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 stimulation, in patients with fibromyalgia. Methods: Thirteen patients with fibromyalgia and 13 age-matched healthy subjects were examined. We evaluated, in both limbs, motor evoked potential (MEP) latency and amplitude and the MCA/MPA ratio, i.e. MEP cortical amplitude (MCA) /maximal peripheral amplitude of the M response (MPA), the central conduction time (TCC) and the length of the silent period (SP). With double magnetic stimulation, different time intervals between shocks were used: with delays between shocks of 4, 25, 55 and 85 ms, the intensities of the conditioning shock were 80% the relaxed threshold. With delays between shocks of 55, 85, 100, 155, 200, 255 and 355 ms, the intensities of the conditioning shocks were set at 150% the relaxed threshold. In all cases, the intensity of the test shock was 150% the relaxed threshold. The results were also compared with those obtained in 5 women affected by rheumatoid arthritis (RA). Results: As compared to control, the cortical relaxed threshold was enhanced on both sides and limbs (P<0.05). The cortical silent period recorded with single magnetic stimulation was reduced in the upper limbs (P=2.7×10−11) and lower limbs (both sides P=3.6×10−5). The other parameters investigated were normal. With double magnetic stimulation, facilitatory phenomena were absent in fibromyalgic patients and the inhibitory responses recorded with a delay of 155 ms were reduced (P=0.0052). No significant differences were noted between FM and RA patients. Conclusion: This study demonstrated motor cortical dysfunction in patients with fibromyalgia involving excitatory and inhibitory mechanisms. This indicates motor cortical involvement and supports the hypothesis of aberrant central pain mechanisms. The absence of differences between FM and RA suggest that the lesions were not specific and could be related to chronic pain disorders within the central nervous system.