Clinical utility of serum lactate levels for differential diagnosis of generalized tonic-clonic seizures from psychogenic nonepileptic seizures and syncope

- The differential diagnosis of generalized tonic clonic seizures, psychogenic nonepileptic seizures and syncope constitutes a major challenge
- Both PNES and syncope may appear identical to true epileptic seizures and lead to incorrect diagnosis
- Serum lactate can provide useful information when incorporated into the appropriate clinical context

BackgroundThe differential diagnosis of generalized tonic-clonic seizures (GTCS), psychogenic nonepileptic seizures (PNES), and syncope constitutes a major challenge. Misdiagnosis rates up to 20 to 30% are reported in the literature.PurposeTo assess the clinical utility of serum lactate levels for differentiation of GTCS, PNES, and syncope based on gender differences.MethodsData from 270 patients were evaluated retrospectively. Only patients ≥ 18 years old with the final diagnosis of GTCS, PNES, or syncope in their chart were recruited. Serum lactate levels were measured in the first 2 h of the index event.ResultsSerum lactate levels in patients with GTCS (n = 157) were significantly higher than in the patients with PNES (n = 25) (p < 0.001) and syncope (n = 88) (p < 0.001). When compared with the females, serum lactate levels in patients with GTCS were significantly higher in the male subgroup (p = 0.004). In male patients the ROC analysis yielded a serum lactate value of 2.43 mmol/l with a sensitivity of 0.85 and a specificity of 0.88 as the optimal cut-off value to distinguish GTCS from other events. The ROC analysis for the AUC yielded a high estimate of 0.94 (95% confidence interval: 0.91-0.98). When a cut-off value of 2.43 mmol/l was chosen for the females, which was an optimal value for male patients, the specificity was 0.85, however, the sensitivity was 0.64.ConclusionWe propose that serum lactate level when measured in the first 2h after the index event has a high clinical utility in the differential diagnosis of GTCS, PNES, and syncope. With concomitant clinical signs and physical examination findings besides neuroimaging and EEG, elevated levels of lactate should be taken into account when evaluating a patient with impaired consciousness. On the other hand, the suggested cut-off value 2.43 mmol/l might not have a discriminative effect between GTCS, PNES, and syncope in female patients. This finding should be verified in a prospectively designed study with a larger patient population.