Motor cortical dysfunction disclosed by single and double magnetic stimulation in patients with fibromyalgia

Objective: To investigate the motor cortex by single and double magnetic st imulation, in patients with fibromyalgia. Methods: Thirteen patients with fibromyalgia and 13 age-matched healthy sub jects were examined. We evaluated, in both limbs, motor evoked potential (M EP) latency and amplitude and the MCA/MPA ratio, i.e. MEP cortical amplitud e (MCA)/maximal peripheral amplitude of the M response (MPA), the central c onduction time (TCC) and the length of the silent period (SP). With double magnetic stimulation, different time intervals between shocks were used: wi th delays between shocks of 4, 25, 55 and 85 ms, the intensities of the con ditioning shock were 80% the relaxed threshold. With delays between shocks of 55, 85, 100, 155, 200, 255 and 355 ms, the intensities of the conditioni ng shocks were set at 150% the relaxed threshold. In all cases, the intensi ty of the test shock was 150% the relaxed threshold. The results were also compared with those obtained in 5 women affected by rheumatoid arthritis (R A). Results: As compared to control, the cortical relaxed threshold was enhance d on both sides and limbs (P < 0.05). The cortical silent period recorded w ith single magnetic stimulation was reduced in the upper limbs (P = 2.7 x 1 0(-11)) and lower limbs (both sides P = 3.6 x 10(-5). The other parameters investigated were normal. With double magnetic stimulation, facilitatory ph enomena were absent in fibromyalgic patients and the inhibitory responses r ecorded with a delay of 155 ms were reduced (P = 0.0052). No significant di fferences were noted between FM and RA patients. Conclusion: This study demonstrated motor cortical dysfunction in patients with fibromyalgia involving excitatory and inhibitory mechanisms. This indi cates motor cortical involvement and supports the hypothesis of aberrant ce ntral pain mechanisms. The absence of differences between FM and RA suggest that the lesions were not specific and could be related to chronic pain di sorders within the central nervous system. (C) 2000 Elsevier Science Irelan d Ltd. All rights reserved.