Decline of muscle fiber conduction velocity during short-term high-dose methylprednisolone therapy.

The influence of five days' high-dose methylprednisolone therapy (2500 mg cumulative dose) on muscle fiber conduction velocity (MFCV) and muscle force was investigated in a group of patients without primary muscle involvement (MS-patients during a relapse). A significant decrease in MFCV was found. The decrease in MFCV was associated with a non-significant increase of the force of the investigated muscle. The general muscle force increased significantly. This increase seems related to the beneficial effect of the therapy on the central nervous system dysfunction. It is suggested that the decrease of MFCV is caused by a partial, corticosteroid-induced, depolarization of the muscle fiber membrane. Since the scatter of MFCVs increases, it is likely that not all fibers are equally sensitive to the changes in membrane properties.