Endocrine Abstracts

Background: Accurate diagnosis of an underlying cause of thyrotoxicosis is critical for targeted therapy. Thyroid radionuclide uptake scan is a useful second line investigation in patients who lack TSH receptor antibody. The uptake scan patterns identify patients who can be preferentially treated with anti-thyroid drugs (diffuse pattern - Graves’ disease) or radio-iodine treatment (patchy uptake - multinodular or localised uptake – toxic adenoma) or simple monitoring (no update – thyroiditis). Therefore, accurate interpretation of the uptake scan is critical for the correct treatment and differential interpretation will lead to different treatment. We aim to identify inter-individual agreement for interpretation of the thyroid radionuclide uptake scan.

Method: Three assessors (two senior registrars and one consultant endocrinologist) independently reviewed thyroid uptake scans (n=173) carried out in a single university hospital from Sep 2006 to Aug 2014 for patients with thyrotoxicosis who were negative for TSH receptor antibody. All three assessors graded each scan for three patterns – diffuse update, no uptake and patchy/localised uptake according to published criteria. Inter-assessor agreement was analysed using kappa statistics.

Results: All three assessors were in agreement for 71% (n=123) of the scans. The overall kappa was 0.67 (95% CI 0.62–0.71). The highest agreement was with ‘no uptake’ outcome (kappa 0.86), least with ‘patchy/localised uptake’ outcome (0.62) and with ‘diffuse uptake’ outcome (0.65). In scans that lacked agreement (n=50), assessor one would have offered radioiodine as a first line treatment to 66% (n=33) of patients (pathy/localised uptake), assessor two to 46% and assessor three to 20% of patients.

Conclusion: There is a high overall agreement for the interpretation of thyroid uptake scan but inter-individual variation in one third of uptake scans lead to potentially different treatment for patients with thyrotoxicosis.