Brainstem Reflexes and Trigeminal Evoked
Potentials after Electrical Stimulation In patients reporting pain in the trigeminal territory, neurophysiological testing of trigeminal function offers the clinician useful information. An objective demonstration of dysfunction is provided in all patients with pain secondary to a documented disease such as symptomatic trigeminal neuralgia (TN), postherpetic neuralgia, vascular malformations, benign tumors of the cerebellopontine angle and multiple sclerosis, even in those patients who have no clinical signs or complaints other than pain. [1][2][3] Brainstem reflexes are more extensively and markedly affected in patients with constant pain than in those with paroxysmal pain. This finding agrees with the common notion that a dysfunction of few fibers provokes paroxysmal pain, whereas severe damage does not. In symptomatic trigeminal pains, the trigeminal reflexes yield a very high sensitivity, probably because they allow examination of all three divisions. The most sensitive reflexes are the R1 blink reflex and the SP1 masseter inhibitory period. [1][2][3] Although, like others, we have occasionally seen patients with mild reflex abnormalities, in the majority of patients with idiopathic TN (tic douloureux), all reflexes are normal. 1-3 A diagnostic protocol for patients with trigeminal pain should rely primarily on brainstem reflexes; the technique is easier and less invasive than that for evoked potentials, and the finding of any abnormality suggests an underlying structural lesion. In patients with paroxysmal pain, the presynaptic waves of the scalpevoked potential after infraorbital stimulation are more sensitive, possibly because a slight slowing of conduc-