TSH measurement is not an appropriate screening test for autonomous functioning thyroid nodules: a retrospective study of 368 patients

Abstract

Objective: Based on the assumption that normal TSH concentration rules out the presence of autonomous functioning thyroid nodules (AFTNs), clinical guidelines on the management of thyroid nodules only recommend a thyroid scan if TSH concentration is subnormal. However, the proportion of AFTN presenting with a normal TSH is unknown. Our objective is therefore to determine the proportion of AFTNs with a normal TSH level to ascertain whether a normal TSH really rules out an AFTN. Design: Retrospective study on 368 patients with an AFTN. Methods: Thyroid scans with a diagnosis of AFTN were reviewed retrospectively by one of us (R Moreno-Reyes), blinded to the clinical data. The diagnosis of solitary AFTN was confirmed in 368 patients. Among them, we selected 217 patients based on the absence of another thyroid nodule O10 mm, the absence of medical conditions able to interfere with thyroid function, and the completeness of the data. Results: The proportion of AFTNs with normal TSH was 49%. This proportion increased to 71% in patients for whom thyroid scan was performed in the workup of a thyroid nodule. Conclusions: Our data suggest that serum TSH is not an effective screening tool to diagnose AFTNs. Using 'TSH-only' screening, as recommended by the majority of guidelines, the diagnosis of AFTN would have been missed in 71% of our patients in the workup of a thyroid nodule. Thyroid scan remains the gold standard for detecting AFTN and should be considered before performing fine-needle aspiration cytology (FNAC), as the reliability of FNAC in an unsuspected AFTN remains unclear.

Prevalence of normal TSH value among patients with autonomously functioning thyroid nodule

“…Accordingly, comparative studies proved substantial equivalence of 99m Tc-pertechnetate and radioiodine in clinical practice [1,2,36,37]. Third, criteria adopted to exclude from TS patients with potential interferences on thyroid function were detailed in three of selected papers [23,25,27]. Anyway, even if such criteria were not stated in remaining papers, scrutiny for interferences is a standard of care in nuclear medicine.…”

“…The full text of six eligible articles was retrieved and two additional studies were found screening the references of the selected articles. Finally, eight articles including series of patients with AFTN were selected for the meta-analysis [16,[21][22][23][24][25][26][27] (Fig. 1).…”

“…Concerning the geographic distribution, studies from Europe, Asia and America were included. AFTN was defined as a focal increased uptake on TS corresponding to a thyroid nodule larger than 10 mm detected by thyroid ultrasound (US) in six papers [21,[23][24][25][26][27], to a palpable nodule in one study [16] and to a palpable nodule confirmed by thyroid US in the remaining one [22]. Most of the studies enrolled patients in whom TS was performed using 99m Tc-pertechnetate as radiopharmaceutical while both 99m Tcpertechnetate and 123 I were employed by Iwata et al [21] and…”

“…Criteria adopted to exclude from TS patients who were exposed to iodine, interfering drugs or affected by interfering medical conditions were detailed in three of selected papers [23,25,27]. A total of 2761 patients with AFTN detected by TS were available for our pooled analysis.…”

Why the European Association of Nuclear Medicine has declined to endorse the 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer

“…Furthermore, the EANM believes that thyroid scintigraphy still has its place in the diagnostic workup of nodular thyroid disease, especially in regions, including a number of EANM member countries, with a known or recently alleviated iodine deficiency. In such populations a normal TSH level cannot rule out thyroid autonomy [8][9][10][11]. In their retrospective study, Chami et al [9] found that 49 % of patients with an autonomously functioning focal thyroid nodule had a normal TSH level.…”