Migraine is not associated with enhanced atherosclerosis

Study population

We performed a case-control study nested within the population-based ERF study. The ERF study is a family-based cross-sectional study in a genetically isolated community in the Southwest of the Netherlands (14). The study population includes 3465 individuals who were ascertained for genetic-epidemiological studies based on their genealogical background (i.e. not selected on phenotypes of interest). All individuals 18 years or older were invited to participate. For this epidemiological study we did not use genetic or genealogical data, but the genetic and environmental homogeneity of the population can be an advantage. The study was approved by the Medical Ethical Committee of the Erasmus Medical Centre Rotterdam and all participants gave written informed consent.

Migraine patients and controls

Migraineurs were identified using a three-stage screening procedure assessing lifetime occurrence of migraine, which was previously validated in a population-based study (15) and which was based on the second edition of the International Classification of Headache Disorders (ICHD-II) (1). The sensitivity of this case-finding procedure was 0.93 and the specificity was 0.36. The positive predictive value was 0.65 and the negative predictive value was 0.91. Thus the screening procedure picked up many false-positives and missed some true-positives (15). Only patients with “definite” MA and MO are included. Patients with probable migraine are excluded from the study.

Details on the migraine case-finding procedure have been published before (16). In brief, in the first stage, participants were asked to fill out five screening questions on headache and aura symptoms. Then, screen-positives received a detailed questionnaire on headache and aura symptoms. Finally, screen-positives were interviewed by telephone for further clarification of their answers. Subjects who were screen-positive but did not return the extensive headache questionnaire and subjects who could not be screened because they did not (completely) fill out the screening questions were directly contacted by telephone. Telephone interviews were performed by the principal study physician (A.H.S.), who is experienced in diagnosing migraine patients, and by well-trained medical students supervised by A.H.S. A final diagnosis was made only after the telephone interview and in consultation with a neurologist specializing in headache (G.M.T.).

The control group consisted of subjects who 1) did not report severe headache in their lifetime (only headache up to pain severity score ≤4 on a scale from 0 to 10); 2) did not report visual aura symptoms; 3) had never been diagnosed with migraine by a physician; and 4) never used specific antimigraine medication. Thus, subjects with mild headache in combination with visual aura are excluded from the control group. To exclude false-negative control cases, we used an even more conservative definition for non-migraineurs than in our previous population-based study, as from this study we know that about 10% of migraineurs are missed using this screening procedure (15).

Assessment of cardiovascular parameters

Participants (n = 3465) were asked to attend the research center located within the community. Extensive clinical examinations were performed, including the collection of fasting blood samples, anthropometric measurements, cardiovascular assessments, and personal interviews by physicians. Participants were also asked to fill out questionnaires assessing various variables, including symptoms of headache and their level of education. The interview included questions on cigarette smoking status, alcohol consumption, and medical history. Alcohol consumption was measured in units per week and was categorized as <28 consumptions per week and ≥28 consumptions per week. Current smoking was categorized as yes or no. Participants took all prescription medication to the research center, and antihypertensive treatment and the use of oral contraceptives (OAC) was verified by a physician. Height and weight were measured with the participant in light underclothing and body mass index (kg/m²) was computed. An ECG was performed, and each was scored by an experienced cardiologist. Blood pressure was measured twice on the right arm in a sitting position after at least 5 minutes of rest using an automated device (OMRON 711, Automatic IS; Vernon Hills, IL, USA). The average of the two measures was used for the brachial blood pressure in the analyses. Plasma concentrations of triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC) were determined according to standard procedures, as described previously (14). Diabetes was defined as the use of blood glucose-lowering medication or sober glucose levels of ≥7 mmol/l or both. Total plasma adiponectin was analyzed with the Human Adiponectin radioimmunoassay (RIA) kit (catalog number: HADP-61HK) of Linco Research (St. Charles, MO, USA). Total plasma C-reactive protein (CRP) was analyzed with the US C-reactive protein enzyme-linked immunosorbent assay (ELISA) (catalog number: DSL-10-42100) of Diagnostic Systems Laboratories Inc. (Webster, TX, USA). All measurements were performed according to the manufacturers’ protocol. Plasma CRP levels showed a high level of kurtosis. Therefore, upper plasma CRP levels exceeding three times the standard deviation of the mean were removed from further analyses.

We used the FRS-CHD (17) and FRS-Stroke (18) to summarize the data. The FRS-CHD estimates the 10-year probability of CHD, defined as myocardial infarction or CHD death. The score assigns points for age, HDL-C, TC, smoking status, and systolic blood pressure stratified by sex and treatment for hypertension. The FRS-Stroke estimates the 10-year probability of stroke. The score assigns points for age, systolic blood pressure, treatment for hypertension, history of diabetes mellitus, smoking status, cardiovascular disease (i.e. history of myocardial infarction, angina pectoris, coronary insufficiency, intermittent claudication or congestive heart failure), and atrial fibrillation and left ventricular hypertrophy on ECG, all stratified by sex. The individual points for both the FRS-CHD and FRS-Stroke scores are summed and converted into 10-year risk percentages.

Functional and structural vascular assessment

The atherosclerotic process can be assessed by means of non-invasive preclinical functional and structural markers of changes in the vessel wall, including intima media thickness (IMT), pulse wave velocity (PWV, measure of arterial stiffness), and ankle-brachial index (ABI) (13). These measures correlate with central (IMT, PWV) or peripheral (ABI) atherosclerosis (13). IMT was measured by ultrasonography with a 7.5-MHz linear array transducer (ATL Ultra-Mark IV; Advanced Technological Laboratories, Bothell, WA, USA) of the left and right common carotid artery. The maximum carotid IMT was determined as the mean of the maximum IMT of near and far wall of both common carotid arteries (14). Carotid-femoral PWV was measured by means of an automatic Complior SP device with subjects in the supine position. The time delay between the rapid upstroke from the base point of simultaneously recorded pulse wave curves in the carotid and the femoral arteries was assessed, and the distance between the carotid and the femoral arteries was measured over the surface of the body with a tape measure. PWV was calculated as the ratio between the distance traveled by the pulse wave and the time delay and expressed in meters per second (14). Ankle blood pressure was measured in both the posterior tibial arteries by using an 8-MHz continuous Doppler probe. Blood pressure was measured twice in the right arm in the sitting position. The ABI was calculated for each leg by dividing the ankle systolic pressure by the mean brachial systolic pressure. The lowest of the two ABI values was used in the analysis. Patients with ABI >1.4 were excluded from the analysis as this indicates non-compressible vessels (19).

Statistical methods

Analyses were performed separately for all migraine, MO and MA. A two-sided p value of alpha <0.05 was considered significant. General characteristics were compared between groups using a Student’s t test for age and a Chi-square test for sex and education. Means for continuous variables and proportions for dichotomous variables were calculated for cardiovascular risk parameters. Means of cardiovascular parameters were compared according to migraine status using analyses of covariance, adjusted for age, sex and education. Mean PWV, IMT and ABI were corrected for age, sex, education, HDL-C and smoking. Proportions were compared by binary logistic regression with the risk factor as the outcome (dependent) variable and migraine status as the independent variable, adjusted for age, sex and education. Odds ratios for having an FRS-CHD or FRS-Stroke >10% were calculated using logistic regression adjusted for age, sex and education. We had 80% power to detect a difference of 0.23 m/s for PWV, 0.03 mm for IMT and 0.016 for ABI. These power calculations are based on the number of participants with data available for that parameter.

Analyses were performed using SPSS version 16.0 (SPSS, Chicago, IL, USA). Significant results were corrected for inbreeding using the SOLAR 2.1.2 software package (Southwest Foundation for Biomedical Research, San Antonio, TX, USA), which is necessary because subjects are part of a genetic isolate. The absolute numbers of cases and controls with diabetes was too small to correct for inbreeding. The coefficient of inbreeding per individual was calculated based on available genealogical information using PEDIG software. The inbreeding coefficient indicates, for each person in ERF, the probability that two alleles at a given locus in an individual are identical by descent and thus is a measure for relatedness. Subjects of the ERF population are the living descendants of 22 couples with at least six children baptized in the community church between 1850 and 1900. Thus, they are part of a large extended pedigree and therefore are more related than individuals from the general population. In isolated populations such as ERF, genetic drift may lead to an increased risk of allele frequencies, which may (falsely) increase associations between traits. Correction for relatedness prevents this and better reflects the association in the general population.

Recruitment of migraine cases and controls

Results on ascertainment of migraine cases and controls have been described elsewhere and are depicted in the flowchart (Figure 1) (18). In total, 3465 subjects participated in the study, from whom we recruited 360 migraine patients (151 MA, 209 MO) and 617 control subjects. Comparing subjects included (n = 977) versus those not included (n = 2488) in the present study showed that included subjects were significantly younger (p < 0.001) and higher educated (p = 0.03) compared with those not included, but there was no difference with regard to gender (p = 0.20). OPEN IN VIEWER

Cardiovascular parameters

Baseline characteristics are shown in Table 1. In line with the higher prevalence of migraine in women, more women were present in the migraine group. Migraineurs, in particular MA, had lower levels of education. Smoking was more prevalent in migraineurs, in particular in MA (49% versus 31% of controls, p < 0.001). MA patients had a modestly decreased HDL-C (uncorrected difference 0.05 mmol/l, p < 0.001). After correction for menopause status, alcohol consumption and smoking status, which are known to influence HDL-cholesterol levels, the difference between MA patients and controls remained significant. Migraine patients were more likely to have diabetes (5.4% MA, 5.5% MO versus 3.2% controls, p < 0.05). The mean 10-year probability of CHD (FRS-CHD) or stroke (FRS-Stroke) was similar in migraine patients and controls (Table 1). None of the odds ratios for having a 10-year risk for FRS-Stroke or FRS-CHD larger than 10% reached statistical significance (data not shown).

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Table 1.

Baseline characteristics of the study population by migraine subtype.

	All migraine	p value	MO	MA	p value	Controls
	n = 360		n = 209	n = 151		n = 617
Age, year	46.2 (12.3)	0.149	47.0 (12.7)	45.1 (11.6)	0.105	47.8 (15.3)
% Female	75%	<0.001	77%	73%	MA: <0.001 MO: <0.001	47%
Education, %
Higher	5	0.02	5	4	MA: 0.04 MO: 0.10	9
Medium	64		63	66		65
Lower	31		32	30		26
Body mass index, kg/m2	27.1 (5.1)	0.10	27.2 (5.3)	26.9 (4.9)	0.24	26.8 (4.5)
SBP, mm Hg	135.3 (18.2)	0.22	135.4 (18.6)	135.2 (17.6)	0.42	139.4 (19.5)
DBP, mm Hg	79.2 (9.2)	0.13	79.3 (9.5)	79.0 (8.8)	0.33	79.7 (9.8)
LDL-C, mmol/l	3.75 (0.97)	0.10	3.73 (1.01)	3.78 (0.93)	0.19	3.66 (0.94)
HDL-C, mmol/l	1.30 (0.35)	0.02	1.35 (0.36)	1.23 (0.34)	MA: <0.001 MO: 0.53	1.28 (0.34)
Triglycerides, mmol/l	1.27 (0.67)	0.36	1.25 (0.66)	1.31 (0.69)	0.46	1.31 (0.77)
Total cholesterol, mmol/l	5.6 (1.1)	0.32	5.6 (1.1)	5.6 (1.0)	0.60	5.5 (1.0)
Diabetes, %	5.5	0.01	5.5	5.4	MA: 0.02 MO: 0.04	3.2
Current smoking, %	45	0.005	41	49	MA: <0.001 MO: 0.11	31
Alcohol consumption, u/w	5.4 (7.8)	0.06	5.0 (7.8)	5.8 (7.8)	0.15	8.2 (10.4)
CRP, mg/l	5.3 (4.3)	0.24	5.0 (4.1)	5.6 (4.4)	0.23	5.4 (4.5)
Adiponectin, mmol/l	11.1 (6.0)	0.58	11.3 (6.0)	10.8 (6.1)	0.69	10.2 (5.2)
FRS-Stroke, %	5.7 (0.3)	0.55	5.8 (0.4)	5.6 (0.3)	0.80	5.9 (0.2)
FRS-Stroke >10 % (% of subjects)	12		14	10		15
FRS-CHD, %	5.0 (0.2)	0.82	5.0 (0.4)	5.0 (0.3)	0.97	5.1 (0.2)
FRS-CHD >10 % (% of subjects)	12		12	11		22

Functional and structural measures for atherosclerosis

ABI data were available for 408 control subjects, 179 MO patients and 140 MA patients, IMT data for 470 control subjects, 167 MO patients and 123 MA patients, PWV data for 542 control subjects, 185 MO patients and 133 MA patients. Baseline characteristics including a predicted 10-year FRS-Stroke and FRS-CHD were not significantly different between the subjects with and without missing data. No difference was observed in mean IMT, carotid-femoral PWV, or ABI between migraineurs and controls (Table 2). All values observed for these three measurements were within the normal range (13).

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Table 2.

Functional and structural measures of atherosclerosis in migraine patients versus controls.

	All migraine	MO	MA	Controls	p value
Common carotid IMT, mm	0.77 (0.16)	0.77 (0.17)	0.77 (0.14)	0.79 (0.20)	0.55
PWV, m/s	9.0 (1.5)	9.0 (1.5)	9.1 (1.5)	9.3 (1.9)	0.55
ABI	1.07 (0.11)	1.06 (0.11)	1.07 (0.10)	1.07 (0.12)	0.62