Background: Refractory chronic migraine affects approximately 4% of the population worldwide and results in severe pain, lifestyle limitations, and decreased quality of life. Occipital nerve stimulation (ONS) refers to the electric stimulation of the distal branches of greater and lesser occipital nerves; the surgical technique has previously been described and has demonstrated efficacy in the treatment of a wide variety of headache disorders.
Objectives: The aim of this study is to evaluate the long-term efficacy and tolerability of ONS for medically intractable chronic migraine.
Study design: Prospective, long-term, open-label, uncontrolled observational study.
Setting: Single public university hospital.
Methods: Patients who met the International Headache Society criteria for chronic migraine, all of them having been previously treated with other therapeutic alternatives, and who met all inclusion and exclusion criteria for neurostimulation, received the implantation of an ONS system after a positive psychological evaluation and a positive response to a preliminary occipital nerve blockage. The implantation was performed in 2 phases: a 10 day trial with implanted occipital leads connected to an external stimulator and, if more than 50% pain relief was obtained, permanent pulse generator implantation and connection to the previously implanted leads. After the surgery, the patients were thoroughly evaluated annually using different scales: pain Visual Analogue Scale (VAS), number of migraine attacks per month, sleep quality, functionality in social and labor activities, reduction in pain medication, patient satisfaction, tolerability, and reasons for termination. The average follow-up time was 9.4 ± 6.1 years, and 31 patients completed a 7-year follow-up period.
Results: Thirty-seven patients were enrolled and classified according to the location and quality of their pain, accompanying symptoms, work status, and psychological effects. Substantial pain reduction was obtained in most patients, and the VAS decreased by 4.9 ± 2.0 points. These results remained stable over the follow-up period. Five of the 35 permanently implanted patients with migraine attacks at baseline were free from these attacks at their last visits, whereas the pain severity decreased 3.8 ± 2.5 (according to the VAS) in the remaining patients. Seven of the 35 permanent implanted devices were definitively removed: 2 devices because of treatment inefficacy, and 5 devices because the patients were asymptomatic and considered to be cured from their pain, even with the stimulation off. Systemic side effects were not observed.
Limitations: Limitations of the current study include its uncontrolled and open-label design. Additionally, not all patients completed the 7-year follow-up period.
Conclusions: We consider that the trigemino-cervical autonomous and cervical connection may explain why ONS might relieve chronic migraine pain, but this is just a theoretical explanation which should be demonstrated in future studies. The results achieved in this study suggest that ONS may provide long-term benefits for patients with medically intractable chronic migraine. These outcomes are slightly better than previous reports and were maintained over the 7-year follow-up. We believe that an accurate selection of patients, realization of diagnostic occipital nerve blocks, psychological evaluations, rigorous surgical technique, and appropriate parameter programming helped us achieve these outcomes. Key words: Refractory chronic migraine, headache, occipital nerve stimulatino, peripheral nerve stimulation, occipital nerve block.