The case

A 68-year-old woman presented to the neurology rapid access clinic with a 6-month history of progressive unsteadiness and loss of dexterity. Her initial symptoms had been numbness and burning pain in the left leg, followed over several weeks by impaired sensation in the right leg, right arm and finally the left arm. She had been previously independent, but was now unable to walk or stand unaided. She also reported intermittent nausea and significant weight loss.

Just before the symptoms began, her general practitioner identified hyponatraemia while treating her for a chest infection. Four years before, a routine mammogram had shown a suspicious lesion, which was biopsied and reported as benign. Three years later, she declined the invitation for a recall mammogram. She was a longstanding smoker (∼75 g of tobacco per week). Her daughter had hypothyroidism and vitiligo and a grandson had autoimmune liver disease. Her mother had valvular heart disease and type 2 diabetes mellitus, and her father had died of pelvic sarcoma.

On examination, there was generalised muscle wasting, particularly of the legs, and pseudoathetosis of the outstretched hands with eyes closed. She had impaired pinprick and light touch sensation throughout the left leg, from toe to knee on the right, and fingers to elbows in the upper limbs. Joint position was impaired up to the knees bilaterally. Her strength was mildly reduced bilaterally for hip flexion but otherwise surprisingly well preserved. Reflexes were all absent and the plantar responses were mute. Cranial nerve examination was normal.

She had a resting tachycardia and her systolic blood pressure fluctuated between 85 and 170 mm Hg. There were no palpable lymph nodes or organomegaly and breast examination was normal.

The patient's syndrome was a progressive, predominantly sensory impairment across all modalities, with largely …