The diagnostic approach in a patient with possible myopathy begins with a history and physical examination, followed by the blood tests: creatine kinase (CK), thyroid function tests, chemistries including calcium and phosphorus, vitamin D, parathyroid hormone, antinuclear antibodies, erythrocyte sedimentation rate, HIV antibody, lactate, pyruvate, serum protein electrophoresis and immunofixation, and acid maltase levels. In patients with suspected inflammatory myopathy, myositisspecific, or myositis-associated antibodies may be checked. Patients with myopathy may show typical small, brief, and polyphasic motor unit action potentials (MUAPs) with early recruitment uniformly in all sampled muscles. The neurophysiologic study of a patient with possible myopathy may begin with sensory and motor nerve conduction studies to rule out a neuropathic process or a concomitant neuropathy in a patient with myopathy. The needle electromyography (EMG) examination of patients with myopathy may be normal or abnormal.