Erythrasma
A superficial bacterial skin infection in body folds that causes red-brown patches and glows coral-red under a special ultraviolet light.
Emergency Management: None directly related to isolated erythrasma.
Erythrasma is a chronic, superficial bacterial infection of the stratum corneum of the skin, typically affecting the intertriginous (skin-fold) areas. It presents as well-demarcated, reddish-brown, slightly scaly patches.
Detailed Overview
Caused by the normal skin flora organism Corynebacterium minutissimum, erythrasma flourishes in warm, moist environments. It is most commonly found in the toe webs, groins, axillae, and submammary folds. It is often misdiagnosed as a fungal infection (tinea cruris or pedis), leading to treatment failure. The pathognomonic feature is its brilliant coral-red fluorescence under a Wood's lamp.
Epidemiology & Demographics
Common worldwide, but more prevalent in tropical or humid climates. Higher incidence in adults, obese individuals, and patients with diabetes mellitus.
Etiological Mechanism
Infection by Corynebacterium minutissimum, a gram-positive, non-spore-forming bacillus that normally resides on the skin but overgrows in favorable conditions.
Primary Causes
Overgrowth of bacteria due to maceration, occlusion, moisture, and altered host defenses.
C. minutissimum proliferates in the humid, occluded microenvironment of intertriginous spaces. It remains confined to the upper third of the stratum corneum and does not invade deeper living tissue. The bacteria produce coproporphyrin III, a porphyrin pigment that gives the lesions their characteristic brown hue and causes the striking coral-red fluorescence when exposed to ultraviolet light (Wood's lamp).
Diagnostic Criteria & Guidelines
Clinical appearance in typical locations, definitively confirmed by coral-red fluorescence under a Wood's lamp examination in a dark room. KOH preparation is negative for hyphae (unless co-infection is present).
Topical antibiotics are the standard of care. Clindamycin 1% lotion/gel or Erythromycin 2% solution applied BID for 7 to 14 days. Fusidic acid cream (outside the US) is also highly effective. Miconazole or Clotrimazole creams (which have some anti-gram-positive bacterial activity) can be used, especially if co-infection with fungus is suspected.
Second-Line & Adjunctive Therapy
For extensive, generalized, or refractory cases: Systemic antibiotics. Oral Erythromycin 250 mg QID for 14 days, or a single dose of Clarithromycin 1000 mg. (Note: Macrolide resistance is increasing, so Tetracyclines like Doxycycline 100 mg BID for 7-14 days can be used).
Surgical & Procedural Management
Not applicable.
Patient Counseling & Advice
Inform the patient that while the rash looks like a fungus, it is actually a bacteria, which is why their over-the-counter antifungal creams might not have worked well. Reassure them that the discoloration may take several weeks to fade completely even after the bacteria are dead.
Follow-Up & Monitoring Schedule
Re-evaluate in 2-4 weeks. If the rash persists, re-examine with a Wood's lamp (should be negative if cured) and perform a KOH prep to check for an unmasked fungal infection.
Preventive Strategies
Daily use of antibacterial soaps (e.g., chlorhexidine wash) in intertriginous areas. Thoroughly drying skin folds after bathing.
Excellent with proper antibacterial treatment, but recurrences are very common if underlying predisposing factors (obesity, poor hygiene, diabetes) are not addressed.