Reduced plasma calcitonin gene-related peptide level identified in cluster headache: A prospective and controlled study.

Background: The role of calcitonin gene-related peptide (CGRP) in the cyclic pattern of cluster headache is unclear. To acquire biological insight and to comprehend why only episodic cluster headache responds to CGRP monoclonal antibodies, we examined whether plasma CGRP changes between disease states (i.e. bout, remission and chronic) and controls.
Methods: The present study is a prospective case-control study. Participants with episodic cluster headache were sampled twice (bout and remission). Participants with chronic cluster headache and controls were sampled once. CGRP concentrations were measured in plasma with a validated radioimmunoassay.
Results: Plasma was collected from 201 participants diagnosed with cluster headache according to the International Classification of Headache Disorders, 3rd edition, and from 100 age- and sex-matched controls. Overall, plasma CGRP levels were significantly lower in participants with cluster headache compared to controls ( p  < 0.05). In episodic cluster headache, CGRP levels were higher in bout than in remission (mean difference: 17.1 pmol/L, 95% confidence interval = 9.8-24.3, p  < 0.0001). CGRP levels in bout were not different from chronic cluster headache ( p  = 0.266).
Conclusions: Plasma CGRP is unsuitable as a diagnostic biomarker of cluster headache or its disease states. The identified reduced CGRP levels suggest that CGRPs role in cluster headache is highly complex and future investigations are needed into the modulation of CGRP and its receptors.
Competing Interests: Declaration of conflicting interestsASP reports being a sub-investigator in trials and received a restricted research grant from Lundbeck (payed to the institution), which manufactures Eptinezumab, a monoclonal antibody targeting CGRP under investigation as a preventive treatment for cluster headache. KM reports no disclosures. SLC reports no disclosures. MB reports no disclosures. NRJ reports no disclosures. LK reports no disclosures. RHJ reports lectures for Eli-Lilly, which manufactures Galcanezumab, a monoclonal antibody targeting CGRP and FDA approved as a preventive treatment for episodic cluster headache. RHJ also reports lectures, acting as an investigator in clinical trials and receiving funding in the form of a restricted and an unrestricted research grant (paid to the institution) from Lundbeck, which manufactures Eptinezumab, a monoclonal antibody targeting CGRP under investigation as a preventive treatment for cluster headache.