Estudo da integridade das estruturas da via auditiva central de crianças com hipotireoidismo congênito por meio de avaliações eletrofisiológicas: Potenciais evocados auditivos de curta e média latência

Abstract

Hypothyroidism, defined as generalized alterations of metabolic processes caused by the decrease of thyroid function and consequent reduction or lack of hormone production, can be accompanied of serious sequelae in development, that is the reason why newborn screening programs are justified. A direct relation between CongenitalHypothyroidism and the peripheral auditory deficiencies has been established; however, one does not know much about the alterations in the central auditory nervous system in the presence of thyroid dysfunction. It is important to notice that thyroid hormones are essential for the normal cerebral development, being an important regulator of synapses,processes of myelinization, synthesis, and the action of neurotransmitters. Therefore, my main objective was to study the central auditory pathways through the short and middle latency auditory evoked potential in children diagnosed with Congenital Hypothyroidism (CH), under hormone treatment, selected by the State Program of Newborn Screening of Minas Gerais (PETN-MG). Thirty-six children were enrolled in this study: 18 female patients and 18 male patients. They were 8-12-year-old (average age: 10) children with treated CH (Group I), and twenty-nine 8-12-year-old children (average age: 11), 12 female patients and 17 male patients (Group II). They were euthyroid children (showing normal TSH, Free T4) with no autoimmune thyroid diseases (ATPO within normal limits). The first article stressed the short latency auditory evoked potentials (brainstem auditory evoked potentials - BAEP) showingadequate responses, considering the absolute latency values of the waves I, III, and V, the interpeak intervals, and replicability. Significant statistical differences between the two assessed groups have not been found. These findings suggested that in the presence of treated congenital hypothyroidism, the BAEPs behaved in the same way as in thecases of individuals without thyroid diseases, not interfering with the synchronization of the neural firings, which suggests the importance of the adequate control of the hypothyroidism. The second article focused on the characterization of the middle latency auditory evoked responses in order to raise the probability of a hypothesis of the presence of central auditory dysfunction in children with Congenital Hypothyroidism.Significant statistical alterations between the two assessed groups have been found, considering the ear effect (A1C3 x A2C3) and electrode effect (A2C4 x A2C3). In Group I, Na, Pa, and Nb have been detected in 100% of the cases, and Pb has been identified in 77,8%. Latencies remained within normal limits of the reference standard. Only one child with CH was reported with latencies increase and the decrease of response amplitude has also been observed in both groups, however remaining within the 2.5 SD (Standard Deviation), when compared with the reference standard. Such findings suggest that, although being treated, Congenital Hypothyroidism can present manifestations in the central auditory nervous system, particularly in its higher airways. Thus, it is important clinical accompaniment and auditory stimulation.