Clinical usefulness of thyroid ultrasonography in patients with primary hypothyroidism

Chronic thyroiditis (CT) is the main cause of primary hypothyroidism.1, 2, 3 It is usually diagnosed with clinical and hormonal data and mainly based on detecting antithyroid antibodies in the serum. Since the serological study can be falsely negative in at least a quarter of cases,4, 5 the aetiological diagnosis of hypothyroidism is not correctly made in this group of patients. On the other hand, studies show that thyroid ultrasound can reveal CT in up to 34% of patients with a negative serological study with histologically proven CT.3, 4, 5, 6 Therefore, in patients with primary hypothyroidism, the rate of correct aetiological diagnoses may increase when thyroid ultrasound assessment is added to the clinical and serological study.

Establishing the aetiological diagnosis of hypothyroidism is of interest since it allows other causes to be excluded, its natural progression to be foreseen, and the associated comorbidity to be known. It is well known that the progression of hypothyroidism is faster in patients with CT,3, 7 and especially in pregnant women with CT, who, regardless of hypothyroidism, have a higher risk of miscarriage and premature birth,8, 9 and therefore are patients who need closer monitoring and earlier hormone replacement therapy.8 On the other hand, some studies have shown a higher incidence of cancer associated with CT, lymphoma and papillary carcinoma, which appear as thyroid nodules with the typical ultrasound characteristics of malignant thyroid nodules.1, 10

Although in most patients with hypothyroidism, it is not recommended to start hormone replacement therapy until thyrotropin does not exceed 10 mIU/L,7 some conditions can modify this procedure. Among them, nodular goitre may make it advisable to start treatment earlier.3 Some studies have shown a reduction in post-surgical recurrences of nodular goitre in patients receiving hormone replacement therapy,11, 12 others have confirmed a reduction in the volume of the nodules and a lower rate of appearance of new thyroid nodules when managing to maintain normal or subnormal thyrotropin values with levothyroxine-based treatment,13, 14, 15, 16, 17 and other studies have reported a reduction in the incidence of papillary thyroid carcinoma in CT patients treated with levothyroxine,18 all of which demonstrates the influence of thyrotropin levels on the development and growth of thyroid nodules. Thyroid ultrasound in patients with hypothyroidism could be useful to detect coexisting nodular goitre, which, although clinically silent, could motivate the indication to start hormone replacement therapy even if the thyrotropin level is not higher than 10 mU/L.

Despite the performance of ultrasound in the diagnosis of CT and in the diagnosis and characterisation of nodular goitre, this examination is not usually indicated in patients with primary hypothyroidism unless a glandular abnormality or a palpable thyroid mass is clinically observed.5, 19 This is probably due to the underlying idea that hypothyroidism is a functional disorder and that ultrasound is useful for evaluating structural alterations. Therefore, the indication of thyroid ultrasound in patients presenting with primary hypothyroidism may be a topic of interest.

The objective of the study is to evaluate the clinical utility of thyroid ultrasound in patients with primary hypothyroidism without clinical suspicion of nodular goitre. Specifically, to analyse its performance in the aetiological diagnosis of hypothyroidism while evaluating its contribution to the detection and characterisation of coexisting subclinical thyroid nodular pathology.

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