Definition. A rare, mildly contagious, vegetable parasitic disease, caused by the microsporon minutissimum and characterized by reddish-brown patches on moist opposing surfaces.
Symptoms. Small, rounded, well-defined, erythematous or scaly macules which later become red or brown in color compose the initial eruption. The patches increase slowly and become irregular, rarely exceeding a silver dollar in size and are usually few in number. They are situated almost exclusively on the opposing folds of the axillary, genitocrural and inguinal regions or on surfaces near by, but may rarely extend from these warm moist parts to the thighs and arms. The disease may exist for years and hardly be noticed because itching is absent or very slight; because it causes no inconvenience to the patient its discovery is often accidental.
Etiology and Pathology. Erythrasma is rare in this country, but more common in France and Germany. It is an adult affection, more often found in men, and is caused by a vegetable organism somewhat similar to that of tinea versicolor, called the microsporon minutissimum. Its component parts, the mycelia and spores, are about one-third the size of the ringworm fungus, and are situated in the superficial part of the corneous layer. Unna says that these spores are not found in isolated collections but are irregularly scattered singly. A lens of 500 to 600 diameters is required to see this fungus.
Diagnosis. Tinea cruris (eczema marginatum) is distinctly inflammatory, with an elevated and advancing border and is often acute in its development. Tinea versicolor occurs on the trunk, rarely extending to the sites of erythrasma, and is not red in color. Pityriasis rosea has a typically short course and wider distribution. Chloasma is due entirely to increase of pigment and may be typically located. Both of the last-named diseases are nonparasitic and the microscope will aid in diagnosis.
Prognosis and Treatment. The disease is persistent and tends to relapse unless the fungus is entirely destroyed. The same measures of cure and prevention of relapse as suggested for tinea versicolor may be used here.