OBJECTIVE: To test the hypothesis that patients with rheumatoid arthritis (RA) 
have clinical or subclinical evidence of peripheral neuropathy or myopathy.
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 electromyographic 
examination of 4 muscles [extensor digitorum communis (EDC), biceps brachii 
(BB), vastus lateralis (VL), and tibialis anterior (TA)] on the right side in 
both groups. Quantitative data included percentage of polyphasic potentials, 
motor unit potential amplitude, area, duration, turns, and number of polyphasic 
potentials.
RESULTS: There were statistically significantly higher proportions of polyphasic 
potentials in 3 muscles in patients compared with controls. Mean number of 
phases in EDC was 4.6 (SD 0.4) in the patients and 4.1 (0.5) in controls (p = 
0.0001). The values for the VL were 4.1 (SD 0.4) in patients compared with 3.6 
(0.4) in controls (p = 0.0001), and in the TA 4.5 (SD 0.5) versus 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 motor 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.