Histopathologic Features of Acral Skin Biopsies in Dermatomyositis Patients and Comparison to Histopathologic Features in Non-Acral Biopsies.

BACKGROUND

Acral lesions may represent the best/only skin lesions to biopsy in patients suspected to have dermatomyositis (DM). However, histopathologic features of acral DM skin lesions are poorly characterized.

METHODS

We reviewed 50 acral biopsies from 46 DM patients and assessed numerous histopathologic features. The majority of biopsies (42/50; 84%) were sampled from either Gottron papules or signs. We compared histopathologic features in acral biopsies to those in 197 non-acral DM skin biopsies. We also compared histopathologic features in acral biopsies based on the presence of various clinical features.

RESULTS

Interface dermatitis, dyskeratotic keratinocytes, and superficial perivascular inflammation were common in DM acral biopsies. However, the absence of > 1 hallmark histopathologic feature (interface dermatitis, dyskeratosis, dermal mucin) was relatively common (56%). The presence of all three hallmark histopathologic features was significantly more likely in non-acral compared with acral DM biopsies (68% vs. 44%; p = 0.0021). The hallmark histopathologic feature most commonly lacking in acral compared with non-acral biopsies was increased dermal mucin. Histopathologic features in acral biopsies did not significantly differ based on acral location, DM subtype, therapeutic regimen, or myositis-associated/myositis-specific antibody status.

CONCLUSIONS

Pathologists should recognize that acral biopsies in DM patients may lack hallmark histopathologic features commonly seen in biopsies from non-acral locations.