Insomnia in probable migraine: a population-based study
The main findings in the present study are as follows: 1) The prevalence of migraine, PM and insomnia in the Korea population was 5.3, 14.1 and 3.6 %, respectively; 2) The prevalence of insomnia among subjects with PM (8.2 %) was not significantly different compared to that among subjects with migraine (9.1 %); 3) Headache frequency and HIT-6 score of subjects were higher among migraine and PM subjects with insomnia compared to those without insomnia.
The 1-year prevalence of migraine (5.3 %) in the present study was lower than in previous studies from European (10–25 %) and North American (9–16 %) countries [1]. However, the 1-year prevalence of migraine in Asian countries was 4.7 to 9.1 %, which were lower compared to that in European and North American studies [32]. The migraine prevalence in our study was similar to previous studies in Asian countries.
The 1-year prevalence rate of PM was 14.1 % in the present study. Previous epidemiological studies have reported 1-year prevalence rates of PM ranging from 4.3 to 14.6 %. Thus, the prevalence rate of PM in the present study was similar to those in the previous studies [18, 20, 33–36].
The prevalence of insomnia (?15.5 ISI score) in the present study was 3.6 %. Insomnia prevalence has been previously reported, ranging from 15.3 to 22.8 % in Asian countries including Korea [37–39]. These findings are inconsistent with the present study. This may reflect different insomnia diagnostic criteria. Most previous population-based studies about insomnia probed insomnia symptoms by asking whether subjects had difficult falling asleep, staying asleep and waking too early in the morning. A previous population-based study reported prevalence of insomnia symptoms at least three nights per week was 17.0 %, but insomnia disorder prevalence based on Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria was 5.0 % in this study [39].
Although the prevalence rate of insomnia was not significantly different between subjects with migraine and PM, the ISI score was significantly different between the two groups in the present study. The difference was associated with the higher prevalence of subthreshold insomnia (8???ISI score???14) among subjects with migraine compared to those with PM. The prevalence rate of insomnia in subjects with migraine and PM was higher compared to non-headache controls in the present study. The finding agrees with findings in previous studies concerning the association between headache and insomnia [3]. Cross-sectional studies showed that headache or migraine had increased ORs compared to non-headache controls and longitudinal studies showed bidirectional comorbidity of two conditions: subjects with insomnia showed an increased risk for headache at 11-year follow up and vice versa [10, 40].
A few studies have addressed the relationship between PM and insomnia among children. Children with adult-like migraine had a higher prevalence of sleep disorders compared to non-headache controls (disorders of initiating and maintaining sleep; migraine 37.1 % vs controls 9.2 %, disorders of arousals; migraine 59.3 % vs controls 10.2 %) [41]. Sleep disorders in infancy could be good predictors for the development of headache [42].
In the present study demonstrated that depression (PHQ-9 score), anxiety (GAD-7 score), headache frequency and headache intensity (VAS score) were independently associated with insomnia (ISI score) among individuals with PM (Table 4). This finding was similar to findings in the previous studies among migraineurs. A study including 78 migraineurs and 208 healthy controls revealed that sleep quality and headache frequency was significantly associated after adjusting anxiety and depression [43]. Another study demonstrated that migraineurs had more sleep problems than healthy controls even after adjusting lifetime anxiety and depression [44].
In the present study, headache frequency and HIT-6 score were higher in migraine and PM subjects with insomnia than in those without insomnia. Since a high headache frequency is one risk factor for chronification of headaches, our finding suggests that insomnia may be associated with the chronification of migraine and PM. We also noted that insomnia was associated with a higher HIT-6 score in subjects with migraine and PM. This finding may imply an increased burden of migraine and PM with the presence of insomnia [45]. Physicians should evaluate accompanying insomnia in subjects with migraine and PM. Careful investigation of the main causes of insomnia including psychiatric co-morbidity is also necessary.
This study has some limitations. First, although the questionnaire in this study was validated for migraine, it was not specifically validated for PM. However, the questionnaire itself was based on ICHD-2 and PM was classified based on the ICHD-2 diagnostic criteria. Second, although this study is population-based and had low sampling error, its statistical power was limited in terms of examining the subgroups. In other words, some results might not have reached statistical significance in subgroup analysis because of the limited sample size.
Despite these limitations, our study has several strengths. First, our study was based on clustered random sampling proportional to the Korean population distribution with low sampling error. This condition allowed us to accurately investigate the prevalence of insomnia, migraine, and PM among the Korean adult population. Second, this study explored the relation between PM and insomnia. This relation has been rarely studied. Third, we investigated both anxiety and depression, which are common comorbidities among subjects with insomnia and migraine, and assessed the effect of anxiety and depression in the association of insomnia with migraine and PM. Balancing the limitations and strengths, we believe that the present study accurately describes the association between insomnia and PM in comparison with migraine.