Screening for osteoporosis: what is the role of heel ultrasound?

To the Editor: Vitamin BI2 deficiency is a well established cause of myelopathy and neuropathy. Further, chronic exposure to nitrous oxide (such as through recreational abuse) can lead to the same neurological syndromes in individuals who do not have vitamin BI2 deficiency. I This occurs because nitrous oxide causes irreversible oxidation of cobalt and active vitamin BI 2 requires cobalt in its reduced form. It is less well recognised that the same neurological syndromes may be precipitated after a single exposure to nitrous oxide anaesthesia in patients with subclinical vitamin BI 2 deficiency, as the following case illustrates. A 70-year-old woman was referred with painful paraesthesiae and difficulty walking. She had recently undergone a total abdominal hysterectomy and bilateral salpingooophorectomy for endometrial carcinoma. The anaesthetic lasted 105 minutes and there were no complications and, during that time, nitrous oxide was administered. She had an epidural infusion of pethidine for 68 hours after surgery. Her postoperative recovery was uneventful and she was discharged. Ten days after surgery she began to develop leg pains and "weakness", which progressed over the next four weeks to the point where she could not walk and had severe painful paraesthesiae, with "electricshock"-type pains when touched lightly on the legs. She was admitted to our unit, where she was found to have a severe sensory ataxia. Romberg's test was positive and there was pseudoathetosis of the fingers. Proprioception and vibration sense were severely impaired, especially in the lower limbs. Thermal and pinprick sensation were relatively spared. Muscle strength was only mildly impaired. Deep tendon reflexes were either severely depressed or absent; plantar reflexes were unreactive. Nerve conduction studies confirmed a neuropathy. Her haemoglobin concentration was 114 gIL (normal range, 120-155 gIL), with a mean cell volume of95fl (normal range, 8Q-95f1). Her vitamin B I 2 level was 35 pmol/L