Inhibitory Effects of Steroid-Induced Myopathy on Muscle Fiber Conduction Velocity
Muscle fiber conduction velocity (MFCV) has been reported to decrease in patients with myopathy. However, there has been no rerport regarding changes in MFCV in steroid-induced myopathy (SM). In this study, MFCV in rats with SM was compared with that in normal rats and a new technique for measuring MFCV in a single motor unit was established using the multi-point stimulation (MPS) technique. Ten eight-week-old male Wistar rats were treated with intramuscular injections of triamcinolone acetonide for two weeks (SM group). Ten eight-week-old normal male rats were reared for two weeks as the control group. After the right sciatic nerve and soleus muscle were exposed, an original four-channel surface electrode array was placed over the muscle belly parallel to the fibers. Several sites of the sciatic nerve were stimulated electrically using the MPS technique. MFCV was calculated from the distance of each electrode and each time lag between neighboring potentials. Twenty MFCV values of different motor units per each material were measured, and the values were averaged. There were significant differences in the mean MFCV values between the SM group and the control group. The number of MFCV values greater than 4.0 m/sec significantly decreased in the SM group, while the lowest values were the same as those in the normal group. The mean MFCV value in the SM rats decreased significantly compared to that in the normal rats. The decrease in the fast values of MFCV was in excellent agreement with the atrophy of type 2A fibers with a fast MFCV component in the SMrats.