Clinical Reasoning: A 57-year-old man with subacute gait difficulty and hand tremor.

SECTION 1 A 57-year-old man presented with progressive difficulty in walking for 2 weeks, resting hand tremors for 1 week, and low-volume speech for 2 days. Initially, he had difficulty in initiation of walking. Soon, he developed shortstepped gait with history of en bloc falling forward. Within 2 weeks of the onset of illness, he became bedbound. While in bed, he remained very stiff and could not sit or turn sides by himself. He also had tremors in his upper limbs on action. His speech volume was reduced, but he always remained coherent. There was no bowel or bladder involvement, flexor spasms, or zonesthesia. The patient had been treated for ankylosing spondylitis (AS) with nonsteroidal anti-inflammatory drugs for 4 years because of low back pain, progressively increasing stooped-forward gait, and sclerosis of sacroiliac joints on X-ray. On examination, he had a masklike face. His blink rate was 1 to 4 blinks per minute. His Mini-Mental State Examination score was 29 of 30. He had hypophonic monotonous speech. His eye movements showed slow saccades and broken pursuit movements. Examination of motor system revealed normal muscle bulk, cogwheel rigidity of the upper limbs, and lead-pipe rigidity in the legs. His strength could not be tested because of profound muscle stiffness. Coarse action tremors were noticed in both hands. The patient had fixed-flexion deformity at the hip joint. Deep tendon jerks could not be elicited because of profound muscle rigidity. Plantar responses and abdominal reflexes also could not be elicited.