Tension-type headache and migraine are among the top six most prevalent diseases globally, and represent the third cause of disability worldwide in individuals under the age of 50 [14].
In pathogenesis of migraine attacks, the role of hormonal regulation is proved by the presence of its menstrual-dependent variants. But the data about the role of thyroid hormones in migraine not confirmed with many contradictory studies [15]. Hagen and his colleagues found low headache prevalence among patients with hypothyroidism [16] while others observed high prevalence of chronic migraine in patients with hypothyroidism [17]. Migraine, tension headache, and hypothyroidism are clinical problems that affect patient daily activities and quality of live with established comorbidity that has been known for more than 60 years [18, 19].
Hypothyroidism in our study was more common in females than males (in both migraine and tension headache together) although not statistically significant (p = 0.448). The female preponderance in our study was consistent with Khan and his colleagues which found higher prevalence of both migraine and TTH in patients with hypothyroidism [20]. While other study reported that women with hypothyroidism were protected from headache [16].
We have found in our study of 212 patients (migraine and tension headache) that there was significantly higher proportion with subclinical (23.3%) and overt hypothyroidism (6%), as compared to the control subjects of 9% and 1%. This was in agreement with the results from other studies [21, 22].
Lima Carvalho and his colleagues found in a population of 213 patients with de novo hypothyroidism (133 of them with subclinical hypothyroidism) that new onset headache developed in 34% of the patients, with a predominantly migraine phenotype, while 78% of patients (with both overt and subclinical hypothyroidism) treated with levothyroxine for 12 months demonstrated improvement of headache symptoms [23].
In contrast to our findings, a cross-sectional study of 130 out-patient migraineurs revealed abnormal levels of TSH only in 5% of patients, and also that lower TSH values were associated with more prolonged migraine attacks and with a greater impact on quality of life [24].
Moreover, our patients showed significantly more abnormal gland morphology than healthy control on thyroid gland ultrasound. The subclinical and overt hypothyroidism prevalence in our patients with migraine and tension headache were also higher than that reported in the general population. The prevalence of subclinical hypothyroidism in general population ranges from 4-10% [25] and that of overt hypothyroidism is 1-2% [26], and is in agreement with our control group.
In our study, binary logistic regression analysis showed that patients having migraine and TTH were more prone to develop hypothyroidism when compared with control group (BLR = 1.316, 95% CI = 1.82-7.64, p = 0.001). Also patients with chronic TTH are susceptible to develop hypothyroidism (either subclinical or overt) 3.57 times when compared with patients having frequent or infrequent TTH (BLR = 1.272, 95% CI = 1.55-8.22, p = 0.003).
There are several mechanisms that may explain the association between migraine and hypothyroidism. Changes in the immune system that occur as a result of migraine may predispose to thyroid autoimmunity [27].
In addition, migraineurs demonstrate sympathetic hypo function during interictal periods, which may increase the risk for hypothyroidism [28].
Genetic factors, such as hyperhomocystemia and shared environmental factors, including air pollutants and synthetic compounds [29] could also predispose to both migraine and hypothyroidism. Singh proposed a possible pathophysiological link between migraine and hypothyroidism. He suggested that pain is regulated by reciprocal modulation of brain stem serotonergic and noradrenergic nuclei. The failure of one of the two systems implies a compensatory response of the other. Thus, the decreased adrenergic tone in hypothyroidism could upregulate the serotonergic response which causes headache.
In our study, migraine patients were significantly younger than tension type headache patients (p = 0.001). This is in agreement with Okumura and his colleagues [30]. There were no significant differences between both migraine and TTH as regards gender, thyroid function or even abnormal thyroid morphology. About one-third of our patients showed abnormal thyroid function (29.7%) whether subclinical or overt hypothyroidism and only 10.3% of them had abnormal gland morphology, these findings are consistent with many previous observation [31, 32].
In the study of Ekici and Cebeci, subclinical hypothyroidism was found in only (5.1%) of patients with migraine [33] while Parashar and his colleagues did not find any changes in thyroid hormone levels with migraine or TTH [34], Larner did not reveal migraine headache associated with hypothyroidism [35], and hypothyroidism were associated with lower frequency of occurrence of headaches in all age groups [16].
In our study, the frequency of tension headache was 55.7% and migraine headache 44.3% and this observation is partially agreed with Hagen and his colleagues [36] as they reported that prevalence of TTH was 51.9%, meanwhile for migraine was 17.2%. Moreover, Stovner and his colleagues found 11% of their patients had migraine and 42% had tension-type headache [37].
Intragroup comparative analysis of TTH patients revealed that patients with chronic TTH were significantly older than other subtypes (p = 0.010) and have longer disease duration than episodic TTH (p = 0.001). Moreover, 46.3% of those patients suffered from chronic TTH have overt hypothyroidism versus 20% and 19.1% of those with frequent TTH and infrequent TTH respectively (p = 0.009), this is in agreement with Khan and his colleagues reported that frequency of hypothyroidism was more common in chronic TTH as compared to episodic TTH [38]. More recently, Qu with his colleagues [39] observed in chronic TTH there were lower levels of T3 and T4 and higher level of TSH than controls.
Regarding sub analysis of migraine patients, there were no significant differences between migraine with aura, migraine without aura, or chronic migraine as regards thyroid function or morphology (p = 0.137 and p = 0.468 respectively) and this is consistent with a recent Russian study who reported negative results regarding comorbidities of migraine and hypothyroidism with abnormal levels of TSH in only 5% of their migraine patients. On the other hand, many other studies [40, 41] found that hypothyroidism was statistically significantly higher in chronic migraine when compared with migraine without aura but when compared with migraine with aura it was statistically insignificant.