[Determination of the latency for the prognosis of Bell's palsy (author's transl)].

In a previous study the authors discussed the value of the determination of the compound action potential amplitude of the m. orbicularis oris following supramaximal stimuli of the facial nerve for the prognosis of facial paresis. In this study they investigate the suitability of the determination of the latency periods for an early prognosis. The latency periods in 20 normal subjects and 26 patients with idiopathic facial paresis were messured and continuously checked. The study reveals that a difference of more than 0.5 msec. between the latency periods of normal and paretic patients does not even permit the proof of peripheral lesions in patients with partial denervation or absent or insufficient recovery. Ocassionally, even shorter latency were observed in paretic patients, which are probably due to a local increase of the threshold for supramaximal stimuli around the stimulation electrode. The necessary increase of the stimulus intensity probably leads to a nervous excitation further distally. Contrary to the observations of other authors these studies indicate that the determination of the latency does not constitute a useful prognostic criterion for idiopathic facial paresis; for an early prognosis the measurement of latency is less reliable than the determination of the compound action potential amplitude.