43yo 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?