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Abstract Background Although acute headache following COVID-19 vaccination is widely acknowledged, the long-term progression of these headaches remains poorly understood. Our objective was to identify various phenotypes of prolonged or worsened headaches associated with COVID-19 vaccination and document any changes in these phenotypes over an extended period. Additionally, we aimed to document the diverse headache presentations among patients with pre-existing primary headaches. Methods A multinational, prospective observational study was conducted to investigate prolonged or worsened headaches associated with COVID-19 vaccination. Questionnaires assessing COVID-19 vaccination-related headaches at three time points (initial visit, 3rd month follow-up, and 6th month follow-up) were developed for the study. Headache specialists/clinicians evaluated patients using these questionnaires in a prospective manner. Repeated K-means cluster analysis was performed to identify patient profiles with prolonged or worsened headaches related to COVID-19 vaccination. Results Among the 174 patients included in the study, there was a female-to-male ratio of 128 (73.6%) to 46 (26.4%). The mean age of the patient group was 45.2 ± 13.3 years, and 107 patients (61.5%) had a pre-existing history of primary headaches. Through the analysis, two major clusters were identified based on headache characteristics at each visit. During the first visit (n = 174), Cluster 1 primarily comprised patients with a history of primary headaches, frontal localization of pain, throbbing pain type, more severe headaches accompanied by symptoms such as nausea, phonophobia, photophobia, and osmophobia, and worsened by physical activity. In contrast, Cluster 2 consisted of patients with longer headache durations (over one month) and a stabbing/pressing quality of pain. Patients in Cluster 1 had a higher prevalence of migraine as the pre-existing primary headache disorder compared to Cluster 2 (90.48% vs. 68.18%, respectively; p = 0.005). Conclusion The identification of two distinct phenotypes of prolonged or worsened headaches related to COVID-19 vaccination can provide valuable clinical insights. Having an awareness of the potential worsening of headaches following COVID-19 vaccination, particularly in patients with a primary headache disorder such as migraine, can help clinicians and headache experts anticipate and adjust their treatment strategies accordingly. This knowledge can aid in preplanning treatment modifications and optimize patient care.

ObjectiveTo investigate the possible subgroups of patients with Cluster Headache (CH) by using K-means cluster analysis.MethodsA total of 209 individuals (mean (SD) age: 39.8 (11.3) years), diagnosed with CH by headache experts, participated in this cross-sectional multi-center study. All patients completed a semi-structured survey either face to face, preferably, or through phone interviews with a physician. The survey was composed of questions that addressed sociodemographic characteristics as well as detailed clinical features and treatment experiences.ResultsCluster analysis revealed two subgroups. Cluster one patients (n = 81) had younger age at diagnosis (31.04 (9.68) vs. 35.05 (11.02) years; p = 0.009), a higher number of autonomic symptoms (3.28 (1.16) vs. 1.99(0.95); p < 0.001), and showed a better response to triptans (50.00% vs. 28.00; p < 0.001) during attacks, compared with the cluster two subgroup (n = 122). Cluster two patients had higher rates of current smoking (76.0 vs. 33.0%; p=0.002), higher rates of smoking at diagnosis (78.0 vs. 32.0%; p=0.006), higher rates of parental smoking/tobacco exposure during childhood (72.0 vs. 33.0%; p = 0.010), longer duration of attacks with (44.21 (34.44) min. vs. 34.51 (24.97) min; p=0.005) and without (97.50 (63.58) min. vs. (83.95 (49.07) min; p = 0.035) treatment and higher rates of emergency department visits in the last year (81.0 vs. 26.0%; p< 0.001).ConclusionsCluster one and cluster two patients had different phenotypic features, possibly indicating different underlying genetic mechanisms. The cluster 1 phenotype may suggest a genetic or biology-based etiology, whereas the cluster two phenotype may be related to epigenetic mechanisms. Toxic exposure to cigarettes, either personally or secondarily, seems to be an important factor in the cluster two subgroup, inducing drug resistance and longer attacks. We need more studies to elaborate the causal relationship and the missing links of neurobiological pathways of cigarette smoking regarding the identified distinct phenotypic classes of patients with CH.