Endocrine Abstracts

Background: Some forms of thyroid disease (TD) pose significant diagnostic difficulties. A national rare thyroid disease service (RTDS) was established in Ireland (population 5.2m) in 2020. Operating quarterly, it accepts nationwide referrals from primary care practitioners and specialists for patients with confirmed/suspected complex/rare TD.

Methodology: Clinical note review of attendances at RTDS in first 4 years (January 2021 - October 2024) to determine referral sources, practice volume, patient demographics, and final diagnoses.

Results: 71 patients attended. The average age was 42.6 years, the majority were female (69%). Referrals were from endocrinologists (adult 87%; paediatric 4%) and primary care (9%). Most were from Dublin and surrounding counties (86%). On average 10.8 people attended each clinic; each patient had 2.4 visits on average. 46% of patients were referred with discordant TFTs, 25% with complicated hypothyroidism (abnormal TFTs, reset HPT axis in congenital hypothyroidism, thyroxine malabsorption, etc), 15% with complicated hyperthyroidism (fluctuating TRAb, unknown aetiology, etc), 10% with suspected assay interference and 3% with known Resistance to Thyroid Hormone. Patients received a diagnosis within 2 visits. Most (72%) had specialised testing at a reference laboratory and genetic testing was performed in 45%. A formal diagnosis was established in 97% of patients, investigations are ongoing in 3%. Complicated hypothyroidism (25%), T4 assay interference (20%) and complicated hyperthyroidism (17%) were the most common diagnoses. Cases of RTH Beta (10%), Familial Dysalbuminaemic Hyperthyroxinaemia (6%), TSH assay interference 4%, TTR mutation 4%, drug induced TD (4%), TSHoma (1%) and non-thyroidal illness (1%), were also identified. Less commonly, some individuals were found to have no identifiable TD (4%).

Conclusion: The spectrum of TD diagnosed and managed at the RTDS is highly variable. Access to a specialist clinic linked with appropriate specialist biochemical support and genetic testing facilitates timely diagnosis and appropriate management of complex and rare TD.