This week’s edition of the Step 1 Question of the Week is about musculoskeletal. See if you can answer the question and then watch the video to learn the correct answer as well as the rationales for each option.
A 65-year-old man comes to the physician with worsening weakness over the past several months. He says he has difficulty climbing stairs and opening jars. He eats a normal diet. When asked to stand, he uses his hands to lift off the chair. Serum studies show potassium of 5 mg/dL, thyroid-stimulating hormone of 4 mIU/L, and creatine kinase of 500 U/L. Erythrocyte sedimentation rate is 15 mm/hr, and C-reactive protein is 32 mg/dL (reference range: 0.8-100 mg/dL). Biopsy of the quadriceps muscle shows rimmed vacuoles, endomysial inflammation, and myofiber degeneration with amyloid deposition.
Which of the following is the most likely diagnosis?