Neuropsychiatric comorbidities in hypothyroidism: A systematic review

Abstract Objectives Impairment of thyroid function is implicated in different neuropsychiatric manifestations. This systematic review article will examine and discuss (1) the biochemistry of thyroid hormones, including structure, synthesis, and homeostasis, (2) the neurophysiological role of the hypothalamic-pituitary-thyroid (HPT) axis in development and maintenance of a euthymic state, (3) laboratory measures of thyroid function, (4) clinical staging of hypothyroidism, and (5) neuropsychiatric comorbidities of hypothyroidism. Data sources Data sources include a systematic review of English articles using Ovid (1950–2018). Search terms included hypothyroidism, depression, and bipolar disorder. Additional studies were identified and added by searching references of articles in this database. Included topics focused on treatment of neuropsychiatric disorders with psychiatric drugs and adjunctive thyroid hormone replacement. Methods We created the database by identifying articles from multiple sources. Sources included the Ovid database, references of collected articles, and manual retrieval of articles on focused topics. Clinical information was summarized towards review objectives. We include a summary of the relevant basic sciences to enhance a thorough review. Results We found use of adjunctive treatment with thyroid hormone an acceptable approach to treating treatment-refractory or otherwise atypical presentations of mood and cognitive disorders. Given the prevalence of neuropsychiatric symptoms in subclinical hyperthyroidism and the severity and treatment-resistant symptoms, clinicians should rule out thyroid disorders in presentations of a mood disorder. Clinicians should consider an endocrine disruption in psychiatric patients whose mood symptoms remain treatment-refractory. Limitations The article does not discuss hyperthyroidism, which may predicate episodes of hypothyroidism in patients. Only articles with English-language abstract or full text were included. No quantitative synthesis is included as no meta-analysis was conducted. Risks of bias across studies include publication bias and selective reporting. Conclusions Hypothyroidism should be investigated in patients with neuropsychiatric symptoms of mood disorders. Adjunctive thyroid hormone treatment should be considered as a possible option for patients with refractory mood disorders.