Initial disease severity and methimazole titration for Graves' disease: a retrospective longitudinal cohort study.

CONTEXT: Graves' disease (GD) is the most common cause of thyrotoxicosis. Medical therapy with methimazole is the most common way to treat GD, but it has a narrow and dynamic therapeutic index, requiring frequent monitoring for titration. It is unclear how much initial disease severity (IDS) affects titration patterns.

OBJECTIVE

Identify associations between IDS with methimazole dose and thyrotoxicosis control after initiation of therapy.

DESIGN

Retrospective longitudinal cohort study (2018-2024).

SETTING

A single tertiary medical center.

PATIENTS OR OTHER

PARTICIPANTS

The study included 152 patients, aged 18 years and older, diagnosed with GD. It encompassed 1432 encounters.

MAIN OUTCOME MEASURE(S): The analysis focused on the association of IDS, age, and sex with average decrease in methimazole dose per encounter, biochemical thyroid status per encounter, time until first euthyroid encounter, and dose of methimazole after 180 days of treatment.

RESULTS

IDS was positively associated with percentage dose reduction of methimazole per encounter (P = .012) and proportion of hypothyroid encounters (P = .0101). There was no association of IDS with the proportion of hyperthyroid encounters (P = .088), methimazole dose after 180 days (P = .222), nor time to first encounter with euthyroid status. Age and sex were not associated with changes in dose or biochemical thyroid status.

CONCLUSION

When given a larger dose of methimazole, patients with severe thyrotoxicosis from GD reach euthyroid status as quickly as other patients with GD. However, these patients have more lability in thyroid control and may benefit from more frequent monitoring. After 6 months, severity of initial thyrotoxicosis was not associated with methimazole dose.