The primary findings of the present study were the following: (1) approximately one-sixth of individuals with migraine and PM experienced CA, and the prevalence of CA was not significantly different between those with migraine and those with PM; (2) individuals with migraine and PM with CA experienced more severe symptoms and higher impact of headache and disability than those without CA; and (3) headache intensity, anxiety, and depression were significant factors of CA in individuals with PM. In those with migraines, anxiety was a significant factor of CA.
The present study found that 16.0% and 14.5% of individuals with migraine and PM, respectively, had CA. Our results are similar to those of a previous Korean clinic-based study, which reported that CA was observed in 14.5% of patients with migraine . These values were lower than those reported in previous studies from the Western countries. American Migraine Prevalence and Prevention (AMPP) study, a large population-based in USA, reported that 62% of individuals with migraine had CA . Migraine in America Symptoms and Treatment study, another American large population-based study, reported that the prevalence of CA in those with migraine was 40% . A Dutch cohort study revealed that CA was present in 70% of participants with migraine . One possible explanation for the lower prevalence of CA in the present study is the difference in the migraine symptoms in the Asian countries. The symptoms are milder in the Asian countries than in the Western countries. Moderate headache intensity was reported in 30–65% of individuals with migraines in Asian countries [18, 19]. In the Western countries, 80–85% of individuals with migraine reported severe headache intensity [20, 21]. Photophobia was reported in 40–65% of individuals with migraine in Asian countries and 75–85% of individuals with migraine in Western countries [18, 21–23]. Headache intensity and photophobia were reported as significant predictors of CA in individuals with migraine . Therefore, milder headache intensity and lower photophobia might result in lower prevalence of CA. Another possible explanation is the difference in the body mass index (BMI), which has been reported to be lower in Asian populations than in Western populations . High BMI was reported to be a significant factor for CA in the AMPP study . That study found that obese (BMI, 30–40 kg/m2) and morbidly obese (BMI, ≥ 40 kg/m2) individuals had higher risk of CA. In the present study, there was no significant difference in BMI in individuals with migraine and PM according to the presence of CA. This discrepancy might be because of differences in BMI. Only two individuals with migraine and four individuals with PM were obese. Furthermore, none of the individuals with migraine and PM qualified for morbid obesity. Ethnic differences could be another possible explanation. It has been reported that pain sensitivity varies among ethnic groups . Further studies in various migraine populations are required for a better understanding of the prevalence and contributing factors of CA.
In the present study, ‘exposure to cold’ and ‘resting your face or head on pillow’ were most frequently positively responded items in both individuals with migraine and PM. ‘Combing hairs’ and ‘pulling your hair back’ followed the next frequency. Allodynia is classified as mechanical dynamic, mechanical static, and thermal allodynia. They differ in terms of the transmission nerve fibres and nociceptors [26, 27]. Each item of ASC-12 complied three types of CA. ‘Exposure to cold’ and ‘resting your face or head on pillow’ corresponded to thermal allodynia, and ‘combing hairs’ and ‘pulling your hair back’ items corresponded to mechanical dynamic allodynia . High positive response rate to items of thermal and mechanical dynamic allodynia in individuals with migraine was previously reported in a Brazilian study . The present study is the first to identify a high positive response rate to items corresponding to thermal and mechanical dynamic allodynia in individuals with PM, which is similar to that in individuals with migraines.
The headache frequency, headache intensity, disability, and impact of headache were higher in those with migraine and PM combined with CA than in those without CA in the present study. Further, CA was more prevalent in those with the chronic form (≥ 15 episodes per month) of migraine and PM than in those with low headache frequency (< 1 episode per month) (Fig. 2). The close associations of CA with symptom severity and chronicity have been previously reported in migraine [4, 6]. The present study provides evidence that such an association is also present between CA and PM.
In the present study, anxiety and depression were identified as significant factors of CA in individuals with PM. The significant association of anxiety and depression with CA has been reported previously. Kao et al. reported that anxiety was a significant factor of CA using multivariable regression analyses. Furthermore, comorbid anxiety and depression were also associated with the severity of CA . Louter et al. reported that CA was associated with higher prevalence of depression in individuals with migraine . CA, anxiety, and depression a significant risk factor of CM transformation from episodic migraine (EM) [7, 31]. CM has a higher prevalence in the presence of anxiety, depression, and CA than EM . Therefore, our findings added an evidence for the significant association of anxiety and depression with CA and suggested sharing pathophysiological mechanisms of CA with anxiety and depression. Biogenic amines might be involved in a possible shared mechanism. Allodynia is a characteristic of FM, which is a chronic condition of widespread pain . In an animal model of fibromyalgia, decreased tactile threshold was correlated with depressive behaviours . The animal model demonstrated a decreased level of biogenic amines including dopamine, 5-hydroxytryptoptamine, and norepinephrine in the spinal cord, thalamus, and prefrontal cortex.
The prevalence of migraine in the present study was lower than that in previous Western studies. The prevalence of migraine in Asian countries is 3–10%, which is lower than that in Western countries where it is 11–18% . Therefore, migraine prevalence in the present study was similar to those in previous Asian studies. The reported prevalence of PM ranges widely (USA, 4.5%; Singapore, 6.2%; France, 10.0%; Korea. 11.5%; England: 14.6%) [9, 10, 12, 35]; therefore, the prevalence of PM in the present study was broadly similar to those in previous studies. The similarities in the prevalence of migraine and PM between the present and previous studies suggest that appropriate evaluation of migraine and PM in the current study.
The present study has some limitations. First, we used ASC-12 in the evaluation of CA. The gold standard of assessing CA is quantitative sensory testing (QST); it requires specialized equipment and is difficult to conduct in clinical practice and epidemiological studies. ASC-12 was previously validated in comparison with QST . It was also validated in Korean individuals with migraine . Second, we did not investigate the disease durations of migraine and PM. Disease duration was reported to be a significant factor of CA in patients with migraine. Since medical consultation and awareness of migraine diagnosis is not high in Korea, it would be difficult to know participants’ exact disease duration of migraine. We believed that the assessments of disease duration were less feasible and, therefore, did not include them in the analyses. Finally, we did not evaluate the use of medications in the participants. Some medications for migraine prevention, such as serotonin-norepinephrine reuptake inhibitors and anticonvulsants, might relieve CA [36–38]. Further studies on the use of medications are required to provide accurate information of CA in patients with migraine and PM.
The present study includes several strengths. First, we used a two-stage clustered random sampling method proportional to the distribution of the total population of Korea. Furthermore, the estimated sampling error was low. This approach allowed us to successfully assess CA in individuals with migraine and PM in a population-based setting. Second, in the present study, the responses of 12 items in addition to the total score of ASC-12 were analysed. We found that ‘exposure to cold’, ‘resting your far or head on a pillow’, and ‘combing hair’ were the most frequently responses both in individuals with migraine and PM. Third, our study used questionnaires which were specialized validated in Korea language for assessing migraine, anxiety and depression. Such process enabled us to accurately evaluate migraine, PM, anxiety and depression in the present study.