How would you approach evaluation and treatment of a patient on pembrolizumab therapy who presents with symmetric, proximal, upper extremity and lower extremity painful weakness without an elevated CK?   

Pembrolizumab, like other checkpoint inhibitors, is associated with a number of immune mediated neuromuscular syndromes including GBS/CIDP, a myasthenic syndrome, and myositis. A patient with symmetric proximal weakness and normal CK could have any of the above conditions. Normal CK does not exclude...