A man presenting with limb weakness and electrolyte imbalance

A 39-year-old man presented with lower limb muscle pains and weakness which had progressed rapidly over the preceding 2 weeks. Immediately prior to hospital admission he was unable to stand unaided. There had been no disturbance of bulbar, sensory or sphincter function and he reported no recent gastrointestinal symptoms. Medical history included colitis, which was quiescent. His only regular medication was olsalazine. On examination, he was normotensive (and remained so throughout his admission). There was no rash. Cardiovascular, respiratory and abdominal examinations were normal. Neurological examination revealed generalised weakness in all four limbs, most marked proximally. Tendon reflexes were preserved. Plantar response was flexor. Examination of cranial nerves was normal. Laboratory investigations revealed a serum potassium of 1.8 mmol/l. Serum sodium, urea and creatinine were within normal limits. Creatine kinase was 10 719 IU/l. A quadriceps muscle biopsy was performed and the histology is shown in figure 1. Further investigations included an abdominal ultrasound scan, following which computed tomography (CT) of the abdomen was performed (figure 2). A 24-hour urine collection for catecholamines was undertaken (table). View this table: Table Levels of free …