Persistent TSH Suppression in an Older Woman with a Carried-Forward Antithyroid Prescription: A Case Report

Suppressed thyroid-stimulating hormone (TSH) in older adults carries cardiovascular and skeletal risk, and the steps needed to evaluate it are well established. We describe an 83-year-old woman with type 2 diabetes, hypertension, coronary artery disease after bypass grafting, and atrial fibrillation, living in a rural district and educated to primary-school level, in whom these steps were not taken for several years. Between 2019 and 2026, TSH was 0.1 mIU/L or lower on 10 of 11 measurements. Free thyroxine was always within its reference interval; free triiodothyronine (FT3) was normal on most occasions, exceeded the upper reference limit once in 2022, and was not measured at the index visit. Thiamazole had been prescribed briefly in 2019 but remained on her medication list, and at cardiology and ophthalmology visits the low TSH was not pursued because the record showed antithyroid treatment. At a family medicine visit for renewal of her medication reports, review of her past records, a structured medication interview, and national dispensing records showed no continuing antithyroid treatment. Comprehensive geriatric assessment identified malnutrition risk and iron-deficiency anemia as additional explanations for her weight loss. TSH receptor antibody testing, thyroid imaging, and endocrinology referral were recommended. After the risks had been explained, she declined travel and further investigation, and monitoring was arranged locally. The cause of TSH suppression remains unknown, and T3 toxicosis cannot be excluded. The case does not describe a new disorder. It shows how a known diagnostic approach can go unused when care is divided among specialties and the medication list is accepted without checking. It supports reviewing the past record, confirming whether and at what dose a recorded drug is actually taken, informing the patient, and continuing follow-up with explicit criteria for renewed referral when investigation is declined.