Action of dantrolene sodium in spasticity with low dependence on fusimotor drive.

The effects of dantrolene sodium, an anti-spasticity drug with a site of action within the muscle fibres, were studied in 19 patients with spastic paresis. Oral doses were successively increased from 100 mg/day to a maximal tolerated level or up to 800 mg/day. Trial periods were 8-13 weeks. The responses of stretch reflexes to local cooling over the spastic muscles were used to differentiate alpha and gamma spasticity. In the knee extensor and flexor muscle groups, cryo-negative alpha-spasticity was seen in 25 and cryo-positive gamma-spasticity in 4 muscle groups. Ankle clonus was cryo-positive in 14 of 15 cases. Resistance to passive knee joint movements, ankle clonus and isometric or isokinetic muscle strength was determined quantitatively. The gait was recorded by intermittent-light photography and the muscle activation patterns in gait were studied in recordings of the average EMG from limb muscles. Functional disability and spasms were assessed from clinical examinations and interviews. Passive resistance at slow (6%/sec) and fast (30 degrees/sec) knee joint movements decreased by 32% in the extensor muscles (p = 0.005 resp. 0.001) and by 23-26% in the flexor muscles (not significant). Reduced passive resistance was observed in 16 of the muscles with alpha-spasticity and in all 4 of the muscle groups with gamma-spasticity. Clonus was diminished or abolished in 14 of 15 patients with this sign. Maximal isometric or isokinetic muscle strength was unaltered in the majority of the patients. In a few the strength was increased, in some it was decreased. The averaged EMG activity during walking as studied in 10 patients were increased in 35 of the 57 muscle groups examined. In some muscle groups, exaggerated activity attributable to spastic reflexes was reduced. Motor disability was decreased significantly in 10 patients. It was not significantly changed in 5 and deteriorated in 4 patients. Drowsiness and subjective muscle weakness were the most frequent side-effects. SGOT and SGPT were increased in 3 cases.