Clinical Study Safety and Efficacy of Low-Level Laser Therapy in Autoimmune Thyroiditis: Long-Term Follow-Up Study Danilo Bianchini Höfling , 1 Maria Cristina Chavantes, 2 Carlos Alberto Buchpiguel, 3 Giovanni Guido Cerri, 3 Suemi Marui , 4 Paulo Campos Carneiro, 5 and Maria Cristina Chammas 1 1 Ultrasound Unit, Department of Radiology, University of Sao Paulo Medical School, Hospital das Clínicas, 05403-000 São Paulo, SP, Brazil 2 Universidade Nove de Julho, Post-Graduation, 01504-001 São Paulo, SP, Brazil 3 Radiology Institute (InRad); Department of Radiology, University of Sao Paulo Medical School, Hospital das Clínicas, 05403- 000 São Paulo, SP, Brazil 4 Thyroid Unit, Department of Endocrinology and Metabolism, University of Sao Paulo Medical School, Hospital das Clínicas, 05403-000 São Paulo, Brazil 5 Department of Pathology, University of Sao Paulo Medical School, Hospital das Clínicas, 05403-000 São Paulo, Brazil Correspondence should be addressed to Danilo Bianchini Höfling; dbhofling@uol.com.br Received 2 November 2017; Revised 24 June 2018; Accepted 24 July 2018; Published 4 November 2018 Academic Editor: Sabrina Corbetta Copyright © 2018 Danilo Bianchini Höfling et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Introduction. A randomized clinical trial (RCT) was performed to evaluate the efficacy of low-level laser therapy (LLLT) for hypothyroidism induced by chronic autoimmune thyroiditis (CAT). Objective. The objective was to assess the safety and actions of LLLT 6 years after completion of the RCT. Materials and Methods. Forty-three participants were invited to participate in this study 6 years after completion of the RCT. Twenty-five were subjected to LLLT (group L), and 18 were subjected to placebo (group P). Primary outcome measure: frequency of thyroid nodules, which were subjected to fine- needle aspiration biopsy. Secondary outcome measures: dose of levothyroxine required to treat hypothyroidism, thyroid peroxidase antibodies (anti-TPO), and anti-thyroglobulin antibodies (anti-Tg). Results. In group L, a nodule was observed in three patients, who all had a Bethesda II classification. In group P, a nodule was also observed in three patients, with two classified as Bethesda II and one as Bethesda III. The levothyroxine dose required by group L was significantly lower than that required by group P (P =0 002). The anti-TPO and anti-Tg levels did not differ between the groups. Conclusion. LLLT, by the methods described, has been shown to be safe for the treatment of hypothyroidism resulting from CAT. This trial is registered with ClinicalTrials.gov Identifier: NCT02240563. 1. Introduction Low-level laser therapy (LLLT), or photobiomodulation (PBM), is a simple, noninvasive procedure without ionizing radiation in which red or infrared light is used. Its action has already been studied in several tissues, including thyroid tissues. Electron microscopy studies have shown that the use of LLLT does not cause damage to the thyroid parenchyma of mice [1–3]. Furthermore, in rats, LLLT ameliorated the dam- aging effect of gamma irradiation on the gland [4]. In humans, we initially assessed LLLT in patients with hypothyroidism caused by chronic autoimmune thyroiditis (CAT) in a pilot study [5]. We then studied patients under the same conditions using a randomized clinical trial (RCT) [6–8]; the results showed a reduction in the levothyroxine (LT4) doses required to treat hypothyroidism, and 47.8% of Hindawi International Journal of Endocrinology Volume 2018, Article ID 8387530, 9 pages https://doi.org/10.1155/2018/8387530