The Diagnostic Utility of Hypophosphatemia for Differentiation of Generalized Tonic-Clonic Seizures from Syncope in Dogs: A Case-Control Study
Introduction
In human patients, transient hypophosphatemia is commonly detected after generalized tonic-clonic seizures (GTCS), and serum phosphorus concentration (sPi) is a useful marker to differentiate GTCS from other causes of transient loss of conciseness (TLOC), namely syncope, especially when the episode was unwitnessed. The aim of this retrospective study was to examine the occurrence of hypophosphatemia in dogs presented to an emergency service due to seizures compared to those presented due to syncope, and assess the usefulness of hypophosphatemia as a diagnostic marker for canine GTCS.
Methods
Computerized medical records were searched (January 2018–August 2021) for the terms “seizure”, “epilepsy”, “status epilepticus” and “syncope”. Dogs were included if the episode occurred ≤3 from presentation, and if sPi and serum creatinine (sCr) were measured. Dogs were excluded if aged <1-year or if sCr exceeded 2 mg/dL.
Results
The study included 87 and 26 dogs diagnosed with seizures or syncope, respectively. There were no group differences in serum concentrations of creatinine, sodium, chloride, potassium or glucose. Hypophosphatemia (sPi <3 mg/dL, RI 3–6.2 mg/dL) occurred in 28 dogs (32%) in the seizure group, of which nine (10%) had sPi <2 mg/dL. In the syncope group, no dog had sPi levels below 3 mg/dL. Median sPi was significantly (P=0.00003) lower in the seizure group (3.1 mg/dL; range, 0.93–6.77) compared to the syncope group (4.2 mg/dL; range, 3–8.4). Furthermore, in dogs that presented while seizing (24/87; 28%) median sPi was significantly lower (P=0.05) compared to those that were not (2.8 mg/dL; range, 0.93–5.39 vs. 3.2; range, 1.03–6.77). ROC analysis of sPi as a marker for GTCS yielded an area under the curve of 0.757 (95% confidence interval 0.667–0.847), with an optimum cutoff point of 3.0 md/dL, corresponding to specificity and sensitivity levels of 100% and 44%, respectively.
Conclusion
Based on these results, sPi following TLOC might serve as a diagnostic tool to differentiate GTCS from syncope in dogs. Hypophosphatemia, especially with sPi concentration <3 mg/dL, in samples collected ≤3 hours post-TLOC may be useful in clinical practice to rule in a GTCS episode.
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