Hypophosphatemia as Potential Biomarker of Tonic-Clonic Seizures in the Emergency Room

Transient alteration of consciousness is common in the emergency department. Tonic-clonic seizures (TCS) are a frequent presumptive diagnosis, but there is no reliable postictal biological marker. We report the case of a 19-year-old man with two episodes of generalized TCS, four months apart. Both were associated with moderate-to-severe hypophosphatemia (0.9 mg/dL, reference range 3.0-4.5 mg/dL). The investigation of phospho-calcium metabolism was negative, and phosphorus levels normalized between the two episodes and after the second TCS. The diagnosis of epilepsy was made based on the occurrence of two unprovoked TCS 24 hours apart. The patient started antiseizure medication after the second TCS and has remained free of seizures (20 months of follow-up). Routine EEG with sleep showed slow temporal activity without epileptiform activity, and the brain magnetic resonance imaging was normal. Changes in serum phosphorus are not usually associated with acute symptomatic seizures. In this case, hypophosphatemia might have been a marker of TC.