Pseudocheckerboard pattern: an interesting histopathological finding in mechanic's hands

Mechanic's hands are a well-known symptom often associated with dermatomyositis and are similar to hand eczema clinically. Histopathology of them usually shows hyperkeratosis, focal parakeratosis, psoriasiform acanthosis, basal vacuolar changes and necrotic keratinocytes in the epidermis and upper dermal mucin deposition. However, there have been few comparative histopathologic evaluations of mechanic's hands and palmoplantar eczema.

We evaluated the histopathology of mechanic's hands in 6 patients with dermatomyositis who visited our hospital between 2006 and 2014 comparing with histopathology of 27 patients with palmoplantar eczema, retrospectively.

As previously reported, hyperkeratosis, basal vacuolar change and necrotic keratinocytes were seen in all cases of mechanic's hands. Basal vacuolar change was not observed in any cases of palmoplantar eczema. Three cases of mechanic's hands demonstrated a characteristic finding, a pseudocheckerboard pattern, in the hyperkeratotic horny layer; there were areas of alternating parakeratosis and orthokeratosis in a vertical arrangement and these areas alternated with the completely orthokeratotic areas in a horizontal arrangement. This pattern has not been focused in mechanic's hands so far. Same pattern was also observed in four patients with palmoplantar eczema.

'Pseudocheckerboard pattern' was not specific but may be a possible diagnostic clue for mechanic's hands.