OBJECTIVES: Use functional brain imaging to explore activity changes in centres involved in trigeminal pain processing and control before and after occipital neurostimulation in drug-resistant chronic cluster headache patients.BACKGROUND: Occipital nerve stimulation (ONS) provides relief to about 60% of patients suffering from drug-resistant chronic cluster headache (drCCH). Its mode of action, however, remains elusive, but the long latency to meaningful effect suggests that ONS induces slow neuromodulation.METHODS: Ten drCCH patients underwent an 18FDG-PET scan after ONS durations varying between 0 and 30 months. All were scanned with ongoing ONS (ON) and with the stimulator switched OFF.RESULTS: After 6-30 months of ONS, 3 patients were pain free and 4 had a ≥ 90% reduction of attack frequency (responders). In patients overall compared to controls, several areas of the pain matrix were hypermetabolic: ipsilateral hypothalamus, midbrain and ipsilateral lower pons. All normalized after ONS, except the hypothalamus. Switching ON or OFF the stimulator had little influence on brain glucose metabolism. The perigenual anterior cingulate cortex (PACC) was hyperactive in ONS responders compared to non-responders.INTERPRETATION AND CONCLUSIONS: Metabolic normalization in the pain neuromatrix and lack of short-term changes induced by the stimulation support the hypothesis that ONS acts in drCCH through slow neuromodulatory processes. Selective activation in responders of PACC, a pivotal structure in the endogenous opioid system, suggests that ONS may restore balance within dysfunctioning pain control centres. That ONS is nothing but a symptomatic treatment might be illustrated by the persistent hypothalamic hypermetabolism which could explain why autonomic attacks may persist despite pain relief and why cluster attacks recur shortly after stimulator arrest.
