Endocrine Abstracts

Introduction: Amiodarone-induced thyrotoxicosis (AIT) can present a high morbi-mortality.Initial subtype identification facilitates appropriate management.We describe the utility of diagnostic tests in a cohort of patients with AIT.

Material and methods: Retrospective, observational study of 59 patients attended from 2007 to 2018 in outpatient clinic. Differential diagnosis: type I if FT4 and FT3 (TH) were normalized following therapy with antithyroid drugs (ATD)-methimazole alone or with potassium-perchlorate (KClO4); Type 2 if TH were reduced following oral prednisone (Pred) initiation and/or there was a hypothyroid phase following Pred discontinuation without prior AT; Mixed-AIT if patients needed both types of therapy to control TH. Most patients were initially treated with methimazole 30 mg daily unless diagnostic tests (thyroid scintigraphy and Doppler ultrasound) suggested type-2 AIT, where Pred was initiated. KClO4 (1 g/day 6–8 weeks) was associated when other medication was insufficient. Student’s t test, χ² or non-parametric tests.

Results: Males 36 (61%). Mean age: 70 (SD12). Mixed-AIT: 44 (74%) patients, type 1-AIT: 9 (14%), five with prior subclinical hyperthyroidism. Type 2: 6 (10%) patients. Interleukin-6 levels elevated in 50%, 40% and 58% patients in type 1, type 2 and mixed AIT respectively (P=0.7 among groups). Thyroglobulin and/or thyroid-peroxidise antibodies raised in 11% with type 1, 16% with type 2, and 8% with mixed-AIT (P=0.5).Tc-99m-pertechnetate-thyroid scan: no uptake in 39/40(97%). Technetium-99m–sestamibi (Tc-MIBI) thyroid scintigraphy: uptake in 1/3 (33%) type-2 patients, 5/5 (100%) type-1 patients (P=0.035) and 23/27(85%) mixed-AIT patients (P=0.3) showed patchy, diffuse or localized uptake. Colour-Doppler ultrasound: absent vascularity in 2/5 (40%) type-2 patients, 1/7 (14%) type-1 patients, and 23/40 (57%) mixed-AIT patients (P=0.35). Initial FT3/FT4 ratio was higher in type I;median 0.2 (IQR:0.18–0.33) compared to type II, 0.14 (IQR:0.13–0.15) (P<0.0001) and to mixed-AIT:0.16 (IQR:0.12–0.19) (P=0.007). Optimal FT3/FT4 cut-off in ROC-curve to define those who required ATD (type I or mixed-AIT) vs. those only requiring Pred (type II-AIT) was 0.14;sensitivity: 0.65, specificity: 0.6. 17/53 (32%) patients with type I or mixed-AIT required KClO4 to control TH,15/17 (88%) normalising TH with no severe adverse events. In 7/59 thyroidectomy was performed. One patient died from post-operative sepsis.

Conclusions: Diagnostic tests were of limited value for initial AIT classification, showing significant overlap. Initial FT3/FT4 ratio could potentially be useful for differential diagnosis. Response-to-therapy indicated mixed AIT was the most frequent form. KClO4 association was safe and effective in Type I and mixed forms.