Isolated lower motoneuron involvement following radiotherapy.

tunnel syndrome: electrophysiological study.cies through the tarsal tunnel in normal adult subjects: standard determinations corrected for temperature and distance. Arch Phys Med Rehab 1980;61:243-8. 4Dekel S, Coates R. Primary carpal stenosis as a cause of "idiopathic" carpal tunnel syndrome. Alteration of the visual blink reflex in patients with dementia Sir: The clinical diagnosis of senile dementia of the Alzheimer type and multi-infarct de-mentia can be very difficult.' 2 Neu-rophysiological tests are not specific. In a recent study, the EEG and visual evoked potentials were reported to be normal in respectively 34% and 76% of patients with Alzheimer type dementia.3 Therefore, the development of additional sensitive tests which could discriminate dementia from other disorders, would be of great value. We have found a simple neurophysio-logical test, the visual blink reflex, to be abnormal in patients with Alzheimer type dementia or multi-infarct dementia. The visual blink reflex consists of a reflex contraction of the eyelids in response to a bright light which is flashed in front of the eyes of the subject. Normal subjects usually show a visual blink reflex with a constant latency of approximately 50 ms, although the visual blink reflex can be absent in up to 12% of normals.4 The visual blink reflex is a subcor-tical reflex but the exact pathway in the brainstem is unknown.5 6 Fifteen patients with senile dementia (Alzheimer type dementia or multi-infarct dementia) (mean age 77 2 + 7.7 yr) were examined according to the method described by Malin.4 The EMG activity of the or-bicularis oculi muscles was recorded with surface skin electrodes. Patients were not informed that the blink reflex was measured in order to avoid voluntary blinking. In each subject we determined the average latency time of the visual blink reflex from 10 trials. The controls were 13 normal aged persons (mean age 70 5 + 11 yr). Letters Twelve out of 15 patients showed a symmetrical visual blink reflex with a mean latency for the group of 1043 + 300ms (range 65-158 ms). In three patients no visual blink reflex could be elicited. The visual blink reflex of the group of normal subjects had a mean latency of 49 7 + 2 2 ms (range 47-533 ims). The visual blink reflex was absent in one control. The mean laten-cies of the patient and the control group differed significantly (p < 0 001). Our study demonstrates that the latency of the visual …