A 69-Year-Old Woman with a Long History of Rheumatoid Arthritis

A 69-year-old woman with a long history of rheumatoid arthritis (RA) is brought to the physician by her daughter because of gait instability and near-falls.  She was previously able to walk outdoors with the use of a cane, but she has required a walker for the past three months.  She also notes that her mother has been holding onto the furniture when she walks from room to room.  The patient denies any new joint pain or discomfort, muscle pain, or numbness in her arms and legs.
The patient had RA treatment in the past with methotrexate.  She underwent right-sided knee replacement seven years ago. Recent x-rays of the replaced joints did not demonstrate any fractures or prosthesis loosening.  Her other medical problems include hypertension, hyperlipidemia, and lactose intolerance.  Her current medications include low-dose prednisone, ibuprofen, lisinopril, hydrochlorothiazide, simvastatin, calcium, and vitamin D.
Her blood pressure is 135/85 mm Hg supine and 130/90 mm Hg standing.  Her pulse is 85/min and regular.  Joint examination shows subluxation of the metacarpophalangeal joints and ulnar deviation bilaterally.  There is mild synovitis of both wrists.  Flexion is moderately restricted at the right hip.  The knees show full range of motion.  Motor strength is 4/5 in the proximal muscles of both upper and lower extremities.  Deep tendon reflexes are 3+ in both the upper and lower extremities bilaterally with a few beats of unsustained clonus at the ankles.  Her gait is unsteady.  She cannot walk heel-to-toe without assistance.  Proprioception is decreased at both ankles.
Which of the following is the most appropriate next step?

A) Check TSH and CPK levels
B) Order an MRI of the cervical spine
C) Refer to physical therapy for gait training
D) Start treatment with anti-TNF agents
E) Stop prednisone and re-evaluate in 2-4 weeks