A potential role of hypophosphatemia for diagnosing convulsive seizures: A case-control study.

Transient loss of consciousness (TLOC) is a common presentation in the emergency room, where patient history can usually differentiate syncope from generalized tonic-clonic (GTC) seizures. Several serum markers, such as creatine kinase and lactate, can be helpful, especially when history is unreliable. Here, we explore a potential supporting role of electrolyte plasma levels in a case-control study.In our electroencephalographic database, we retrospectively identified consecutive episodes of loss of consciousness in adults seen over 3 years in our hospital emergency department for a case-control study. We investigated plasma levels of several electrolytes (sodium, potassium, phosphate, calcium, magnesium) at the emergency visit, as well as demographics, diagnosis, blood-sample delay time, and history of alcohol abuse.

Of the 126 patients identified, 75 had GTC seizures and 46 had other TLOC causes. Among electrolyte levels, only hypophosphatemia was associated with GTC seizures (median = 0.79 mmol·L^-1 , range = 0.34-1.37 in GTC seizures vs 0.93 mmol·L^-1 , range = 0.52-1.56, P = 0.001 in TLOC). After adjusting for blood sampling delay, alcohol abuse, and other electrolyte levels, only hypophosphatemia was associated with GTC seizures, occurring in 37 (51%) of GTC seizures and 12 (22%) of other TLOC (odds ratio = 3.5, 95% confidence interval = 1.5-8.3, P = 0.003). Hypophosphatemia < 0.6 mmol·L^-1 was 93% specific and 20% sensitive for GTC seizure occurrence. In follow-ups, hypophosphatemia was transitory.

Transient hypophosphatemia is common after GTC seizures and could represent an additional biological marker to help differentiate GTC seizures from other TLOC, especially when history is unclear. This hypothesis needs to be tested prospectively.