A hypoechoic pattern of the thyroid at ultrasound does not indicate autoimmune thyroid diseases in patients with morbid obesity

Abstract

Objective: Thyroid ultrasound (US) scan is a valuable tool for diagnosing thyroid diseases. In autoimmune thyroid disease (AITD), an hypoechoic pattern of the thyroid at US is related to circulating thyroid antibodies (Abs). The aim of this study was to evaluate the diagnostic accuracy of thyroid US for the detection of AITD in patients with morbid obesity. Design: Thyroid US scans showing an hypoechoic pattern of the thyroid were collected from 105 morbid obese patients (body mass index (BMI) O40 kg/m 2 ) and 105 non-obese patients (BMI%30 kg/m 2 ). Results: A thyroid hypoechoic pattern at US was consistent with clinical/biochemical features of AITD in 90/105 (85.7%) non-obese patients and in 22/105 (20.9%) morbid-obese patients (P!0.0001). By performing a complete thyroid work-up, including clinical examination, thyroid morphology, serum hormones, and auto-Ab measurements, the discrepancy between the US pattern and the results of the thyroid Ab tests was justified in 6/15 non-obese patients, and only in 1/83 morbid obese patients. Thus, an unexplained hypoechoic pattern of the thyroid at US, defined as negative tests for thyroid Ab and absence of justifying thyroid disturbances, was found in 2/105 (1.9%) non-obese patients and in 68/105 (64.8%) morbid obese patients (P!0.0001). Conclusions: Our results suggest that i) morbid obesity may affect thyroid morphology, and ii) an hypoechoic pattern of the thyroid at US, a well-established parameter for diagnosing AITD, has a poor diagnostic accuracy when patients with morbid obesity are taken into account.

Prevalence of goiter and thyroid nodular disease in patients with class III obesity

“…Chiovatto and cols. also evaluated the accuracy of US in detecting autoimmune thyroid diseases in patients with class III obesity, and detected that class III obesity may affect thyroid morphology (8).…”

“…Additionally, the prevalence of more severe forms of obesity, defined as class III obesity, has been increasing worldwide (1). Over recent years, various publications have focused on the association between insulin resistance (IR) and thyroid abnormalities (2)(3)(4)(5)(6)(7)(8). Causes of thyroid dysfunction are positively associated with IR, not only in subjects diagnosed with diabetes mellitus (DM), but also in subjects without this diagnosis (9).…”

MECHANISMS IN ENDOCRINOLOGY: The crosstalk between thyroid gland and adipose tissue: signal integration in health and disease

“…After weight loss, a reduction in thyroid volume was also observed (60). Studies on children and adults also demonstrated that obesity is associated with a thyroid hypo-echogenic pattern at US, which occurs independently from thyroid autoimmunity (77,78). Indeed, among all patients with a thyroid hypo-echogenic pattern of the gland, only a minority of those with morbid obesity (20%) had serological evidence of thyroid autoimmunity (78).…”

“…Studies on children and adults also demonstrated that obesity is associated with a thyroid hypo-echogenic pattern at US, which occurs independently from thyroid autoimmunity (77,78). Indeed, among all patients with a thyroid hypo-echogenic pattern of the gland, only a minority of those with morbid obesity (20%) had serological evidence of thyroid autoimmunity (78). This figure was in contrast with the much greater prevalence (O80%) of thyroid antibodies in non-obese patients.…”

Serum negative autoimmune thyroiditis displays a milder clinical picture compared with classic Hashimoto's thyroiditis

“…However, these early studies enrolling patients with raised serum levels of TSH did not take into account the presence of clinical conditions associated with an increase in circulating TSH levels recently proven not to be indicative of thyroid failure. In particular, morbid obesity has recently been identified to cause an increase in the serum levels of TSH often associated with the presence of a hypoechoic pattern of the thyroid at US, which do not imply that hypothyroidism is present (24,25,26,27). Taking into account the above concepts, it would be reasonable to assume that the prevalence of SN-CAT might have been overestimated by earlier studies.…”