Results of this study allowed us to estimate the prevalence of thyroid dysfunction in the Polish senior population at 15.5%. In this age group, thyroid dysfunction is about 3-fold greater among women (21.5%), than in men (7.2%), including hypothyroidism in 13.9% (19.4% in women and 6.3% in men) and hyperthyroidism in 1.6% (2.1% in women and 0.9% in men). As expected, these figures are higher than those for the whole European population [10], most possibly due to a different age range. Previous studies reported overt and subclinical hypothyroidism in up to 5.7% and 12.5%, respectively, in older adults in various geographical areas [22, 23]. Noteworthy, recent North American data showed a 24.9% prevalence of total thyroid dysfunction in people aged 65 and over [12].
In our study, 21.9% of subjects with hypothyroidism (18.4% of women and 31.9% of men with this pathology) and 34.2% with hyperthyroidism (24.2% women and 32.4% men respectively) were untreated, which corresponds to 3.2% of all Polish seniors – 4.0% of women and 1.9% of men aged 60 yrs. or above. Our data show a lower prevalence of untreated thyroid dysfunction than 6.7% [10] (with 4.9% of hypothyroidism and 1.7% of hyperthyroidism) reported for the general European population. This discrepancy may result from increasingly frequent use of medical services by older adults, commonly suffering from chronic illnesses. Notwithstanding, the prevalence of unrecognized thyroid disease in the Australian population aged 49 years or older was 3.6% (including 3.0% of those with hypothyroidism) [24], whereas in The Colorado Thyroid Disease Prevalence Study 9.9% of the population has a functional abnormality of the thyroid gland that has been unrecognized [25]. In the latter study, however, no separate analysis for older adults was performed.
The present study shows the spectrum of factors associated with the probability of occurrence of untreated thyroid dysfunction. The strongest factor explaining the lack of treatment was the low utilization of primary health care. This proves that family doctors can effectively diagnose thyroid dysfunction and initiate treatment or referral to an endocrinologist. It was shown that a lack of insurance by affecting utilization of outpatient clinics health care may also influence the diagnosis and treatment of thyroid disorders [26].
A second strongest predictor for untreated thyroid dysfunction was male sex. Typical symptoms of thyroid dysfunction are characteristic for young patients and their occurrence predict more accurate thyroid dysfunction in men, but clinical symptoms are less obvious and illusory in older aged patients [27]. In older subjects, the clinical manifestation of hypothyroidism might be similar to signs and symptoms associated with natural ageing. The symptoms may be limited to weight gain, fatigue, muscle cramps, constipation and skin changes [2]. The multimorbidity and adverse drug reactions can also mask or mimic the signs and symptoms of hypothyroidism. A higher percentage of undiagnosed hypothyroidism in men may suggest poor awareness of thyroid disease in men, strongly affected by up to eight to nine times lower prevalence of hypothyroidism than in women [28].
Difficulties also occur in the diagnosis of hyperthyroidism, as in the older population the most common symptom of thyroid hormones excess are tachycardia or atrial fibrillation or exacerbation of cardiovascular disease [29]. Other symptoms of this pathology are depression, apathy, anorexia, weight loss and fatigue. In our study, the frequency of untreated hyperthyroidism may influence the general health of the patients since untreated thyroid hormones excess may lead to the development of cardiac complications and the loss of bone mass [30] and is, therefore, more dangerous than untreated hypothyroidism, was 34.2%. Moreover, the awareness of atypical symptoms of thyroid dysfunction and their clinical presentation in older patients seem to be insufficient by family doctors. Moreover, men utilize less often visits to their primary care physician. The awareness may be effectively increased by educational programs for patients [31].
The next factor associated with undiagnosed thyroid dysfunction is the age of 75 yrs. and above that is also strongly associated with dependence in activities of daily living which, in turn, can limit access to medical services. Moreover, multimorbidity and atypical clinical manifestation of thyroid disease are also associated with age [2]. Of note, dependence in ADL and dementia were less important than utilization of medical services.
Finally, low educational status increased the risk of undiagnosed thyroid dysfunction and improper treatment [26]. In our study group, poor education was more important than economic status. However, this may be different in other societies in which low economic status corresponds to poor insurance status and, therefore, limits the accessibility to health care systems and laboratory tests.
The results also showed that 9.0% of individuals treated for hypothyroidism and 11.6% treated for hyperthyroidism are not properly managed. The previous studies also showed that almost one-third of the patients with diagnosed hypothyroidism did not have proper hormonal substitution [32]. The clinical consequences of undiagnosed, untreated or undertreated hypothyroidism seem to be especially important in patients with co-morbidities like diabetes mellitus [33] and cardiovascular disease [5]. In addition, hypothyroidism is associated with decreased quality of life [34] and increased mortality [15]. Untreated hyperthyroidism may lead to atrial fibrillation, the development of cardiovascular disease (including cardiomyopathy and heart failure), bone loss and thyroid storm [35]. Notwithstanding, clinical consequences of subclinical hypothyroidism are controversial, especially in the oldest. Even though the recent data negate the benefits from levothyroxine supplementation [36].