A 39-year-old woman comes to the physician for a 2-month history of progressive weakness and tingling of her hands. She has a 15-year history of rheumatoid arthritis managed with multiple medications. Examination shows 3+ deep tendon reflexes in the upper extremities. Which of the following is the most appropriate next step in diagnosis?
Measurement of serum creatine kinase activity
X-ray of the hands
DEXA scan
Electromyography and nerve conduction studies
Serum methotrexate levels
MRI of cervical spine
