A 50 year old male presents with a 3 month history of fatigue and progressive weakness, predominantly affecting the proximal muscles of the arms and legs. There are associated myalgias and arthralgias. He has lost 8kg in the past 2 months. He is having difficulty rising from a seated position or raising his arms to wash his hair. He has noticed difficulty with swallowing, and frequently coughs when drinking liquids. Blood work demonstrates an elevated CK of 1374.
You are concerned that the patient has an inflammatory myopathy, but what other conditions should be considered in the differential of an elevated CK?