Reduced alpha-band phase coherence and cortical complexity in fibromyalgia: A tms-eeg exploratory study

Cortico-spinal excitability of the primary motor cortex (M1) is reduced in fibromyalgia, and repetitive transcranial magnetic stimulation (TMS) targeting M1 normalizes these changes and relieves symptoms. TMS combined with electroencephalography (TMS-EEG) allows the measurement of M1 excitability and its connectivity to other regions, which may help clarify neurophysiological abnormalities in fibromyalgia. We assessed cortical excitability, oscillatory activity, and complexity in individuals with fibromyalgia compared to pain-free healthy controls.

Global- and local-mean field power, peak-to-peak amplitude, event-related spectral perturbation, intertrial coherence (ITC), natural frequency, and perturbational complexity index (PCIst) of the EEG response after left-M1 TMS were compared between groups (n = 18 fibromyalgia; n = 15 controls). Pain intensity, interference, current therapy, mood, and quality of life were assessed in individuals with fibromyalgia.

Compared with controls, individuals with fibromyalgia showed a reduction in the alpha-band ITC in middle- (p = 0.044) and right-parieto-occipital areas (p = 0.040). Middle-parieto-occipital ITC negatively correlated with reported pain relief (rho = -0.552, p = 0.019). The PCIst was lower in fibromyalgia compared with controls (p = 0.009) and correlated with higher pain interference in general activity (rho = -0.486, p = 0.042).

Individuals with fibromyalgia have abnormal cortical connectivity compared with asymptomatic controls.

TMS-EEG may provide insights on brain connectivity relevant for prognostication and therapy in fibromyalgia.