F-wave characteristics as surrogate markers of spasticity in patients with secondary progressive multiple sclerosis.

We sought to identify significant ulnar nerve conduction abnormalities and also to detect ulnar F-wave variable changes in patients with secondary progressive multiple sclerosis (MS). Conventional conduction study was performed unilaterally to ulnar nerves of eight men and 12 women with secondary progressive MS (mean age, 47.5 +/- 6.6 years), having spastic hemiparesis and hand spasticity. A series of 40 electrical stimuli were also delivered to their ulnar nerves unilaterally so as to obtain F waves. The side of examination was ipsilateral to the side of spastic paresis. The following F-wave variables were estimated: F-wave persistence, latency, amplitude, duration, and F chronodispersion. Ten patients with remitting-relapsing MS without any evidence of hand spasticity and 20 age- and gender-matched healthy volunteers served as controls. Motor and sensory conduction study was normal in all participants. The F-wave persistence, latency, and duration parameters and also the F chronodispersion were comparable between groups. The mean and maximum F-wave amplitude values (P = 0.005) and the F mean/M (P = 0.001) and F maximal/M (P = 0.001) ratios were significantly higher than those of controls. Finally, the F-wave amplitude parameters in patients with secondary progressive MS significantly correlated with the degree of spasticity and the duration of disease. Significant amplitude F-wave abnormalities occurred in patients with secondary progressive MS and hand spasticity, emphasizing the contribution of upper motor neurons damage in the genesis of F waves.