Somatosensible evoked potentials following stimulation of the trigeminal nerve in diagnostics of brainstem lesions

Somatosensible evoked potentials (SEP) following stimulation of the trigemi nal nerve provide additional diagnostic information in brainstem lesions. A fter stimulation of the upper and lower lip (separately or simultaneously) the afferent impulses reach the Nd. sensorius principalis nervi trigemini i n the pens via the Gasseri ganglion. From there the impulses ore transmitte d by the lemniscus trigeminalis to the thalamus and terminate in the postce ntral gyrus (area 3b). The latency of the P19-peak is the most important pa rameter. Separate stimulation of the upper and lower lip allows for detecti on of even discrete lesions in the trigerminal system. By combining trigemi nal SEP with other techniques such as auditory evoked potentials or blink r eflex the exact localisation of brainstem lesions may be identified. Trigem inal SEP show in 41-100% of multiple sclerosis patients additional, clinica lly inapparent, foci. Also in ischemic brainstem lesions trigeminal SEP may provide additional information. In trigeminal neuralgia as well as in neur inoma of the acoustical nerve affection of the brainstem may be recognised by trigeminal SEP.