A superficial, localized, mild and often chronic skin infection caused by corynebacterium minutissimum.  The organism’s growth is favored by moist, occluded intertriginous areas, including groin, axilla, intergluteal fold, and inframammary and periumbilical areas.  Lesions are irregular in shape and size, red, well defined patches covered with fine scales and wrinkling.  With time, the red color fades to brown.  Most lesions are asymptomatic, but mild pruritis may be present. 

A disciform variant exists which occurs outside the classically involved interriginous areas.  This generalized form is most commonly seen in diabetics, and can often be the presenting manifestation of type II diabetes.  The interdigital variant is the most common bacterial infection of the foot.  It frequently presents as a symptomatic, chronic maceration with fissuring or scaling of interspaces. 

Erythrasma begins as a proliferation of C. minutissimum within the stratum corneum.  Organisms can be found both extracellularly and intracellularly.  Whether the associated scale precedes and allows the corneum is still a matter of debate.  Predisposing factors include a warm, advanced age and compromised host status.  Erythrasma is much more common in adults than in children. 

The bright coral red flurorescence under a Wood’s light-the result of porphyrin production by the bacteria is the best way to make the diagnosis.  Tinea versicolor may resemble erythrasma but does not tend to localize to body folds.  Erythrasma can frequently mimic tinea cruris and candidiasis on the inner thighs, or in the groin and pubic area.  However, erythrasma is not associated with satellite lesions, vesiculation, or much inflammation.  Coral red fluorescence under Wood’s light will distinguish tinea pedis from interdigital erythrasma.  Mycological examination of the scales or empiric treatment of tinea may be warranted, as a co-infection is very common.  Disciform erythrasma can be differentiated from lichen sclerosus and plaque type parapsoriasis by Wood’s light examination.  

Original text