Etiology of Erythrasma
Erythrasma is caused by Corynebacterium minutissimum, a lipophilic, filamentous, gram-positive bacillus that is part of normal skin flora. 1, 2
Causative Organism
- Corynebacterium minutissimum is a diphtheroid bacterium that colonizes the stratum corneum and releases porphyrins, which produce the characteristic coral-red fluorescence under Wood's lamp examination 1, 3
- This organism is a normal inhabitant of skin flora but becomes pathogenic under specific environmental conditions 1
Predisposing Factors and Risk Conditions
The development of erythrasma requires both the presence of the organism and favorable environmental conditions:
Environmental Factors
- Warm, moist, occluded intertriginous areas provide the ideal environment for C. minutissimum proliferation 1, 3
- The bacterium's lipophilic nature allows it to thrive in areas with increased sebum and moisture 1
- Hot seasons are associated with increased presentation of erythrasma 4
Host Factors
- Diabetes mellitus is a significant risk factor, with erythrasma being more common in diabetic patients than in the general population 2
- Obesity creates skin fold environments with moisture retention and compromised local defenses that favor bacterial growth 1
- Excessive sweating (hyperhidrosis) contributes to the warm, moist conditions necessary for infection 2
Anatomical Distribution
The infection preferentially affects specific body regions:
- Intertriginous areas including axillae, inguinal folds, inframammary regions, intergluteal folds, and crural folds 2, 3
- Interdigital spaces of the feet, where C. minutissimum is the most common cause of interdigital foot infections 2, 5
- The fourth interdigital web space is most commonly affected in pedal erythrasma 5
Coinfection Considerations
- C. minutissimum can coexist with dermatophytes or Candida albicans at the same cutaneous site, complicating diagnosis and treatment 2, 5
- In one study of interdigital erythrasma, 62.5% of cases had positive mycology with concurrent fungal organisms including Candida (16.6%), dermatophytes (12.5%), and Trichosporon (4.1%) 5
Clinical Pitfalls
- Erythrasma is frequently misdiagnosed as a dermatophytic infection, leading to underestimation of its true prevalence 4
- The condition may persist if treated with antifungal agents alone when bacterial infection is the primary pathology, though interestingly, some antimycotic agents show efficacy against erythrasma 4
- Wood's lamp examination showing coral-red fluorescence is pathognomonic and provides rapid, definitive diagnosis without need for culture 5, 3