Endocrine Abstracts

Background: Macro-TSH, a rare condition, should be considered in asymptomatic patients presenting with a biological profile of subclinical hypothyroidism, thus avoiding unnecessary treatment. We report the case of a patient with macro-TSH.

Case Presentation: A 41-year-old man was transferred from the Cardiology Department for further exploration of elevated TSH. He has been hospitalized for acute decompensation of heart failure. A thyroid workup revealed a TSH of 45.5 μUI/ml, verified twice after three and six months with normal Free T4 level. There was no history of taking amiodarone or iodized products. The patient had no clinical signs of hypothyroidism on examination. Anti-thyroid peroxidase antibodies and antithyroglobulin antibodies were negative. Ultrasound showed thyroid hypotrophy, and scintigraphy revealed homogeneously increased fixation. The diagnosis of macro-TSH was most likely. Unfortunately we could not find any laboratory that could do TSH chromatography. We decided not to prescribe hormone replacement therapy. The evolution was marked by the persistence of a high TSH without any clinical or biological repercussions.

Discussion/Conclusion: Isolated elevation of TSH in the absence of thyroid symptoms can be very rarely caused by a macromolecule formed between TSH and immunoglobulins (macro-TSH), confounding the interpretation of thyroid function test results. The biochemical profile mimics subclinical hypothyroidism and may lead to inappropriate LT4 treatment. No immunoassay can reveal the presence of macro-TSH. Gel filtration chromatography is the state of-the-art method for detection of macro-TSH. Unfortunately, this test is expensive and not widely available