A man with tingling fingers

A 73 year old man with a three month history of bilateral persistent tingling in the index and middle fingers presented to his general practitioner. He was referred for an injection for suspected carpal tunnel syndrome. When he attended, as well as the tingling sensation, he described loss of fine motor function in his hands, with altered sensation in both legs and his inner thighs. Examination at this time showed no objective sensory loss in either hand. Phalen’s test and Tinel’s test were both negative. His upper limb tendon reflexes were normal. Because of his new motor and lower limb symptoms, his GP referred him to an outpatient neurology clinic. At the clinic, he said that he had first noticed his symptoms while gardening. The tingling in his fingers was now present constantly. When he bent down to tie his shoes it worsened in his arms and travelled down his back. Lately he had struggled to fasten buttons and was having trouble writing. He also had slight numbness in both legs. He denied loss of power or perineal numbness and had no bowel, bladder, or erectile problems. He had no medical history of note and was taking no drugs. On examination, his fundi and cranial nerves were normal. He had weakness of the right abductor pollicis brevis and abductor pollicis opponens muscles. Touch, pinprick, temperature, vibration, and proprioception were not impaired. With his arms outstretched and eyes closed, his fingers moved constantly. All his tendon reflexes were present and equal, including the supinators. His plantars were downgoing. Lower limb neurological examination demonstrated normal power, coordination, and sensation, except for an unsteady gait. A full blood count showed that he had macrocytic anaemia (mean corpuscular volume 118.9 fL; reference range 77-95; haemoglobin 102 g/L; 130-180). Magnetic resonance imaging was performed (figs …