Number of patient-reported allergies helps distinguish epilepsy from psychogenic nonepileptic seizures

Psychogenic nonepileptic seizures (PNES) are relatively common, accounting for 5-40% of visits to tertiary epilepsy centers. Inpatient video-electroencephalogram (vEEG) monitoring is the gold standard for diagnosis, but additional positive predictive tools are necessary given vEEG's relatively scarce availability. In this study, we investigated if the number of patient-reported allergies distinguishes between PNES and epilepsy. Excessive allergy-reporting, like PNES, may reflect somatization. Using electronic medical records, ICD-9 codes, and text-identification algorithms to search EEG reports, we identified 905 cases of confirmed PNES and 5187 controls with epilepsy but no PNES. Patients with PNES averaged more self-reported allergies than patients with epilepsy alone (1.93 vs. 1.00, p<0.001). Compared to those with no allergies, each additional allergy linearly increased the percentage of patients with PNES by 2.98% (R(2)=0.71) such that with ≥12 allergies, 12/28 patients (42.8%) had PNES compared to 349/3368 (11.6%) of the population with no allergies (odds ratio=6.49). This relationship remained unchanged with logistic regression analysis. We conclude that long allergy lists may help identify patients with PNES. We hypothesize that a tendency to inaccurately self-report allergies reflects a maladaptive externalization of psychologic distress and that a similar mechanism may be responsible for PNES in some patients with somatic symptom disorder.