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

Among 353,708 patients with autoimmune hypothyroidism, 44.8% had a history of psychiatric morbidity prior to diagnosis.

• This was a nationwide retrospective cohort study including all adults in Sweden with autoimmune hypothyroidism initiated on thyroid hormone treatment 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.
• Total cohort size was 353,708 patients.

Patients with preexisting psychiatric morbidity were significantly more likely to receive liothyronine than those without a psychiatric history.

• Adjusted odds ratio (aOR) for liothyronine use among patients with psychiatric morbidity was 1.90 (95% CI 1.83-1.97, P < .001).
• Logistic models adjusted for sex, age, and region.
• The association was described as most evident among individuals with affective or anxiety morbidity (aOR 1.91, 95% CI 1.84-1.98, P < .001).
• No significant association was found for psychotic morbidity (aOR 1.08, 95% CI 0.98-1.19, P = .11).

Preexisting affective or anxiety morbidity was particularly strongly associated with subsequent liothyronine use in autoimmune hypothyroidism.

• aOR for liothyronine use among patients with affective or anxiety morbidity was 1.91 (95% CI 1.84-1.98, P < .001).
• This was the strongest and most statistically significant subgroup association reported in the study.
• The association was distinct from psychotic morbidity, which showed no significant association with liothyronine use.

Psychotic morbidity was not significantly associated with liothyronine use in autoimmune hypothyroidism.

• aOR for liothyronine use among patients with psychotic morbidity was 1.08 (95% CI 0.98-1.19, P = .11).
• This contrasts with the significant associations found for affective and anxiety morbidity.
• The finding suggests differential pathways by which psychiatric subtype may influence treatment decisions.

Autoimmune hypothyroidism affects 1% to 2% of the population in iodine-sufficient areas, and a substantial number of patients report persistent symptoms despite adequate levothyroxine treatment.

• Levothyroxine is described as the standard treatment for autoimmune hypothyroidism.
• Persistent symptoms despite adequate treatment are noted as a known clinical phenomenon.
• The use of liothyronine as an adjunct to levothyroxine therapy has increased.
• The psychiatric characteristics of patients receiving liothyronine were described as 'largely unknown' prior to this study.

The authors suggest that the association between psychiatric morbidity and liothyronine use may reflect persistent symptoms influencing subsequent treatment decisions.

• The authors propose that persistent symptoms in patients with affective or anxiety morbidity may drive clinicians toward liothyronine use.
• The findings raise the possibility that overlapping symptomatology between psychiatric conditions and hypothyroidism contributes to treatment escalation.
• The study design was retrospective and observational, precluding causal inference.