Following complete physical and neurologic examination, clinical pathologic evaluation can help identify possible metabolic causes of syncope or seizures. Cardiac troponin I is a myocardial-specific protein found in the contractile apparatus of the heart.11 Increased serum cardiac troponin I levels have been measured in humans with seizures and syncope and were found to be significantly more elevated in patients with syncope than in those with seizures; however, severe seizure disorders (eg, status epilepticus) can cause myocardial damage and may also result in elevated serum cardiac troponin I levels. In one veterinary study, serum cardiac troponin I levels were found to be significantly different between dogs with seizures and dogs with syncope11; however, notable overlap was found, thus rendering the test ineffective for definitively differentiating between the diseases in dogs. Troponin I levels do not reflect all causes of syncope.
Metabolic abnormalities associated with seizures, including hypoglycemia, hypocalcemia, elevated ammonia, and hypernatremia, can be readily identified on routine serum chemistry analysis. Evidence of these metabolic disorders concurrently identified in a patient with a history of acute loss of consciousness should lead to consideration for seizure disorder. Patients with metabolic disease can have concurrent cardiovascular disease; inclusion of other differentiating factors should be considered.
In human medicine, serum lactate levels measured within 2 hours of the episode of lost consciousness are significantly higher in patients with seizures compared with patients with syncope.10 This has yet to be verified in veterinary medicine but may become a readily available test to objectively differentiate between seizures and syncope in veterinary patients.