49yo woman, with a history of hypertension and GERD, presents to your clinic with a six month history of bilateral shoulder weakness that she first noticed when putting on sweaters and jackets and carrying in groceries. She denies any history of pain, repetitive trauma, or weakness in the hands. On physical examination, she has 3.5/5 strength in shoulder abduction and flexion, as well as the below rash. She reports the rash has been present for about the same time, but doesn’t really bother her.
- What lab is likely to be profoundly elevated and what lab is most specific to this condition?
- What is the most likely diagnosis?
- Due to the inflammatory myopathy, muscle enzymes are often extremely elevated and are helpful in initial screening. Creatine kinase (CK) is most commonly ordered, but lactate dehydrogenase (LDH), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) are often elevated as well. The most common myositis-specific autoantibody is Anti-Jo 1 with others being Anti-SRP and Anti-MI-2.
- Given this history and dermatologic “shawl sign”, dermatomyositis is most likely. Polymyositis does not present with skin findings.