Myopathy and neuropathy in rheumatoid arthritis. A quantitative controlledelectromyographic study

Objective. To test the hypothesis that patients with rheumatoid arthritis ( RA) have clinical or subclinical evidence of peripheral neuropathy or myopa thy. Methods, We studied 40 seropositive women with RA, mean age 46.6 years (SD 6.4), and 56 healthy controls, mean age 43.0 years (SD 9,1), Patients had a mean disease duration of 13.0 years (SD 7.8). We performed electromyograph ic examination of 4 muscles [extensor digitorum communis (EDC), biceps brac hii (BB), vastus lateralis (VL), and tibialis anterior (TA)] on the right s ide in both groups. Quantitative data included percentage of polyphasic pot entials, motor unit potential amplitude, area, duration, turns, and number of polyphasic potentials, Results. There were statistically significantly higher proportions of polyp hasic potentials in 3 muscles in patients compared with controls. Mean numb er of phases in EDC was 4.6 (SD 0.4) in the patients and 4.1 (0.5) in contr ols (p = 0.0001). The values for the VL were 4.1 (SD 0.4) in patients compa red with 3.6 (0.4) in controls (p = 0.0001), and in the TA 4.5 (SD 0.5) ver sus 4.0 (0.4) (P = 0.0001). We also found significantly increased duration of motor unit potentials in the VL and TA of patients. The amplitudes of mo tor unit action potentials were not significantly different in the 2 groups . Conclusion. The study reveals an increased prevalence of neurogenic but not myogenic changes in patients with RA compared with controls.