Diagnosis of amiodarone-iodine-induced thyrotoxicosis(AIIT) associated with severe nonthyroidal illness

Abstract

A rare case of amiodarone-iodine-induced thyrotoxicosis (AIIT) associated with nonthyroidal illness is reported. Serum total thyroxine (TT4) and free T4 (FT4) concentrations were elevated and serum TSH was undetectable as frequently observed also in euthyroid amiodarone-treated patients. At variance with common forms of AIIT, serum total triiodothyronine (TT3) was reduced due to low-T3 syndrome. The laboratory diagnosis was made on the basis of elevated free T3 (FT3) levels. Thus, in patients with severe nonthyroidal illness submitted to chronic amiodarone treatment, thyroid status can only be determined by free hormone measurement, particularly FT3 in the case of thyrotoxicosis.

2018 European Thyroid Association (ETA) Guidelines for the Management of Amiodarone-Associated Thyroid Dysfunction

“…In rare cases of AIT associated with severe non-thyroidal illness, FT 3 may be normal [26]. The absolute levels of FT 4 and FT 3 at presentation have no discriminatory value between AIT 1 and AIT 2, although they tend to be higher in AIT 2 [1].…”

Amiodarone‐induced thyrotoxicosis: a difficult diagnostic and therapeutic challenge*

“…, 2001). Under these circumstances, measurement of serum FT3 concentration might be useful in establishing the diagnosis of AIT (Balzano et al. , 1987).…”

Therapeutic Plasmapheresis in Amiodarone-Induced Thyrotoxicosis Resistant to Medical Therapy

“…Amiodarone-induced thyrotoxicosis is diagnosed by increased fT4, fT3, and decreased TSH levels. In rare cases, fT3 may be normal due to severe non-thyroidal illness (13). Although the levels of fT4 and fT3 are higher in type 2 AIT, they are not useful in the differential diagnosis, whereas thyroid autoantibody positivity may be beneficial.…”