Evidence before this study
cluster headache, headache
ADVERSE EVENTS, CHRONIC CLUSTER HEADACHE, CLUSTER HEADACHE
We searched PubMed on November 13th, 2023, with the keywords “chronic cluster headache”, “cluster headache”, and “occipital nerve stimulation” (ONS), without restrictions to language or publication year. Of the 171 items, we excluded reviews and publications that did not report attack frequency at least 24 months after implantation. In publications combining different headache types, only data from patients with cluster headache were extracted. All publications only included data from retrospective or prospective long-term recordings of open-label assessment of the effect of ONS in case series. There were no prospective follow-up studies of the long-term effect of ONS in participants of a randomised controlled trial.We included 10 studies from 9 unique study populations of patients with medically intractable chronic cluster headache (MICCH) in this review. No formal meta-analysis was performed due to the large heterogeneity of the design, nature (retrospective versus prospective), outcome measures, follow-up time, inclusion criteria and results. Instead, balanced means and ranges across all studies are reported. In total, 293 unique participants are reported with a mean follow-up of 54 months (range 37–87).Most studies were small (<30 patients) and often there were methodological issues such as selection bias, uncertain length of the baseline period, incomplete or no formal statistical assessment at all of outcome and adverse events, little or no information on the number of participants that were lost to follow up and how these were statistically handled, and data reported only at the last follow-up with no information on effects at earlier intervals.All studies showed a reduction in attack frequency (mean 55%; median 50%, range 25%–95%). Detailed data on adverse events was lacking, but a mean of 58% (range 24%–80%) of participants experienced one or more (serious) adverse events during follow-up.