We describe a case of bilateral weakness of the lower limbs, sensory disturbance and intermittent urinary incontinence, secondary to untreated Gitelman’s syndrome, in a 42-year-old female who was referred with presumed cauda equina syndrome. On examination, the power of both legs was uniformly reduced, and the perianal and lower-limb sensation was altered. However, MRI of the lumbar spine was normal. Measurements of serum and urinary potassium were low and blood gas analysis revealed metabolic alkalosis. Her symptoms resolved following potassium replacement.

We emphasise the importance of measurement of the plasma and urinary levels of electrolytes in the investigation of patients with paralysis of the lower limbs and suggest that they, together with blood gas analysis, allow the exclusion of unusual causes of muscle weakness resulting from metabolic disorders such as metabolic alkalosis.