Acute hypomagnesaemia causing intra-operative lower limb movements in a paraplegic patient, despite full neuromuscular blockade

Alterations in electrolyte homeostasis associated with major surgery, intravenous fluid therapy, malnutrition, and critical illness are common but usually non-specific. This case report describes the sudden onset of forceful rhythmic flexion movements in both lower limbs during scoliosis surgery in a 12-year-old paraplegic boy with spina bifida. These movements arose despite adequate depth of anaesthesia, complete neuromuscular blockade, and treatment of hypocalcaemia. They persisted post-operatively after reversal of neuromuscular blockade and emergence from anaesthesia. Hypomagnesaemia was identified and treated post-operatively which coincided with cessation of the movements. We deduce hypomagnesaemia to be the aetiology of this unusual clinical presentation. This report underscores the interdependency of Ca2+ and Mg2+ homeostasis in excitable tissues and emphasizes that abnormalities observed in each cation should not be considered independently. In the perioperative care of spinal fusion patients, hypocalcaemia is a well-recognised and understood complication.