Autonomic dysfunction during the interictal period: an electrophysiologic study

Objective: Autonomic nervous system dysfunction during the interictal period of epileptic seizures is still poorly understood. We assessed sympathetic and parasympathetic functions during the interictal period using sympathetic skin response (SSR) and R-R interval variability (RR-IV) methods in patients with epilepsy. Methods: We questioned the presence of autonomic symptoms in 50 patients with epilepsy and 42 healthy controls. We also measured SSR and RR-IV percentage (RR-IV%) at rest, deep inspiration, and during the Valsalva maneuver. Orthostatic hypotension (OH) was also evaluated. Results: Of the 50 patients with epilepsy, 21 patients had temporal lobe epilepsy (TLE) and 29 had extratemporal lobe epilepsy. Autonomic symptoms (orthostatic intolerance, gastromotor, pupillomotor, vasomotor, secretomotor symptoms) and OH were significantly more common in patients with TLE (p<0.05). The SSR amplitude was higher in patients than in controls (p<0.05) and the RR-IV% values at rest, during deep inspiration, and during the Valsalva maneuver were significantly lower in the patient group than in the control group (p<0.01 for each). As a result, autonomic symptoms were more common in patients with TLE comparing with extratemporal epilepsy in the interictal period. RR-IV% values were lower than in the control group at rest, deep inspiration, and the Valsalva maneuver in patients with epilepsy. Sympathetic skin response amplitude is higher in patients with generalized seizures, reflecting increased sympathetic responsiveness in the interictal period. Conclusion: Our study demonstrated clinical and electrophysiologic findings supporting autonomic system dysfunction in patients with epilepsy during the interictal period.