1. Centre for Cluster Headache, Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
2. Department of Clinical Neuroscience, Karolinska Institutet, 171 76 Stockholm, Sweden
3. Department of Neurology, Danderyd Hospital, 182 88 Stockholm, Sweden
4. Department of Neurology, Karolinska University Hospital, 171 64 Stockholm, Sweden