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Objective: To quantify temperature induced changes (=Uhthoff phenomenon) in ce ntral motor conduction and their relation to clinical motor deficits in 20 multi ple sclerosis (MS) patients. Methods: Self assessment of vulnerability to tempe rature and clinical examination were performed. We used motor evoked potentials to measure central motor conduction time (CMCT) and applied the triple stimulat ion technique (TST) to assess conduction failure. The TST allows an accurate qua ntification of the proportion of conducting central motor neurons, expressed by the TST amplitude ratio (TST AR). Results: Temperature induced changes of TST AR were significantly more marked in patients with prolonged CMCT (P=0.037). The re was a significant linear correlation between changes of TST AR and walking v elocity (P=0.0002). Relationships were found between pronounced subjective vulne rability to temperature and (i) abnormal CMCT (P=0.02), (ii) temperature induced changes in TST AR (P=0.04) and (iii) temperature induced changes in walking ve locity (P=0.04). CMCT remained virtually unchanged by temperature modification. Conclusions: Uhthoff phenomena in the motor system are due to varying degrees of conduction block and associated with prolonged CMCT. In contrast to conduction block, CMCT is not importantly affected by temperature. Significance: This is th e first study quantifying the Uhthoff phenomenon in the pyramidal tract of MS pa tients. The results suggest that patients with central conduction slowing are pa rticularly vulnerable to develop temperature dependent central motor conduction blocks.
Objective: To quantify temperature induced changes (= Uhthoff phenomenon) in central motor conduction and their relation to clinical motor deficits in 20 multi ple sclerosis (MS) patients. Methods: Self assessment of vulnerability to tempe rature and clinical examination were performed. We used motor evoked potentials to measure central motor conduction time (CMCT) and applied the triple stimulation technique (TST) to assess conduction failure. The TST allows an accurate qua ntification of the proportion of conducting central motor neurons, expressed by the TST amplitude ratio (TST AR). Results: Temperature induced changes of TST AR were significantly more marked in patients with prolonged CMCT (P = 0.037). The re was a significant linear correlation between changes of TST AR and walking v elocity (P = 0.0002). Relationships were found between pronounced subjective vulne rability to temperature and (i) abnormal CMCT (P = 0.02), (ii) temperature induced changes in TST AR (P = 0.04) and Conclusions: Uhthoff phenomena in the motor system are due to varying degrees of conduction block and associated with prolonged CMCT. In contrast to the conduction block, CMCT is not importantly affected by temperature. Significance: This is th e first study quantifying the Uhthoff phenomenon in the pyramidal tract of MS pa tients. The results suggest that patients with central conduction slowing are pa rticularly vulnerable to develop temperature dependent central motor conduction blocks.