Erythrasma is a common skin disorder caused by bacteria. It was first described in 1859 by Burchardt. He thought the etiology was fungal. In 1862, Burchardt's teacher, Von Barensprung coined the term erythrasma and named the bacteria Microsporum minutissimum. Today, it is known to be caused by Corynebacterium minutissimum. Corynebacterium is gram-positive, catalase-positive, non-spore forming.
Erythrasma causes itching. It creates a scaling and erythema. It is often asymptomatic.
In 1961, Sarkay et al. examined scrapings from scales of an erythrasma lesion by microscopy. He described it as gram-positive rods which were found to be C. minutissimum. The bacteria have also been shown to cause severe disease in immunocompromised patients including cutaneous fistulas, granulomatous lesions, and subcutaneous abscesses. Corynebacterium is a commensal skin bacteria. Partly due to the potential for serious complications in immunocompromised hosts, C. minutissimum has had its genome sequenced by organizations within the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.
Other environmental and host factors that increase the risk of erythrasma are living in a humid environment, excessive sweating, coexisting skin disorders, and obesity.
Most erythrasma occurs in healthy adults. It occurs less often in children. It tends to be more prevalent in hot and humid climates. Individuals who live in institutions are also more likely to develop erythrasma. This includes college students in dorms, soldiers in barracks, and senior adults in nursing facilities. Erythrasma incidence may increase in age. It may occur more often in males. It occurs worldwide.
Under conditions of moisture and occlusion, C. minutissimum grows in the upper levels of the stratum corneum. It produces a coral red fluorescence on Wood's light exam because of coproporphyrin III.
A biopsy is rarely needed for diagnosis of erythrasma. Examination of the skin by microscopy would show rod-like organisms in the horny layer. However, these are sometimes missed. There may also be coccoid forms. There will be hyperkeratosis with some lymphohistiocytic infiltrate around the vasculature of the top layer of skin.
Gram stain shows gram-positive rods. If C. minutissimum is left for long on the culture plate, the cultures become gram-negative and of varying shapes. C. minutissimum is not acid fast. It produces acid from dextrose, sucrose, and maltose, but not lactose. It has been proven to be sensitive to erythromycin in vitro but resistant to penicillin. It is difficult to visualize the organism on hematoxylin and eosin-stained slides and may be better visualized with Periodic Acid-Schiff and Giemsa stains.
Erythrasma is most commonly observed in the toe webs followed by the groin. It is less seldom found in the axilla. Patients may give you a history of slightly itchy skin discoloration in any of those areas. Patients may also complain of scaling skin.
C. minutissimum is the most common cause of bacterial infection of the interdigital spaces of the feet. It will cause maceration and scaling. It most often occurs in between the fourth and fifth toes. It is mostly asymptomatic but can be pruritic. It does occur occasionally with dermatophyte or candidal infections. A KOH prep may be necessary to assess for coexisting infection.
Also either mildly pruritic or asymptomatic. It occurs as patches or plaques in intertriginous areas and results in a "cigarette paper" appearance of the skin. It may have a fine scale.
A rare form of erythrasma that may affect any part of the body. It is more often seen in black women in tropical climates. It is characterized by well defined scaly plaques on the trunk and proximal parts of the limbs that have coral red fluorescence under Wood's lamp.
A Wood's lamp does help in the diagnosis of erythrasma. However, if no lamp is available, it is reasonable to start empiric treatment based on the exam.
Wood's lamp is useful in diagnosing erythrasma. Biopsy of suspected erythrasma sometimes shows the rod-like organisms. However, these are often difficult to observe, and the biopsy specimen may require Giemsa stain or Acid-Schiff stain. This makes biopsy somewhat impractical for diagnosis.
Erythrasma responds to topical and oral therapies, but it often reoccurs. Topical therapies include fusidic acid, clindamycin, or erythromycin. Fusidic acid is an antibiotic that is not available in the United States. It acts by blocking aminoacyl-tRNA transfer to protein in susceptible bacteria. It was compared to oral erythromycin and clarithromycin in a double-blind placebo-controlled, randomized study at the University Hospital in Izmir, Turkey. It enrolled 151 adults over age 18 and divided them into five groups: group one got a single dose of 1 gram of oral clarithromycin, group 2 got 1 gram per day of oral erythromycin for 14 days, group 3 got placebo tablets for 14 days, group 4 got topical fusidic acid cream 2% twice a day for 14 days, group 5 got placebo cream twice a day for 14 days. The fusidic acid cream was found to be superior to oral clarithromycin and erythromycin in reducing Wood's lamp scores. The score was based on the intensity of coral red fluorescence. This was thought to be due to the ability of a fusidic acid to remove coproporphyrin III from the stratum corneum. Fusidic acid was also found to cause a complete clinical response in 96% of patients, while clarithromycin caused the same response in 66% of patients and erythromycin 53% of patients.
Extensive erythrasma requires oral therapy. Oral options include clarithromycin 1 gram for a one time dose. Oral erythromycin 1 gram per day (in divided doses) for 14 days is also an option.
Clarithromycin has some advantages over erythromycin in that it can be given as a single dose. Clarithromycin is a macrolide that inhibits protein synthesis by binding to the 50s ribosomal subunit of the bacteria. It has better bioavailability than erythromycin due to a hydroxy to O-methyl substitution at position 6 on the lactone ring. It may be more effective in treating erythrasma in the groin. There have been few comparative studies between erythromycin and clarithromycin.
Side effects and adverse effects of both oral options listed above include nausea, abdominal pain, hearing loss, metallic taste, ventricular arrhythmias, cholestatic jaundice, and toxic epidermal necrolysis.
The following should be considered in the differential for erythrasma:
Seborrheic dermatitis involves greasy and erythematous lesions along the scalp and nasolabial folds. Inverse psoriasis has a shiny appearance. The coral red fluorescence with Wood's lamp exam helps distinguish erythrasma from seborrheic dermatitis and inverse psoriasis. KOH prep may be required to distinguish erythrasma from dermatophytosis of the toe webs. Erythrasma of the groin is easily distinguished from tinea cruris due to the scaling border of tinea cruris.