A nationwide survey of migraine in France: prevalence and clinical features inadults

Patrick Henry1, Philippe Michel1,2, Bruno Brochet1, Jean François Dartigues1,2, Sylvie Tison2, Roger Salamon2, and the GRIM3

Service de neurologie, Hôpital Pellegrin, Bordeaux, France1; Unité INSERM 330, Université de Bordeaux II,Bordeaux, France2; Groupe de Recherche Interdisciplinaire sur la Migraine, Paris, France3

Cephalalgia Henry P, Michel P, Brochet B, Dartigues JF, Tison S, Salamon R, and the GRIM. A nationwidesurvey of migraine in France: prevalence and clinical features in adults. Cephalalgia1992;12:229-37. Oslo. ISSN 0333-1024

In November 1990 a nationwide survey of migraine was conducted in France on a representativesample of residents aged 15 years and older. The diagnosis of migraine was based on theInternational Headache Society (IHS) classification. In a previous study, we validated a diagnosticalgorithm which classifies headache sufferers as IHS migraine, "borderline" migraine, possiblemigraine and non-migrainous headache. The overall prevalence of migraine patients with the IHScriteria in the present study was 8.1%; another 4% were classified as "borderline" migraine, whichwe in fact considered as definite migraine. Age, gender and occupation were found to be riskfactors for migraine. Neither frequency and duration of attacks nor length of time of diseasediffered with gender. Expressed intensity of attacks, however, was greater in females. •Diagnosis, epidemiology, migraine, prevalence, risk factors

P Henry, Service de neurologie, Hôpital Pellegrin, 33076 Bordeaux, France. Received 31December 1991, accepted 27 March 1992

Although migraine is one of the most common pathological disorders, the prevalence of the disease remainscontroversial. Prevalence rates of migraine vary considerably in the literature from 3.1% (1) to 26% (2). Thesedifferences may be explained by selection bias in the studied sample and by a lack of validity of the diagnosticcriteria. Population-based studies are generally void of selection bias, but the accuracy of diagnosis is oftenunsatisfactory (3, 4). Most of the studies use the Gowers definition (5), the Waters definition (6), or the criteria ofthe Ad Hoc Committee of the National Institutes of Health (NIH) (7).

In 1980, we elaborated and validated a standardized questionnaire and a diagnostic algorithm which can beapplied by lay interviewers in epidemiological studies (8). The prevalence of migraine was estimated in this way at10.1% in a sample of 3,000 workers. In 1990, we adapted this algorithm, taking into account the classification ofthe International Headache Society (IHS) (9). The validity of the diagnosis of migraine by lay interviewers wascomputed and compared with that of a senior neurologist on 96 headache sufferers, including 59 migraines and 37other headaches, detected during their systematic annual occupational medical check-up. The headache suffererswere screened by the question "Are you subject to headache?", which is understood in France as "Have yousuffered repeatedly from headaches during the past few years?", to rule out the acute headache related to localdisorders, and evolutive headache. The questionnaire and the algorithm (see Appendix) used the criteria A, B, Cand D of the IHS criteria for migraine. Sensitivity for the diagnosis of migraine was 95% and specificity 78% (10).

The aim of the present study was to estimate the prevalence of migraine, to determine the sociodemographicrisk factors (age, gender, occupation and region) and to analyse the clinical features of the disease by using ourdiagnostic procedure on a representative sample of the general population of the whole of France.

Methods

Sample

The epidemiological survey was carried out by the Institut Français d'Opinion Français (IFOP), a national publicopinion poll agency. A nationwide representative sample of 4,204 subjects in France aged 15 years and older wasconstituted according to the quota method (11), a stratified non-random sampling method. The French populationwas stratified by gender, age (< 25, 25 to 34, 35 to 49, 50 to 64, > 64 years), occupational categories defined bythe Institut National de la Statistique et des Etudes Economiques (INSEE) (12) and the population of place ofresidence ( < 2,000, 2,000 to 19,999, 20,000 to 99,999, ³ 100,000 inhabitants). The quota was the number ofsubjects per stratification. Over the whole of France, each of the 2,000 professional interviewers of the IFOP wasresponsible for fulfilling the quota in their defined area, during a "random route" (13). In each household theyselected and interviewed one subject of the required age, gender and occupation.

Data collection

The data were collected in the home, during face-to-face interviews, in two stages. First, in the screening stage,the headache sufferers were detected in the total sample of 4,204 subjects by two questions: "Are you subject toheadache?" and "Is the frequency of your headaches very rare, rare, frequent, or very frequent?" Age, gender,occupation and place of residence of the subjects were noted.

Among the 1,371 (35%) subjects complaining of headaches, 1,320 had rare, frequent or very frequentheadache and were eligible for the second stage. Subjects with very rare headaches were excluded. Among these1,320 subjects, 1,000 (75.8%) were randomly chosen for a second interview within one month of screening. Onehundred and eleven (11.1%) refused to participate and 56 (5.6%) were in fact found at the second interview not tosuffer from headaches. Thus, 833 subjects were included in the final sample. They were reinterviewed at theirhome by the same investigator. During a 90 min interview using the validated questionnaire for the diagnosis ofmigraine, data were obtained on the severity of the headaches, on sociodemographic and economic status, onquality of life along with use of medical services.

The validated algorithm classified the headache sufferers within four groups: (i) IHS migraine strictlycorresponding to IHS criteria (ii) "borderline" migraine, where either the duration of attacks was between 2 and 4 h,or there was photophobia or phonophobia, (iii) possible migraine, where at least two IHS criteria were missing (thisgroup consisted mainly of "mixed" headache, i.e. patients with migraine attacks and tension headache), and (iv)non-migraine headache. IHS and "borderline" migraine were considered as definite migraine, as their sensitivity andspecificity for the diagnosis of migraine are similar (10). No attempt was made to divide cases into those with andthose without aura as this differentiation was found by the validation study to be non-reliable (10) because migrainesufferers often cannot distinguish unilateral sensory disturbances from nocturnal acroparaesthesia, and scintillatingscotoma from photophobia.

Finally, clinical features of migraine were also noted: frequency of migraine attacks ( < 5 attacks per year, 5 to10/year, 1/month, 1/fortnight, 1/week, 2 to 3/week, >/week); intensity of pain (self-defined items: mild, moderate,severe, very severe); mean duration of attacks in hours; length of time of the disease in years.

Data analysis

Taking into account the possible lack of representation of age and gender in the final sample, an estimatedprevalence of migraine in France was computed: for each gender, the age-specific observed prevalence wasmultiplied by the proportion of the French population in the specific age groups. That is,

mi niPi = ------ * -----

M N

where: Pi is the age and gender-specific adjusted prevalence; mi is the number of age and gender-specificmigraine sufferers interviewed in the final sample; M is the age and gender-specific number of subjects interviewedin the final sample; ni is the size of the French population in the specific age and gender groups; N is the totalFrench population aged 15 years and older.

mi was corrected for the proportion of subjects who met the screening criteria (i.e. were eligible for reinterview)and who were either not sampled (n = 320) or refused to be reinterviewed (n = 111), assuming that these subjectsdid not differ on their disease status from the 833 who were reinterviewed.

Adjustment for age and gender of estimated prevalence by region and occupation was computed using thedirect standardization method. The reference population was the population of France. Place of residence wasclassified into eight regions (North, Paris, Bassin Parisien, West, South-West, Mediterranean, Middle-East, East).The analysis of occupation was limited to six categories (blue-collar workers, white-collar workers, top executivesand secondary school teachers, craftsmen and shopkeepers, farmers, nurses, primary school-teachers and middleexecutives). The standardized estimated prevalence was not computed for the occupational category "housewives,students and unemployed", because the age and gender distributions did not adequately overlap with those of theother categories. A rough estimate of the prevalence was then computed, as for the more detailed classification ofoccupation. Chi square and adjusted chi square, t test and ANOVA were performed to compare the differentdistributions.

Results

Representativity of the sample

The screening sample of 4,204 subjects was not strictly representative of the general population according toage (chi square = 5.5, df = 4, p = 0.02) and occupation (chi square = 118, df = 6, p < 0.001) (Table 1). The genderand residence area distribution for the general population and for the screening sample was not statisticallydifferent. The final sample was representative of the headache subjects of the screening sample with respect toage and occupation but not with respect to gender (chi square = 16, df = 1, p < 0.001) and residence area (chisquare = 22, df = 7, p = 0.01) (Table 1).

Table 1. Comparison of the distributions of quota variables in the total screening sample (%).French

populationEligible for Total aged 15

Final second screening years andsample interview sample older*

Total 833 1,320 4,204 43,000,000GenderMale 29.0 32.8 47.3 47.9Female 71.0 67.2 52.7 52.1Age15 - 25 20.3 21.5 19.3 19.325 -34 27.6 24.8 21.8 19.635 - 49 26.2 27.1 23.4 23.450-64 16.7 16.2 19.6 21.3³ 65 9.2 10.4 15.9 16.4OccupationFarmers 2.2 2.1 3.1 4Craftsmen,shopkeepers 3.4 2.9 3.7 5Managers,professionals 3.6 3.4 3.9 5Nurses, primaryschool-teachers,middle executives 10.6 9.9 10.4 10White-collars 21.8 20.8 16.5 15Blue-collars 12.6 13.2 14.5 19Inactives,housewives,students 45.9 47.5 47.7 42RegionParis 12.5 18.5 18.4 18.7North 7.2 6.6 7.3 7.0East 10.3 9.7 9.0 9.0Bassin Parisien 18.7 18.5 18.8 18.1West 14.6 12.7 12.3 13.1South-West 12. 1 11. 1 10.8 10.8South-East 10.9 10.6 11.8 11.7Mediterranean 13.3 12.5 11.6 11.6* Institut National de la Statistique et des Etudes Economiques (1989)

Prevalence of migraine

Of the 833 cases of the final sample, 230 (27.6%) were classified by the algorithm as IHS migraine, 110(13.2%) as "borderline" migraine and 283 (34.0%) as possible migraine. Two-hundred-and-ten (25.2%) hadnon-migraine headache. Estimated prevalence in France of IHS migraine was 8.1% and that of "borderline"migraine 4.0% (Table 2). The prevalence of definite migraine (IHS and "borderline") was thus 12.1%. Definiteand possible migraine grouped together had a total estimated prevalence of 22.6%.

Prevalence of IHS migraine was 4.0% in men and 11.9% in women. Prevalence of definite migraine was6.1% in men and 17.6% in women. The female/male ratio was 3.84. The prevalence of migraine was highestbetween ages 30 and 39 in both genders. Variation of prevalence according to age for females

Table 2. Prevalence rates of migraine in the Frenchpopulationaged 15 years and over (%).

Males Females Total 95% CIIHS migraine 4.0 11.9 8.1 [6.2-10.0]Borderline migraine 2.1 5.5 4.0 [2.7-5.3]IHS + borderline 6.1 17.6 12.1 [9.7-14.5]migraine(definite migraine)Possible migraine 8.2 12.6 10.5 [ 8.3 - 12.9]Non-migraine 7.3 9.0 8.2 [6.0 - 10.9]headache

was found not to be significantly different to that of males, whether using IHS or definite criteria (Table 3).

Table 3. Prevalence rates of IHS and definite migraine according to age and gender (%).IHS migraine Definite migraine

Age Males Females Both Males Females Both15 - 19 4 6 5.0 5 11 8.020-29 5 12 8.5 8 18 13.030-39 7 19 13.0 9 26 17.540-49 3 17 10.0 6 25 15.550-59 5 12 8.5 6 19 12.560-69 2 5 3.0 2 8 5.070 - 79 3 7 5.5 3 8 6.0> 80 3 3 3.0 3 6 5.0

Variations of standardized prevalence according to place of residence were not significant (chi square =5.4, df = 7, p = 0.6) (Fig. 1).

Standardized definite migraine prevalence was significantly different according to occupation categories(chi square = 54, df =5, p <0.001). The crude prevalence was highest among the primary school-teachers(24.4%) and nurses (21%), and lowest among unskilled blue-collar workers (6 to 9.4%) (Table 4).

Clinical features of definite migraine (Table 6)

Forty-three percent of males and 58% of females had one or two attacks per month, but this differencewas not statistically significant (chi square = 9.8, df = 7, p = 0.2). The attacks were assessed as being severeby the great majority of subjects. The severity was expressed as greater by females than by males (chisquare = 9.7, df = 4, p = 0.05). Finally, no significant difference was found between males and females forduration of attacks (chi square = 8.0, df = 8, p = 0.4) and length of time of disease (t = 0.23, p = 0.8). Meanlength of time of disease was 12.0 ± 3.0 years in males and 11.2 ± 1.6 years in females.

The three diagnostic groups (definite, possible and non-migraine) were globally different for gender (chisquare = 21, df = 2, p < 0.001), intensity (chi square = 125, df = 8, p < 0.001), frequency of attacks (chisquare = 55, df = 14, p < 0.001) and for length of time of the disease (F = 4.6, p < 0.01). For distribution ofage (t = 0.36, p = 0.7), gender (chi square = 0.05, df = 1, p = 0.9), intensity (chi square = 2.1, df = 4, p = 0.07)and frequency of attacks (chi square = 8.4, df = 7, p = 0.3), length of time of the disease (t = 0.14, p = 0.9)and frequency of aura (chi square = 0.05, df = 1, p = 0.9), no significant difference was found between theIHS and "borderline" groups (Table 6).

Discussion

Our study, the first nationwide survey of migraine in France, confirmed that migraine is very common. Theoverall prevalence of migraine with the IHS criteria was 8.1%; another 4% were classified as "borderline"migraine, which we in fact considered as definite migraine.

We have applied the quota sampling method, which is not often used in epidemiological studies. This isthe most common non-random sampling method and was developed in market and opinion research formaximum accuracy over a very short time and at relatively low cost (11). There are many minor differencesbetween quota and random sampling, but the essential one is that in random sampling the selection of thesample units is carried out by some impersonal, strictly determined method, whereas, in quota sampling,once the quota are determined by IFOP and each investigator is given

Table 4. Definite migraine: crude and standardized by age and gender prevalence tabulated according to occupation.Percentage of 95% CI of

Occupational female Mean age Crude Standardized standardized Crudecategories (95% CI)* (95% CI)* prevalence prevalence prevalence Occupation prevalenceNurses, primary [58-78] [33.5-38.1] 18.9 18.3 [14.7-21.9] Primaryschool-teachers, school-teachers 24.4middle executives Nurses 21.0(n = 88) Private middle

executives 19.6Public middleexecutives 15.7Technicians 11. 7

Craftsmen, shopkeepers [40-76] [36.3-43.8] 16.8 15.6 [9.7-21.4] Shopkeepers 17.5(n = 29) Craftsmen 17.5

Private managers 11.4Farmers (n = 18) [32-78] [41.9-53.7] 12.1 11.8 [6.4-17.2]Blue-collar workers [26-441 132.5-36.6] 9.9 10.5 [6.6-14.3] Skilled blue-collar(n = 105) workers 11.1

Farm workers 9.0Unskilled blue-collarworkers 7.6

Housewives, students, [86-94] [32.3-35.7] 14.2 /** /** Housewives,unemployed unemployed 15.4(n = 274) Students 10.6White-collar workers [79-90] [31.4-34.9] 12.7 9.4 [7.4-11.3] Public white-collar(n = 182) workers 14.5

Private white-collarworkers 12.6Domestic serviceemployees 11.0

Top executives and [26-44] [35.6-41.6] 13.0 11.6 [6.8-16.3] Secondary andteachers (except) university teachers 16.7primary) (n = 29) Top executives 9.0* 95% CI: 95% confidence interval; ** No gender overlap.

Table 5. Clinical features of definite migraine according togender(%).

Males Females Both gendersFrequency of attacks< 5/year 7 3 45 to/O/year 18 11 131/month 26 34 321/2 weeks 17 24 231/week 20 15 172 to 3/week 9 8 8> 3/week 0 3 2Do not know 3 2 2Total 100 100 100Intensity of attacksMild 10 4 7Moderate 21 15 19Severe 49 46 48Very severe 20 35 26Total 100 100 100Duration of attacks2-4 h 29 24 254-6 h 24 17 196-12 h 12 12 12About one day 23 24 24About two days 10 9 9About three days 1 8 6Do not know 1 6 5Total 100 100 100Length of the disease (years)0 - 10 40 41 4111-20 30 32 3121-30 16 14 1531-40 7 6 641-50 3 4 451 - 60 1 3 261-70 3 1 1Total 100 100 100

their assignment, the choice of the sample units to fit into the quota is left to the investigators (13). Here, this potential selectionbias was reduced by the use of professional investigators. The quota method does not need the response rate of the screeningstage because its only requirement is to fulfil the quota. The quota theory indeed assumes that if the quota variables are relevant,i.e. are highly correlated with headache and migraine, there is no difference between all subjects of a defined stratum forheadache and migraine status (13, 14). Here, age and gender, two of the variables of IFOP, were the main risk factors forheadache and migraine (15). Last, no complete sampling database was available. The quota method was thus chosen.Eliminating very rare headache excludes subjects who have had one or two attacks in the previous few years, leading to a slightunderestimation of prevalence. Nevertheless, this minor part of the migraine population cannot be considered as a Public Healthproblem.

The 8.1% prevalence of IHS migraine is consistent with the findings of the two recent studies based on the IHS definition ofmigraine, although at the lower range of the results reported by Ensink (16). He found a prevalence of 12% on a 9,000-subjectsample representative of the general population of Canada, Great Britain, Belgium, Sweden and Italy. However, this rate isdifferent from one country to another (from 8% in Great Britain to 19% in Italy). Stewart et al. reported a prevalence of frequentmigraine at 14.6% for females and 4.8% for males from a "9,500 household sample" (17).

The prevalence of migraine reported in previous general population surveys in occidental countries and Israel is between 10and 26%, and the female to male ratio is between two and three (2, 18-21). Abramson et al. (21) found the lowest prevalence ofmigraine (10.1%) but also reported a high (25.6%) prevalence of non-migraine headache. We believe that mixed headache, i.e.both migraine and tension headache, was classified by Abramson as non-migraine headache, whereas in our study it wasclassified in the possible migraine group. The 26% prevalence found by Waters is probably due to a broad definition of migraine(unilateral headache with nausea and warning signs) (2). In our study, the prevalence of the definite and possible migraine was22.2%, which was not very different from Waters' finding. Our more precise diagnostic tool then gives one possible explanation forthe wide variation in prevalence in the literature. In other parts of the world, the prevalence rates seem to be lower than 7%(23-27), except in the most recent study from Thailand, at 12% (28).

Risk factors for migraine were found in our study to be age, gender and occupation. In contrast to widespread opinion inmedical circles, migraine was found to be more frequent in the broad occupational category constituted by nurses, primaryschoolteachers and middle executives than in the category constituted by top executives. Opinion may have been biased as topexecutives tend to consult more often.

In this study, the clinical features were found to be no different with regard to gender, except intensity of pain. Because we didnot adjust for differences in age, these results could be confounded by age, as migraine is strongly associated with this variable.Attacks were expressed as more intense by females than by males, which is consistent with previous studies (22, 24, 29, 30). Thenumber of migraine attacks by duration of attacks describes a bimodal curve. This may reflect two distinct populations: thesubjects who treated their pain effectively at the onset of attacks and those who did not treat their headache or whose treatmentwas ineffective.

We observed in a validation study that the IHS criteria allowed the diagnosis of a very homoge-

Table 6. Main demographic and clinical features in IHS, borderline, definite, possible andnon-migraine groups.

Definite migraineBorderline (IHS + borderline) Possible Non-migraine

IHS migraine migraine migraine migraine headacheSize 230 110 340 283 210Age 38.8±0.9* 38.8±1.4* 38.8±1.1* 38.1±1.1* 41.2±1.3*

Gender% of females 79.9 78.2 79.3 67.5 61.8Intensity of attacks (%)Mild 3 5 4 6 15Moderate 19 25 21 44 54Severe 57 53 55 40 26Very severe 20 16 19 9 3Do not know 1 1 1 1 2Total 100 100 100 100 100Frequency of attacks (%)< 5/year 5 2 4 6 85 to 10/year 13 14 13 16 241/month 31 35 32 27 231/2 weeks 22 23 23 14 171/week 18 14 17 13 112 to 3/week 9 5 8 11 7> 3/week 1 5 2 11 7Do not know 1 2 1 2 3Total 100 100 100 100 100Length of disease(in years) 18.8±1.0* 17.0±1.2* 18.1±1.0* 14.6±1.1* 14.6±1.0*

* Mean standard error.

neous group, but were too restrictive for the diagnosis of all cases of migraine in the general population (10). Wethen developed a diagnostic tool which allows us to distinguish between several migraine groups. The IHS and"borderline" cases were all considered, by the neurologists involved, as definite migraine. This epidemiological studyconfirmed that the two groups may be the same clinical entity, because they were not significantly different withrespect to the main clinical and demographic variables and because the distribution of these variables in the definitemigraine group was different from that of the possible and non-migraine groups.

In conclusion, the prevalence of migraine in France was calculated at 8.1% or 12.1%, depending on whichdiagnostic criteria were used (IHS or our own, respectively). The IHS criteria are certainly useful for cross-nationalstudies and clinical trials, but an estimation of the migraine prevalence based on these criteria seems to imply anunderestimation of about 33%.

Acknowledgements.-This study was supported by a grant from the Glaxo Laboratories, France.

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Appendix I

Interview questions of the validated questionnaire used for algorithm diagnostic of migraine.1. Are you subject to headache? [(1) Yes; (2) No]2. Do you suffer from headache every day? [(1) Yes; (2) No; (3) do not know]3. How long are your headaches usually, without medication? [(1) less than 4 h; (2) between 4 and 72 h; (3) more than 72 h;

(4) do not know]4. What is the usual location of your headaches? [(1) strictly unilateral; (2) alternately in the right and left part

of the head; (3) other location; (4) do not know]5. Pulsating type of headaches? [(1) Yes; (2) No; (3) do not know]6. Do your headaches inhibit or prevent daily activities? [(1) Yes; (2) No; (3) do not know]7. Do your headaches get worse during physical activity? [(1) Yes; (2) No; (3) do not know]8. Are your headaches accompanied by nausea or vomiting? [(1) Yes; (2) No; (3) do not know]9a. Are your headaches accompanied by photophobia? [(1) Yes; (2) No; (3) do not know]9b. Are your headaches accompanied by phonophobia? [(1) Yes; (2) No; (3) do not know]10. Have you had more than 4 attacks in your lifetime? [(1) Yes; (2) No; (3) do not know]