Strength-duration time constant in peripheral nerve: no abnormality in multiple sclerosis

Objectives. To investigate the properties of the strength-duration time constant (SDTC) in multiple sclerosis (MS) patients. Methods. The SDTC and rheobase in 16 MS patients and 19 healthy controls were obtained following stimulation of the right median nerve at the wrist. Results. SDTC and rheobase values were 408.3 ± 60.0 μs and 4.0 ± 1.8 mA in MS patients, versus 408.0 ± 62.4 μs and 3.8 ± 2.1 mA in controls. The differences were not significant in SDTC or rheobase values between the patients and controls (P = 0.988 for SDTC and P = 0.722 for rheobase). Conclusion. Our study showed no abnormality in relapsing remitting MS patients in terms of SDTC, which gives some indirect information about peripheral Na(+) channel function. This may indicate that alterations in the Na(+) channel pattern in central nervous system (CNS) couldnot be shown in the peripheral nervous system (PNS) in the MS patients by SDTC. The opinion that MS can be a kind of channelopathy might be proven by performing other axonal excitability tests or SDTC in progressive forms of MS.