Clinically amyopathic dermatomyositis associated with anti-MDA5 antibody

Clinically amyopathic dermatomyositis (CADM) is a rare entity that presents with cutaneous manifestations of classic dermatomyositis but without muscle weakness or abnormal muscle enzymes. It is more common in young white and Asian females. A subset of patients with CADM has a specific antibody known as anti-MDA5. These patients have a more aggressive course with distinct cutaneous features, pulmonary involvement and early death. Here, we present the case of a 64-year-old Caucasian male with no significant medical history who was admitted with marked weight loss and a painful rash for 6 months. Patient had no muscle weakness and his rash was characteristic of classic dermatomyositis. Skin biopsy was suggestive of dermatomyositis but muscle enzymes were normal. His serum was positive for anti-MDA5 antibody. Extensive workup failed to detect any malignancy but he did show non-specific interstitial pneumonia. He was treated with prednisone and mycophenolate with good clinical response.