MON-389 - Individualizing Hypothyroidism Care: Case Examples of Triiodothyronine (T3)-Containing Therapy in Clinical Practice

Endorsed by major thyroid professional associations, levothyroxine (LT4) monotherapy has been the standard of care for hypothyroidism for decades. While most patients respond well to this treatment strategy, around 20% report clinical symptoms that could be consistent with the persistence of hypothyroidism despite in-range thyrotropin (TSH) levels. Although the underlying cause remains to be elucidated, emerging evidence suggests that triiodothyronine (T3)-containing therapies, such as desiccated thyroid extract (DTE) or LT4 plus liothyronine (LT3), may improve persistent clinical symptoms. We describe four anecdotal cases illustrating individualized use of T3–containing therapies, including DTE and LT4 + LT3 therapy, in patients with persistent symptoms despite being on TSH-normalizing LT4 monotherapy.

Four female patients with primary or post-surgical hypothyroidism (age: 36-57 years) reported experiencing symptoms that included fatigue, weight gain, and cognitive dysfunction. At the time of the report of symptoms, all 4 patients were treated with LT4 alone for their hypothyroidism and had normal serum TSH. These patients chose a trial of T3-containing therapy (3 DTE, 1 LT4 + LT3). After this treatment switch, all patients reported significant subjective symptom improvements during their follow-up visits. All 3 patients on DTE had in-range TSH (0.40-4.50 mIU/L), with values ranging from 0.76 to 2.30 mIU/L. They also had within range free thyroxine (fT4) levels, with 2 patients having slightly lower fT4 values on DTE (patient 1: 1.6 [reference range: 0.80-1.80] ng/dL; patient 2: 0.95 [reference range: 0.89-1.80] ng/dL) vs LT4 (patient 1: 0.8 ng/dL; patient 2: 0.52 ng/dL). While on DTE, 2 patients had total T3 levels within the reference range (76-181 ng/dL), and 1 had marginally elevated levels (185 ng/dL). In the only patient on LT4 + LT3 therapy, her TSH fell below the reference range ( < 0.01 mIU/L) following initiation of LT3 (5 mcg/day). Out of an abundance of caution, her LT3 dose was adjusted to 2.5 mcg/day, and her TSH returned to normal (0.95 mIU/L) at the next follow-up. No adverse effects were reported, and all patients have continued on their respective T3-containing therapies.

Collectively, these cases underscore that select patients, when given a therapeutic trial of T3-containing thyroid hormone replacement regimens, can experience subjective symptomatic benefit. We provide these cases as examples of dosing strategies and patient eligibility, emphasizing the roles of shared decision-making and patient preference when considering treatment options.

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