Untangling the mess of CGRP levels as a migraine biomarker: an in-depth literature review and analysis of our experimental experience.

BACKGROUND: Calcitonin gene-related peptide (CGRP) is the most promising candidate to become the first migraine biomarker. However, literature shows clashing results and suggests a methodological source for such discrepancies. We aimed to investigate some of these methodological factors to evaluate the actual role of CGRP as biomarker. METHODS: Previous to the experimental part, we performed a literature review of articles measuring CGRP in migraine patients. Using our 399 bio-bank sera samples, we performed a series of experiments to test the validity of different ELISA kits employed, time of sample processing, long-term storage, sampling in rest or after moderate exercise. Analysis of in-house data was performed to analyse average levels of the peptide and the effect of sex and age. RESULTS: Literature review shows the high variability in terms of study design, determination methods, results and conclusions obtained by studies including CGRP determinations in migraine patients. CGRP measurements depends on the method and specific kit employed, also on the isoform detected, showing completely different ranges of concentrations. Alpha-CGRP and beta-CGRP had median with IQR levels of 37.5 (28.2-54.4) and 4.6 (2.4-6.4)pg/mL, respectively. CGRP content is preserved in serum within the 24 first hours when samples are stored at 4°C after clotting and immediate centrifugation. Storages at -80°C of more than 6 months result in a decrease in CGRP levels. Moderate exercise prior to blood extraction does not modulate the concentration of the peptide. Age positively correlates with beta-CGRP content and men have higher alpha-CGRP levels than women. CONCLUSIONS: We present valuable information for CGRP measurements in serum. ELISA kit suitability should be tested prior to the experiments. Alpha and beta-CGRP levels should be analysed separately as they can show different behaviours even within the same condition. Samples can be processed in a 24-h window if they have been kept in 4°C and should not be stored for more than 6 months at -80°C before assayed. Patients do not need to rest before the blood extraction unless they have performed a high-endurance exercise. For comparative studies, sex and age should be accounted for as these parameters can impact CGRP concentrations.

Increased prevalence of migraine in women with inflammatory bowel disease: A cross-sectional study.

BACKGROUND: Some studies have suggested an association between migraine and inflammatory bowel disease. We determined migraine prevalence in a cohort of patients with inflammatory bowel disease. METHODS: Patients with inflammatory bowel disease aged 18-65 years were interviewed using an ad hoc headache questionnaire. Those who admitted a history of headache in the last year answered the three questions of the ID-Migraine questionnaire. Those who answered "yes" to the three of them were classified as "definite" and those who answered "yes" to two were classified as "probable" migraine. RESULTS: We interviewed 283 patients with inflammatory bowel disease. Of these, 176 (62.2%) had headache. Fifty-nine (20.8%; 95% CI 16.3-26.0%) met migraine criteria either definite (n = 33; 11.7%; 95% CI 8.2-16.0%) or probable (n = 26; 9.2%; 95% CI 6.1-13.2). When divided by gender, 12 men (9.6%; 95% CI 5.1-16.2%) and 47 women (29.8%; 95% CI 22.8-37.5%) met migraine criteria. The prevalence of migraine was increased in inflammatory bowel disease patients from the current cohort (20.8%) versus that reported for our general population for the same age group (12.6%; p < 0.0001). These differences remained significant in female inflammatory bowel disease patients (29.8% versus 17.2% in our general population; p < 0.0001), but not in males (9.6% in inflammatory bowel disease vs 8.0%; p = 0.30). Seventeen patients with inflammatory bowel disease (6.0%; 95% CI 3.54-9.44%) fulfilled chronic migraine criteria. There were no differences in migraine prevalence by inflammatory bowel disease subtypes. CONCLUSION: Migraine prevalence, including chronic migraine, seems to be increased in patients with inflammatory bowel disease. The fact that this association was stronger for women suggests an influence of sex-related factors.