A 50-year-old man complains of weakness. His
symptoms began as difficulty with buttoning his shirt and
using keys to open doors about 2 years ago. He was
treated empirically with nonsteroidal anti-inflammatory
medications for arthritis, but responded only minimally.
His symptoms have slowly progressed to the point where
he has weakness in both hands and feet. He avoids going
outside because of frequent falls. On examination, he has
weakness and atrophy of the foot extensor and finger flexors.
Proximal muscle strength is normal. Reflexes are normal,
and sensation is intact. He is able to rise out of a
chair, but the Romberg test is not able to be performed
due to weakness once standing. Cranial nerves are intact.
Serum creatine kinase is 600 U/L. Complete blood count,
differential, electrolytes, and thyroid-stimulating hormone
(TSH) are normal. Based on the clinical presentation,
what is the most likely diagnosis?
A. Dermatomyositis
B. Eosinophilic myofasciitis
C. Inclusion body myositis
D. Polymyositis
E. Hyperthyroidism