migraine is the leading neurological cause for seeking medical care , and is associated with significant disability in the sufferer .
the greatest impact is on migraineurs with headaches on more days than not , a condition defined as chronic migraine ( cm ) .
cm is defined as at least 15  days of headache per month in which at least eight of the days fulfill migraine criteria and/or are treated with specific migraine medications , in the absence of a diagnosis of medication overuse headache .
patients with cm often had a history of episodic migraine that began in adolescence or early adulthood , reporting a process of transformation marked by headaches that become more frequent over years . among migraineurs , defining risk factors for cm , or for the progression of episodic migraine to cm ,
identified risk factors include medication overuse , obesity , sleep problems , and psychiatric comorbidity [ 712 ] .
studies in both community and tertiary settings have demonstrated an association between migraine and several psychiatric conditions [ 8 , 9 ] . however ,
the frequency of psychiatric disorders in both setting has not been compared before in a single study .
furthermore , differences in methods of studies based in community or tertiary centers prevent appropriate comparison .
population studies fail to conduct face - to - face assessments , while clinic - based studies carry the potential for selection bias .
studies focusing on best methods to address this gap are of interest , and one strategy is to compare data obtained from the community with those from specialty care , where methods of collection have been virtually identical , and that was the scope of this study .
we compared demographic data and psychiatric comorbidity in a sample of individuals with cm from the community with another from a tertiary care clinic . in light of the fact that patients suffering from migraine and comorbid psychiatric disorders are greater health - care service users
, we hypothesized that the frequency of psychiatric disorders , notably depression , is higher in patients followed in tertiary care .
community data were gathered in capela nova , a city from the state of minas gerais , brazil . according to the 2000 brazilian census , its population was 2,066 inhabitants ( 1,631 over the age of 10  years ) .
the present study is part of an observational , cross - sectional and population - based study conducted in two phases [ 14 , 15 ] .
initially , community health workers from the family health program directly interviewed all inhabitants aged 10  years or older for headache symptoms in the previous year .
the family health program works through family health - care teams which are composed of one physician , one nurse , one auxiliary nurse , and four to six community health workers , and are assigned to specific geographical areas with defined populations of 6001,000 families .
activities provided by family health - care teams take place at primary care facilities , in patients homes , and in the community . in the first phase of our study ( screening phase ) , trained community health workers screened for the occurrence of headaches using the following question :  have you had any headache episode over the last 12  months ? 
those who screened positive were asked about headache frequency in the past month , and those reporting 15  days or more of headache were offered in - person assessment by neurologists with expertise in headache medicine .
three neurologists independently examined participants , and headaches were diagnosed according to the second edition of the international classification of headache disorders .
subsequently , all individuals aged 18 years or older with cm were assessed for psychiatric comorbidities .
psychiatric assessment was performed by an experienced psychiatrist using the mini international neuropsychiatric interview ( mini ) .
the same investigators involved in the community - based assessment used the very same procedures to diagnose consecutive patients attended at a university - based headache center in the first half of 2006 .
this center is located in belo horizonte and is the only headache clinic in the state of minas gerais , brazil .
the study followed the guidance of the regulatory norms of the brazilian national health council ( resolution 196/1996 ) which is in accordance with the helsinki declaration .
the protocol and all forms were reviewed and approved by the local ethics research committee .
data were transferred to epi - info 2000 by a study coordinator and analyzed using spss 12.0 .
the relative frequencies of psychiatric comorbidities were stratified by headache type , and confidence intervals were calculated .
discrete data were compared between groups using the chi - square test or the fisher test ( when anticipated values were small ) . for continuous non - parametric variables , the mann 
community data were gathered in capela nova , a city from the state of minas gerais , brazil . according to the 2000 brazilian census , its population was 2,066 inhabitants ( 1,631 over the age of 10  years ) .
the present study is part of an observational , cross - sectional and population - based study conducted in two phases [ 14 , 15 ] .
initially , community health workers from the family health program directly interviewed all inhabitants aged 10  years or older for headache symptoms in the previous year .
the family health program works through family health - care teams which are composed of one physician , one nurse , one auxiliary nurse , and four to six community health workers , and are assigned to specific geographical areas with defined populations of 6001,000 families .
activities provided by family health - care teams take place at primary care facilities , in patients homes , and in the community . in the first phase of our study ( screening phase ) , trained community health workers screened for the occurrence of headaches using the following question :  have you had any headache episode over the last 12  months ? 
those who screened positive were asked about headache frequency in the past month , and those reporting 15  days or more of headache were offered in - person assessment by neurologists with expertise in headache medicine .
three neurologists independently examined participants , and headaches were diagnosed according to the second edition of the international classification of headache disorders .
subsequently , all individuals aged 18 years or older with cm were assessed for psychiatric comorbidities .
psychiatric assessment was performed by an experienced psychiatrist using the mini international neuropsychiatric interview ( mini ) .
the same investigators involved in the community - based assessment used the very same procedures to diagnose consecutive patients attended at a university - based headache center in the first half of 2006 .
this center is located in belo horizonte and is the only headache clinic in the state of minas gerais , brazil .
the study followed the guidance of the regulatory norms of the brazilian national health council ( resolution 196/1996 ) which is in accordance with the helsinki declaration .
the protocol and all forms were reviewed and approved by the local ethics research committee .
data were transferred to epi - info 2000 by a study coordinator and analyzed using spss 12.0 .
the relative frequencies of psychiatric comorbidities were stratified by headache type , and confidence intervals were calculated .
discrete data were compared between groups using the chi - square test or the fisher test ( when anticipated values were small ) . for continuous non - parametric variables , the mann 
in the community of 1,605 interviewed inhabitants , 57 ( 3.6  % ) had headaches on at least 15  days for at least three consecutive months .
43 ( 75.4  % ) had cm and 41 consented to being assessed by the psychiatrist ( 95.3  % participation rate ) . in the headache center , 43 patients had cm ( n  =  453 , 9.5  % ) and all consented in participating in the psychiatric assessment .
sociodemographic profiles were similar between groups with the exception of the mean number of years of formal education , lower in the community relative to the headache center ( table  1).table  1demographic characteristics in individuals with chronic migraine from the community and a clinic - based samplecommunity ( n  =  41)headache center ( n  =  43)p valuegender  men7 ( 17.1  % ) 2 ( 4.7  % ) 0.09 * *  women34 ( 82.9  % ) 41 ( 95.3  % ) education ( years of study )  826 ( 78.8  % ) 5 ( 11.6  % ) < 0.001 *  9115 ( 15.2  % ) 15 ( 34.9  % )  122 ( 6.1  % ) 23 ( 53.5  % ) age  mean ( sd)41.2 ( 17.2)35.7 ( 12.6)0.19 * * *  range13731863 *  chi - square , * *  fisher , * * *  mann  whitney demographic characteristics in individuals with chronic migraine from the community and a clinic - based sample *  chi - square , * *  fisher , * * *  mann 
whitney among individuals from the community , 65.9  % of cases were diagnosed with any current psychiatric disorder , relative to 83.7  % in those from the headache center ( p  =  0.06 ) .
the relative frequencies of some specific diagnoses were remarkably high in both groups , despite not being statistically different . in the headache center , the most prevalent disorders were simple phobia ( 41.9  % ) , generalized anxiety disorder ( 34.9  % ) and major depression ( 32.6  % ) . in the community ,
the same disorders were also the most common ones : generalized anxiety disorder ( 39.0  % ) , phobias ( 29.3  % ) , and major depression ( 29.3  % ) .
bipolar disorder was not seen in the community and was diagnosed in two cases from the headache center .
the frequency of antidepressants use was similar in the headache center ( 51.2  % ) and in the community ( 44.4  % ) ( p  =  0.51 ) .
table  2 summarizes these data.table  2current psychiatric comorbidities in individuals with chronic migraine from the community and a clinic - based sampleheadache center ( n  =  43)community ( n  =  41)p valueany diagnosis36 ( 83.7  % ) 27 ( 65.9  % ) 0.06*one or two psychiatric diagnoses21 ( 48.8  % ) 16 ( 39.0  % ) 0.36three or more psychiatric diagnoses15 ( 34.9  % ) 11 ( 26.9  % ) 0.42major depression14 ( 32.6  % ) 12 ( 29.3  % ) 0.74*dysthymia9 ( 20.9  % ) 9 ( 22.0  % ) 0.99**bipolar disorder2
( 4.7  % ) 0 ( 0  % ) 0.23**generalized anxiety disorder15 ( 34.9  % ) 16 ( 39.0  % ) 0.69*specific phobia18 ( 41.9  % ) 12 ( 29.3  % ) 0.23*obsessive compulsive disorder9 ( 20.9  % ) 10 ( 24.4  % ) 0.70*somatization7 ( 16.3  % ) 3 ( 7.3  % ) 0.31**eating disorders2 ( 4.7  % ) 1 ( 2.5  % ) 0.99*alcohol abuse0 ( 0.0  % ) 2 ( 4.9  % ) 0.23 * * *  chi - square , * *  fisher current psychiatric comorbidities in individuals with chronic migraine from the community and a clinic - based sample *  chi - square , * *  fisher
to the best of our knowledge this is the first study to compare the frequency of psychiatric comorbidity of cm in community and tertiary care clinic samples .
the frequency of psychiatric disorders in cm was elevated in both settings , tending to be higher in the tertiary care sample .
while psychiatric comorbidity in episodic migraine has been well established in the literature , psychiatric disorders have been less studied in cm .
only a few studies have addressed psychiatric comorbidities of cm in population - based samples , finding increased levels of depression and anxiety disorders even in comparison with episodic migraine patients [ 11 , 20 ] .
one limitation of these studies was the use of self - report questionnaires rather than clinical interview in ascertaining psychiatric diagnosis . in the present study
we found that up to a third of our patients in each setting had depression .
a similar rate was described in the american migraine prevalence and prevention ( ampp ) study , a population - based survey based on mailed questionnaires . in that study ,
depression was assessed by self - report of a physician diagnosis and by the patient health questionnaire ( phq-9)depression module .
one interesting result from the ampp study was that cm patients were twice as likely to have depression as assessed by phq-9 in comparison with episodic migraine patients [ 30.2 and 17.2  % respectively ; or ( 95  % ci )  =  2.0 ( 1.67 to 2.40 ) , p  <  0.001 ] .
cm patients were also approximately twice as likely to report anxiety [ 30.2 vs. 18.8  % respectively ; or ( 95  % ci )  =  1.8 ( 1.51 to 2.15 ) , p  <  0.001 ] .
the international burden of migraine study ( ibms ) also found higher levels of anxiety and depression in cm when compared with episodic migraine .
regarding anxiety syndromes , generalized anxiety disorder and phobias seem to be comorbid with the migraine spectrum [ 2024 ] .
interestingly the frequency of obsessive  compulsive disorder was significantly high ( between 20 and 25  % ) in cm patients in comparison with its prevalence in the general population ( 2  % ) .
only few previous studies have pointed out this association between obsessive  compulsive disorder and migraine that may be associated with underlying serotonin system dysfunction .
bipolar disorder is also comorbid with migraine ; migraineurs without aura are 2.4 times more likely to have bipolar disorder type 1 , and the ratio increases to 7.3 when the diagnosis is migraine with aura [ 13 , 22 ] . for bipolar disorder type 2 ,
we failed to detect this association , likely because of small size of the samples .
drug abuse has not been traditionally associated with migraine [ 22 , 24 ] , but a recent study reported that illicit drug abuse may be more frequent in migraine patients with depression or post - traumatic stress disorder .
demographic profiles were similar in both groups , and the vast majority of individuals with cm were women .
it must be highlighted that the assessed community was from a small city , while the patients at the headache center mainly came from a large urban center .
nonetheless , studies of migraine that have enrolled subjects with different demographic features also found striking similarities regarding the risk of psychiatric comorbidities , once more pointing to shared biological factors as a plausible mechanism for the comorbidity [ 22 , 24 ] .
specific genotypes coding d2 dopaminergic receptors , dysfunction in tyramine conjugation , changes in the metabolism of serotonin and catecholamines and in estrogen levels have been considered to explain the comorbidities [ 2730 ] .
it is worth mentioning , however , that we have comprehensively and systematically assessed almost all patients with cm from an entire population of a small city .
we did not assess the differential disability associated with headache and psychiatric disorders in the individuals .
finally , our findings were not adjusted for other confounding factors , such as parameters of headache severity ( intensity , duration associated symptoms ) , obesity , sleep disorders , use of psychotropic medication and household income .
we partly justify these latter limitations by arguing that the demands on patients and resources in conducting these missing assessments could jeopardize the community assessment , since most interviews were conducted in participant households . in conclusion
, the present study suggests that psychiatric comorbidity in cm is elevated in the community and clinical settings , tending to be more common in cm patients from a headache center .
 although the association between episodic migraine and psychiatric comorbidities is well documented , few studies have focused on the comorbidity with chronic migraine ( cm ) and discrepancies exist between population - based and clinic - based data . 
 the objective of this study is to compare demographic and psychiatric comorbidity correlates between cm samples drawn from the community and tertiary care . 
 all inhabitants from a city borough were interviewed for the presence of headaches occurring 15 or more days per month . 
 cm was diagnosed after subjects had been interviewed and examined by a headache doctor . 
 participants were also assessed with a structured interview by a psychiatrist , who assigned diagnoses based on the dsm - iv . 
 the same investigators assessed all patients consecutively seen in a university - based outpatient headache center over a 4-month period . 
 the samples consist of 41 individuals from the community and 43 from the headache center . 
 sociodemographic profiles were similar between groups with the exception of the mean number of years of formal education . among individuals from the community , psychiatric diagnoses were present in 65.9  % of cases , relative to 83.7  % in those from the headache center ( p  =  0.06 ) . 
 phobias ( 41.9 vs. 29.3  % ) and depression ( 32.6 vs. 29.3  % ) were more frequent in patients from the headache center , but this difference did not reach statistical significance . 
 thus the frequency of psychiatric disorders in patients with cm was elevated in both settings , being higher in the specialty care clinic . 
Introduction
Methods
Population study
Clinic study
Statistical analysis
Results
Discussion