Table 3 Eligibility criteria

Inclusion criteria

• Age of 18 years and above

• Signed informed written consent

• Chronic cluster headache with ≥ 15 attacks per month

• Stable use of preventive cluster headache medication 30 days prior to study enrollment

Exclusion criteria

• Other ongoing neuromodulation therapies

• Current alcohol and/or drug abuse

• Known severe psychiatric disorders

• A concomitant second type of chronic primary or chronic secondary headache (e.g., chronic migraine or chronic post-traumatic headache, while chronic tension-type headache is allowed)

• Major posterior cervical surgery at C3-level and above

• Pregnancy

• Treatment with oral steroids and/or GON block 30 days before study enrollment