Objectives: Motor cortex disinhibition has a role in the mechanism of neuropathic pain. The duration of the cortical silent period (CSP) is used as a measure of excitability in cortical inhibitory circuits. We investigated cortical disinhibition in diabetic patients with and without neuropathic pain.
Materials and methods: We studied diabetic patients with (n = 20) and without (n = 50) neuropathic pain, and control subjects (n = 30). Transcranial magnetic stimulation (TMS) was performed on the right hemisphere at rest, and surface electromyography was recorded from the left first dorsal interosseous muscle for evaluation of motor evoked potential (MEP) latency and amplitude. CSP was recorded from the left FDI, and TMS was then delivered while the subject was performing a voluntary contraction.
Results: We showed a low resting motor threshold, a short CSP duration, and a low CSP duration/MEP amplitude ratio in patients with neuropathic pain (P < 0.0001, P < 0.0001, P < 0.0001).
Conclusions: Our findings demonstrate that diabetic patients with neuropathic pain have a cortical disinhibition.