Nociceptive threshold in patients with epilepsy

Clinical practitioners have often observed in the course of their daily work that the pain thresholds of epileptic patients seem to differ from those of healthy subjects. These patients can suffer from quite severe traumatic lesions without apparently experiencing any pain. Since they are usually under treatment for epilepsy, it is difficult to determine whether the absence of pain is due to these patients' epileptic condition or to its treatment, since most antiepileptic drugs also have analgesic effects. In the present study, it was proposed to assess the pain thresholds of 15 epileptic patients (10 with tonic-clonic seizures generalized at outset and 5 with temporal lobe epilepsy), by measuring the leg flexion nociceptive reflex (or RIII reflex) threshold: the stimulation threshold at which this reflex is triggered is known to be correlated with the pain threshold. The nociceptive threshold of the patients with generalized epilepsy was not found to differ from that of the control population, whereas that of the patients with temporal lobe epilepsy was spontaneously high and was not reversed upon injecting naloxone. These data are discussed from the point of view of the pain pathways and mechanisms possibly involved.