Influence of Preexisting Psychiatric Morbidity on Liothyronine Use in Hypothyroidism: A Swedish Nationwide Cohort Study.

Abstract

Background: Autoimmune hypothyroidism is a common endocrine disorder affecting 1-2% of the population in iodine sufficient areas. While levothyroxine is standard treatment, a substantial number of patients report persistent symptoms despite adequate treatment. The use of liothyronine as an adjunct to levothyroxine therapy has increased. The psychiatric characteristics of patients receiving liothyronine remain largely unknown. This study examines the association between preexisting psychiatric morbidity and subsequent liothyronine use in autoimmune hypothyroidism.

Methods: This nationwide retrospective cohort study includes all adults in Sweden with autoimmune hypothyroidism and initiated on treatment with thyroid hormones between 2006 and 2020. Data were obtained from the National Patient Register and the National Prescribed Drug Register. Psychiatric morbidity prior to diagnosis was identified using ICD-10 codes and ATC-codes for psychiatric medications. Logistic models estimated associations, adjusting for sex, age, and region.

Results: Among 353,708 patients, 44.8% had a history of psychiatric morbidity. These patients were more likely to receive liothyronine (adjusted odds ratio (aOR) 1.90, 95% confidence interval (95% CI) 1.83-1.97, p<0.001) compared to those without a psychiatric history. This was most evident among individuals with affective or anxiety morbidity (aOR 1.91, 95% CI 1.84-1.98, p<0.001). No association was found for psychotic morbidity (aOR 1.08, 95% CI 0.98-1.19, p=0.11).

Conclusion: Patients with a psychiatric history before autoimmune hypothyroidism were more likely to receive liothyronine, especially among those with affective or anxiety morbidity. This may reflect persistent symptoms and affect subsequent decisions in the treatment of hypothyroidism.