Anti-MDA-5 negative, anti-Ku positive clinically amyopathic dermatomyositis.

We present a patient with anti-MDA5 negative, anti-Ku positive clinically amyopathic dermatomyositis (CADM). A 61-year-old woman presented with a chief complaint of a 20-year history of a pruritic rash that was active on her face, chest, hands, legs, and back. A mildly scaly, erythematous, photo-distributed eruption along with slightly violaceous, scaly papules accentuated on the wrist, metacarpophalangeal joints, proximal interphalangeal and distal interphalangeal joints. Antibody profile was significant for positive ANA and anti-dsDNA, elevated anti-TIF-1gamma (RDL)/p155, and weakly positive anti Ku. Biopsy was consistent with dermatomyositis. Melanoma differentiation-associated gene 5 antibody (anti-MDA-5) has been identified as the most commonly associated autoantibody found in CADM and is associated with poor prognosis and a biomarker for the diagnosis of rapidly progressive interstitial lung disease. To our knowledge, our patient is the first case of negative anti-MDA-5 and anti-Ku positive CADM.