A histopathologic study of mechanic's hands associated with dermatomyositis: a report of five cases.

Background  Mechanic's hand is a defined specific skin eruption associated with dermatomyositis; there are few reports concerning its histopathology. As mechanic's hand clinically resembles hand eczema, it is important to distinguish between these two conditions. Aim  To determine the characteristic clinical and histopathologic features of mechanic's hand, and to clarify whether these two conditions can be differentiated by histopathologic findings. Methods  We analyzed clinicopathologically five patients with mechanic's hands who visited our clinic between 2006 and 2007. Results  The clinical features of mechanic's hands were discrete hyperkeratotic erythema on the ulnar aspect of the thumbs and the radial aspect of the fingers. In all five cases, the histologic findings included marked hyperkeratosis, focal parakeratosis, psoriasiform acanthosis, and colloid bodies in the epidermis. There were mononuclear cell infiltrates around the blood vessels, and mucin deposition was observed in the dermis. Conclusions  The histopathologic findings of mechanic's hands are specific and different from those of eczema. A histopathologic examination is useful for the diagnosis of mechanic's hands associated with dermatomyositis and a high incidence of interstitial pneumonia.