Endocrine Abstracts

Aim: In the thyrotoxicosis local investigation protocol, Tc99m pertechnetate scintigraphy technetium scan is used to assess the presence of thyroid uptake and both the degree and pattern of uptake. TSH receptor antibodies are used to demonstrate the presence and activity of autoimmune thyroid disease. We audited the utility of these investigations in a series of thyrotoxic patients.

Methods: Forty-nine patients (11 men, 38 women, mean age 47.5±38) were studied, who were in first presentation of biochemically confirmed thyrotoxicosis. Patients were assessed clinically and a clinical diagnosis made based upon history and examination. TSH receptor antibodies and TPO antibodies were measured; a Tc99m pertechnetate technetium uptake scan was performed to assess degree and pattern of uptake.

Results: Of the 49 patients studied, uptake scans was performed on 39 patients; of these, 7 demonstrated low uptake, 1 showed a toxic multinodular goitre, 5 showed an autonomously functioning thyroid nodule (AFTN) and 26 had diffuse pattern of increased uptake. TSH receptor antibodies were measured in 38 patients, and TPO antibodies measured in 46. Our results showed that, when assessing the aetiology of thyrotoxicosis, the TSH receptor antibody has 90.5% sensitivity but only 75.0% specificity when technetium uptake scan was used as definitive diagnosis. TPO antibodies were found to be more specific (100%), but less sensitive (53.8%) in predicting autoimmune thyroid disease.

Conclusion: TSH receptor antibodies have been shown to have a useful role in the monitoring of autoimmune thyroid disease. This test may be positive with AFTN and should be interpreted with other investigations in thyrotoxic patients.