapsoriasis are characterized by chronic, asymptomatic or mildly pruritic erythematous plaques that typically occur on the trunk and proximal extremities. (See "Parapsoriasis (small plaque and large plaque parapsoriasis)".)

Pityriasis rotunda is a rare disorder of keratinization characterized by multiple 2 to 10 cm, round to oval, hyperpigmented or hypopigmented plaques on the trunk or extremities [17]. Parapsoriasis and pityriasis rotunda may be differentiated from each other and from erythrasma by skin biopsy.

TREATMENT — Erythrasma responds to a variety of topical and oral therapies, although recurrence is common. Evidence supporting or comparing various treatments is limited. Treatment selection depends on the extent of disease and drug cost or availability. We recommend treatment with topical therapy for patients with limited skin involvement and suggest systemic therapy for patients with widespread disease.

Localized erythrasma — For patients with localized disease, topical therapy with antibacterial agents such as fusidic acid, clindamycin, or erythromycin is usually effective. Our first-line treatment is typically topical clindamycin or erythromycin; fusidic acid is not available in the United States. Limited data suggest that topical imidazole antifungal drugs also have activity against gram-positive bacteria, including C. minutissimum, and may effectively treat erythrasma [5,18]. Topical therapies are generally applied twice daily for two to three weeks.

Topical clindamycin or erythromycin — Topical clindamycin and topical erythromycin have been used for erythrasma for many years. Clinical experience supports the efficacy of these therapies [19].

Topical fusidic acid — Topical fusidic acid was highly effective when applied twice daily for up to two weeks in randomized trials and a small observational study [20,21].

Topical imidazole antifungal agents — In randomized trials of topical antifungal therapies that included small numbers of patients with erythrasma, treatment with oxiconazole, miconazole, tioconazole, or econazole twice daily for 7 to 60 days cleared more than 90 percent of erythrasma [18,22,23]. Once-daily treatment with oxiconazole was also efficacious [18].

Other topical therapies — Other topical therapies (mupirocin 2% ointment [24], Whitfield's ointment [5], topical benzoyl peroxide, and special antibacterial soaps [5]) have been reported as successful treatments, though efficacy data are limited. Given the high efficacy and tolerability of topical erythromycin and topical clindamycin, we do not typically treat with these agents. In particular, Whitfield's ointment may cause significant irritation on intertriginous skin, and the efficacy of benzoyl peroxide and commercially available antibacterial soaps is unclear.

Extensive erythrasma — It can be difficult to treat large body areas with topical therapies. Extensive disease may warrant oral therapy. We suggest clarithromycin (single 1 g dose for adults) or oral erythromycin (1 g per day [in divided doses] for 14 days for adults).

Clarithromycin or oral erythromycin — In a placebo-controlled randomized trial that assessed the efficacy of erythromycin (1 g per day for 14 days), a single 1 g dose of clarithromycin, and topical 2% fusidic acid (applied twice daily for 14 days) in adults with erythrasma, all treatments reduced Wood's light reflection scores compared with placebo [21]. Fusidic acid had the lowest reflection scores at day 14, and a significant difference in scores between patients treated with erythromycin and clarithromycin was not detected. A complete response (reflection score of 0) with the fusidic acid, clarithromycin, erythromycin, placebo cream, and placebo tablet groups were 97, 67, 53, 13, and 3 percent, respectively. Successful treatment with erythromycin or a single 1 g oral dose of clarithromycin has also been documented in case reports [13,25,26].

Oral erythromycin is usually given at a dose of 250 mg four times per day for 14 days for adults [5]. Gastrointestinal distress (nausea, diarrhea, abdominal pain) is a common side effect of therapy. Enteric-coated erythromycin (333 mg three times daily) may offset gastrointestinal side effects. Antibiotic resistance may occur in some patients who fail to respond to erythromycin, as reported in a study of 40 patients [27].

Other therapies — Tetracycline (250 mg four times per day for 14 days) has been used to treat erythrasma, although it may be less beneficial than erythromycin for intertriginous disease [5].

Photodynamic therapy (PDT) has been reported to improve erythrasma [28], but is not a recommended treatment. This technique takes advantage of the natural porphyrins produced by C. minutissimum. In a study that evaluated the effect of a red light-emitting PDT device in 13 patients with erythrasma, patients were reported to have a reduction in size of their erythrasma lesions, but less than 25 percent of the treated patients had complete clearance [28].

INDICATIONS FOR REFERRAL — Failure to respond to appropriate therapy may suggest that the diagnosis of erythrasma is not correct or that there is a concomitant underlying disease process. In these cases, referral to a dermatologist may be helpful.

PREVENTION — Affected patients should be examined for disease at other sites. Persistent disease in untreated sites may contribute to disease recurrence [5].

Occlusion and moisture contribute to the development of erythrasma; therefore, measures to minimize skin occlusion and moisture may help to prevent infection. Control of hyperhidrosis with aluminum chloride prevented the recurrence in one observational study [9].

Benzoyl peroxide or antibacterial soaps may be preventive treatments [29], but confirmatory data are lacking.

SUMMARY AND RECOMMENDATIONS

●Epidemiology and risk factors – Erythrasma is a superficial infection caused by Corynebacterium minutissimum. The disorder occurs in healthy adults, but individuals with diabetes mellitus or immunodeficiency may be at increased risk. (See 'Epidemiology and risk factors' above.)

●Clinical presentation – Interdigital disease is the most common presentation of erythrasma, characterized by scaly, macerated skin in the toe web spaces (picture 2A-B). Coinfection with dermatophytes or Candida may occur. Erythematous to brown patches or plaques in the axillae, inframammary areas, umbilicus, or groin characterize the intertriginous variant (picture 2C-G). Erythrasma is usually asymptomatic or mildly pruritic. (See 'Clinical presentation' above.)

●Diagnosis – The skin findings plus examination with a Wood's lamp revealing coral-red fluorescence confirms the diagnosis (picture 6). For patients with interdigital involvement, microscopic examination of a skin scraping with a potassium hydroxide (KOH) preparation helps to determine whether there is concomitant dermatophyte infection. (See 'Diagnosis' above and "Office-based dermatologic diagnostic procedures", section on 'Potassium hydroxide preparation'.)

●Treatment:

•Localized erythrasma – For patients with localized erythrasma, we recommend treatment with topical therapy (Grade 1B). Topical clindamycin, topical erythromycin, and topical fusidic acid are commonly used treatments. All are usually applied twice daily for 14 days. Topical fusidic acid is not available in the United States. (See 'Localized erythrasma' above.)

•Extensive erythrasma – For patients with more extensive involvement, we suggest treatment with oral clarithromycin or oral erythromycin (Grade 2B). (See 'Extensive erythrasma' above.)

ACKNOWLEDGMENTS — The UpToDate editorial staff acknowledges Mariah Brown, MD, and Sylvia Brice, MD, who contributed to earlier versions of this topic review.