Migraine affects approximately 15% of the global population. Its prevalence doubles or even triples in individuals with chronic inflammatory conditions, such as chronic inflammatory rheumatic diseases (34%), multiple sclerosis (MS) (46%), or endometriosis (35%). The prevalence of chronic migraine - defined as at least 15 headache days per month (on average over the past 3 months), of which at least 8 days have migrainous features - is also higher in certain conditions such as MS (4%) compared to the general population (1%). The mechanisms underlying migraine and its chronification remain uncertain, but inflammation appears to play an important role in its pathophysiology: it is present from the onset of a migraine attack, represented by the release of pro-inflammatory cytokines that sensitize the trigeminal system and promote the occurrence of new attacks. The investigators' recent bibliographic work has demonstrated elevated levels of interleukin-6 (IL-6), a pro-inflammatory cytokine, in the blood of episodic migraine patients between attacks (migrainous status) compared to non-migrainous subjects, and in chronic migraine patients compared to episodic migraine patients (chronic migraine status). IL-6 appears to play a role in the pathophysiology of migraine, and elevated levels may represent a marker of poorer response to prophylactic treatments. IL-6 levels are also elevated in inflammatory rheumatic diseases and are associated with disease severity. The efficacy of IL-6 pathway-blocking treatments in inflammatory rheumatic diseases is now well established, and these agents are commonly used for this indication. IL-6 could therefore represent a shared pathophysiological link between migraine and inflammatory rheumatic diseases. However, no study to date has measured the effect of IL-6-blocking treatments on migraine. This study therefore aims to assess the effect of anti-IL-6 treatments on migraine in migrainous patients followed in the rheumatology department of the Clermont-Ferrand University Hospital and treated with anti-IL-6 therapy for their rheumatological condition (rheumatoid arthritis, polymyalgia rheumatica, etc.). It will provide preliminary results regarding the effect of anti-IL-6 agents on migraine and could justify future therapeutic studies.

In this study, the investigators aim to measure the proportion of patients experiencing a reduction in migraine among those treated with anti-IL-6 therapy for their rheumatological condition, in terms of migraine frequency or intensity (primary objective). The secondary objectives are to :

• Measure the proportion of patients experiencing a reduction in migraine among those treated with anti-IL-6 therapy for their rheumatological condition, in terms of (a) frequency, (b) intensity, (c) both frequency and intensity of migraines.
• Compare the proportion of patients experiencing a reduction in migraine in terms of frequency or intensity between those treated with anti-IL-6 and a group of patients treated with anti-TNF (tumor necrosis factor) therapy.

From a pre-established list compiled by the investigators of patients on anti-IL-6 therapy (anti-IL-6 group) and patients on anti-TNF therapy (control group), all patients will be contacted by phone to identify those with migraine, using the International Classification of Headache Disorders, version 3 (ICHD-3) criteria from the International Headache Society (IHS). In cases where migraine is present, the effect of anti-IL-6 (anti-IL-6 group) or anti-TNF (control group) treatment in terms of the proportion of patients experiencing a reduction in migraine will be assessed using the Patient Global Impression of Change (PGI-C) score: a validated tool, widely used, translated into French and made available by eProvide - Mapi Research Trust [https://eprovide.mapi-trust.org/instruments/patient-global-impressions-scale-change-improvement-severity#need\_this\_questionnaire\]) (comparison: before vs. during treatment). The episodic or chronic nature of migraine will be determined during the telephone interview according to the following criteria: fewer than 15 monthly headache days for episodic migraine, and at least 15 monthly headache days - of which at least 8 days have migrainous features - for chronic migraine (IHS definition). All patients on this list who meet the inclusion and non-inclusion criteria and agree to participate in the study will be enrolled. The inclusion of a control group - comprising patients treated with a biotherapy other than anti-IL-6, namely anti-TNF agents - will strengthen the level of attribution of the measured effect to anti-IL-6 treatment and help offset recall bias.

Inclusion Criteria (for screening) :

• at least 18 years old
• ongoing or previous anti-IL-6 (anti-IL-6 group) or anti-TNF (anti-TNF group) therapy, taken for at least 3 months

Inclusion Criteria (patients to be enrolled) : migrainous patients, identified using the International Classification of Headache Disorders, version 3 (ICHD-3) criteria from the International Headache Society (IHS) during the telephone call

Exclusion Criteria:

• Biotherapy treatment in the context of a diagnosis of giant cell arteritis
• Verbal communication not possible
• No affiliation to the French national health insurance system, legal protection measure (guardianship, curatorship, judicial protection)

Migrainous patients, identified using the International Classification of Headache Disorders, version 3 (ICHD-3) criteria from the International Headache Society (IHS) during the telephone call, will complete the Patient Global Impression of Change (PGI-C) score to determine whether the treatment (anti-IL-6 or anti-TNF) is associated with a reduction in migraines or not.