Transient loss of consciousness (LOC) is very common issue. Syncopes and generalized tonicclonic
(GTC) seizures are common causes mostly differentiated by history. Several laboratories
serum markers (mostly creatine kinase and lactate) can be helpful especially when history is
unreliable. We explore the potential supporting role of electrolytes plasma level in that
setting.
We retrospectively collected 178 consecutive episodes of loss of consciousness in adults from
the EEG database of our hospital (CHUV, Lausanne) seen over 3 years in our emergency
department. Plasma level of the different electrolytes (sodium, potassium, phosphate,
calcium, magnesium) were recorded as well as basic demographics, diagnosis, blood sample
delay and history of alcohol abuse.
We analysed 128 episodes with sufficient documentations (7 had uncertain diagnosis): we
compared electrolytes values between GTC seizures (75 episodes) and other LOC, (46
episodes). Phosphate and calcium levels were associated with GTC seizures; median=0.79
(range 0.34-1.37) vs 0.93 mmol/l (range 0.52-1.56) p=0.001 for phosphate and median= 2.32
(range 1.92-2.53) vs 2.27 mmol/l (range 2.0-2.53) p=0.03 for calcium. Considering abnormal
values, only hypophosphatemia (94% of abnormal phosphate level) was associated with GTC
seizures with 37 (51 %) abnormal phosphate in GTC seizures and 15 (33%) in other LOC
(p=0.02, Chi squared), independently from blood sampling delay, alcohol abuse and other
electrolytes level. Hypophosphatemia below 0.6 mmol/L was 93% sensitive and 85% specific
of GTC seizure. Hypophosphatemia was self-limited.
Our data suggest that transient hypophosphatemia is common after GTC seizures. This
hypophosphatemia is unlikely to be causing the seizure, but is rather a consequent
intracellular shift. Phosphate level could be another biological marker helping differentiate
GTC seizures from other LOC, especially when history is unclear. Timing of the blood sample
should be taking into account in its interpretation. A prospective study is needed to confirm
these findings.