Hypophosphatemia compared to classical biomarkers of tonic clonic seizures

Hypophosphatemia was recently reported as a potential marker of tonic-clonic (TC) seizures among patients with transitory loss of consciousness (TLOC). Its value compared to classical markers (creatine kinase [CK] and lactate) is however unknown.

Compare the diagnostic performance of hypophosphatemia, plasma CK, and lactate levels for distinguishing TC seizures from other TLOCs, alone or in combination.

128 patients aged 18-90, consecutively admitted to our hospital emergency department for TLOC were included. Diagnostic accuracy of plasma phosphate, CK, and lactate levels were compared with ROC curves.

We found significantly higher CK (median 154 U/l, range 38-5608; vs 115.5, 37-2340 U/l; p = 0.037) and lower phosphatemia (median 0.79 mmol/l, 0.34-1.37; vs 0.93, 0.52-1.89 mmol/l, p = 0.007) in TC seizures compared to other TLOCs; lactatemia was not different, although using a smaller sample (n = 72). Hypophosphatemia was the only independent predictor of TC seizures, even in later samples (>2 h). Comparing ROC curves, Combining hypophosphatemia and hyperCKemia had higher diagnostic accuracy for TC seizures than hyper-CKemia alone (AUC 0.68, 95 % CI 0.571-0.783 vs. 0.59, 95 % CI 0.475-0.706; p = 0.018), but the combination was only marginally better than hypophosphatemia alone (AUC 0.67, 95 % CI 0.559-0.778).

Hypophosphatemia seems to be more useful than CK levels for diagnosing TC seizures in patients assessed in an emergency setting for TLOC. Combining both parameters together does not significantly increase the diagnostic yield. No conclusion could be drawn regarding the comparison with lactate. A prospective study is needed.