gms | German Medical Science

Objective: The neurophysiological assessment of syringomyelia has been unsatisfactory. Crossing spinothalamic fibers that convey pain and sensation are anatomically placed at highest risk of being compromised in the early stage of syringomyelia. The testing of silent periods (SP) hase been proven to be sensitive for detecting alterations in this pathway.

Methods: 37 patients with syringomyelia were included in the study: Routine electrophysiological measurements were applied including SEP and MEP recordings for all extremities. SP were recorded from the pollicis brevis muscle and electrical stimuli were applied to the ipsilateral digiti II. 20 healthy controls were recorded to set up a baseline value. Sensitivity and specificity values were statistically evaluated according to the main clinical symptoms (hypaesthesia, paresis, dissociative syndrome and pain). The study was approved by the local ethic committee.

Results: All control patients showed normal silent periods in the voluntarily activated pollicis brevis muscle. In syringomyelia patients, the affected limb demonstrates pathological silent periods for all syndrome qualities (Sensitivity 30-50%), whereas pain was the most specific (90%), despite normal values in SEP and MEP recordings. Non-expansive hereditary hydromyelia does not alter the silent periods, whereas small syringes show pathological values.

Conclusions: Upper extremity silent period testing is a sensitive neurophysiological technique and an invaluable tool for preoperative assessment of syringomyelia. These silent periods are highly associated with early dysfunction of thin myelinated spinothalamic tract fibers, when routine electrophysiological measurements still show normal values. Conduction abnormalities that selectively abolish the silent periods can distinguish between a physiologic hydromyelia and space-occupying syringomyelia.