INTRODUCTION: Chronic autoimmune thyroiditis (TCA) is the main cause of acquired hypothyroidism, which requires continuous treatment with levothyroxine (LT4). A randomized, placebo-controlled trial including 43 patients with hypothyroidism caused by TCA without nodules on ultrasonography study (US) was conducted from March 2006 to March 2009 (NCT01129492). Among them, 23 were submitted to low-level laser therapy (LLLT) and 20 to placebo. The LLLT was effective in improving the echogenicity, the volume and of the thyroid vascularization pattern by US. There was also improvement in the thyroid function and reduction of serum thyroid peroxidase antibodies (TPOAb). Although the results have shown promising and LLLT has shown to be safe in many study models, the long-term LLLT actions on the thyroid parenchyma are unknown. Thus, the objective of this study is to perform biochemical tests and thyroid US six years after the clinical trial interventions to evaluate levothyroxine dose, serum levels of autoantibodies and, especially, the frequency and nature of nodules in the gland and then compare these variables between LLLT and placebo groups. METHODS: This study will include the trial participants performed six years before. The levothyroxine dose and serum levels of thyrotropin (TSH), T3, T4, free T4, TPOAb and anti-thyroglobulin antibodies (TgAb) will be evaluated in these patients. The thyroid US will assess the texture (with particular attention to identifying nodules), echogenicity, volume, as well as vascularization of the gland. The US nodules features, such as dimensions, shape, margins, extracapsular invasion, echogenicity, texture, hypoechoic halo, calcification, internal content, vascularization pattern and resistivity index will be searched. Regional lymph nodes and other characteristics will be also investigated. The USs will be carried out by only one examiner who will be blinded for the previously performed intervention (LILT or placebo). The same investigator will execute a fine needle aspiration (FNA) of patients with thyroid nodules. The cytological analysis of the material collected from the nodules will be undertaken by a pathologist who will be also blinded for the treatment assignments. RESULTS: The following variables will be compared between the two groups: levothyroxine doses, antithyroid antibodies, US parameters, thyroid nodules (if detected) and in this case, the result of their respective FNA.

Inclusion Criteria:

All patients who have hypothyroidism caused by autoimmune thyroiditis included in the randomized, placebo controlled clinical trial (NCT01129492)

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Exclusion Criteria:

All patients who have hypothyroidism caused by autoimmune thyroiditis included in the aforementioned trial (NCT01129492) who underwent surgery and/or therapeutic administration of radioiodine for thyroid diseases during the period between the initial assessment of patients up to the present study.