Increased histological severity and chronicity of interface inflammation in anti-MDA5 dermatomyositis-A comparative dermatopathological analysis.

Anti-melanoma differentiation-associated gene 5 (MDA5) dermatomyositis is characterized by serological detection of anti-MDA5 antibody and rapidly progressive interstitial lung disease. In this study, the largest cohort of skin biopsies to date of anti-MDA5 dermatomyositis was reviewed and compared with cases of dermatomyositis with negative serology. Findings contribute to the histological diagnosis and evaluation of the severity of cutaneous inflammation in anti-MDA5 dermatomyositis. Skin biopsies collected over a 7-year period from individuals with clinically and histologically confirmed dermatomyositis with anti-MDA5 serology were reviewed. A total of 46 cases with 17 anti-MDA5 positive cases were retrieved. Patients with positive antibody were younger (53.7 vs. 60.6 years, p = .013). No differences in epidermal changes (p > .05) were observed. Pertaining to interface changes, anti-MDA5 dermatomyositis showed a higher degree of pigmentary incontinence (p = .014), suggesting increased and sustained cutaneous inflammation. Periodic acid-Schiff (PAS) stain demonstrated a greater degree of basement membrane thickening (p = .045). Other parameters, including dermal inflammation, dermal mucin deposition and vasculitic/vasculopathic features did not show statistical difference between anti-MDA5 positive and negative dermatomyositis (p > .05). Findings suggest increased cutaneous inflammation for anti-MDA5 dermatomyositis. In skin biopsies, marked pigmentary incontinence or basement membrane thickening should raise suspicion of anti-MDA5 dermatomyositis.