Long-term effectiveness and safety of occipital nerve stimulation in medically intractable chronic cluster headache: a prospective follow-up study of the randomised controlled ICON trial.

Abstract text (incl. figure legends and references)

Question: We have shown in the ICON study that occipital nerve stimulation (ONS) is safe and effective in medically intractable chronic cluster headache (MICCH). This prospective follow-up evaluates the long-term effectiveness and safety.

Methods: Every six months, participants completed questionnaires on the attack-frequency, adverse events, subjective improvement and willingness to recommend this treatment to other patients. Missing values for log-transformed attack-frequency were imputed for up to 5 years of follow-up. Descriptive analyses are presented as (pooled) geometric or arithmetic means and 95% confidence intervals.

Results: Of the n=119 eligible participants, n=88 (74%) provided informed consent and were followed ≥2 years unless the device was prematurely removed. There were n=73 (83%) active participants after 2 years, n=60 (68%) after 3 years, n=32 (36%) after 5 years and n=3 (3%) after 8.5 years. Mean follow-up was 4.2 ± 2.2 years for a total of 370 person-years. Of the 49/88 (56%) ≥50% responders at the end of the ICON study, 35/49 (71%) retained this response and 15/39 (38%) of the non-responders became a ≥50% responder for at least half the follow-up period. The pooled geometric mean [95% CI] weekly attack frequency remained considerably lower after one (4,2; 2,8 - 6,3), two (5,1; 3,5 - 7,6) and five years (4,1; 3,0 - 5,5) compared to baseline (16,2; 14,4 - 18,3). Most participants (69/88; 78%) reported a subjective improvement from baseline at the last follow-up and 70/88 (81%) would recommend this treatment to other patients. Additional surgery was required in 112/122 (92%) hardware related events in 44/88 participants (50%), corresponding to a hardware-related additional surgery rate of 0.35 person-year-1 [0.28 – 0.41]. No predictive factors for effectiveness at 2 years after the ICON study, i.e. 3 years after ONS implantation were observed.

Conclusions: ONS is a safe, well-tolerated and long-term effective treatment for MICCH.