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.