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Abstract(s)
Introdução: O hipotiroidismo é uma patologia frequente, que afecta cerca de 5% da
população com idade superior a 60 anos. A glândula tiróide normal segrega a totalidade da
tiroxina e apenas 20% da triiodotironina. Os restantes 80% da triiodotironina são obtidos por
desiodação da tiroxina nos tecidos extra-tiroideus. Nem todos os tecidos que necessitam de
hormonas tiroideias são igualmente capazes de converter tiroxina em triiodotironina, a forma
activa da hormona, apresentando taxas de conversão diferentes entre si. Contudo, a maioria
dos pacientes com hipotiroidismo é tratada apenas com levotiroxina. Apesar de este
tratamento ser eficaz na maioria dos indivíduos, cerca de 10% não se sente inteiramente bem.
Este facto está de acordo com o comprometimento da função cognitiva, piores desempenhos
a nível de aprendizagem, memória, atenção, velocidade motora e cognitiva em indivíduos
tratados com tiroxina em monoterapia, comparativamente a uma população de referência. A
terapia de substituição apenas levotiroxina não reproduz com precisão as taxas de produção
tiroideia nem as concentrações séricas de triiodotironina e tiroxina de indivíduos saudáveis.
Tendo em conta todos estes aspectos, tem sido sugerida a utilização da combinação
tiroxina/triiodotironina no tratamento desta patologia.
Metodologia: A presente dissertação propõe-se a comparar a combinação
tiroxina/triiodotironina com a tiroxina em monoterapia no tratamento do hipotiroidismo,
através da revisão e análise da literatura científica mais relevante, publicada até à data, com
recurso ao motor de busca da PubMed e a diversas publicações de organizações reconhecidas
na área da Endocrinologia.
Resultados: Foram identificados no total treze artigos originais e três meta-análises. Os
resultados e os parâmetros analisados divergiram, mas a maior parte dos estudos publicados
não demonstrou um efeito benéfico da combinação tiroxina/triiodotironina relativamente à
monoterapia com tiroxina na maioria dos indivíduos com esta patologia. Apenas dois estudos
encontraram um benefício significativo da terapia combinada, mas foi posteriormente
sugerido que este estaria associado com a causa do hipotiroidismo ou com o efeito placebo.
Discussão e Conclusões: Com base nos resultados obtidos, a monoterapia com tiroxina deve
continuar a ser o tratamento padrão do hipotiroidismo. Porém, não é excluída a possibilidade
de que alguns indivíduos possam beneficiar da combinação tiroxina/triiodotironina,
nomeadamente os portadores de alguns polimorfismos genéticos. É ainda de salientar que a
maioria dos pacientes estudados preferiu a combinação tiroxina/triiodotironina. Os estudos
apresentaram inúmeras limitações, que contribuíram para a variabilidade e alteração dos
resultados. São necessárias futuras pesquisas, mais robustas e que minimizem os factores de
enviesamento, para clarificar esta importante questão.
Introduction: Hypothyroidism is a common condition, which affects about 5% of the population aged over 60 years. Normal thyroid gland secretes all the thyroxine and only 20% of the triiodothyronine. The remaining 80% of triiodothyronine is obtained by thyroxine deiodation in extra-thyroidal tissues. Not all tissues in need of thyroid hormones are equaly able to convert thyroxine in triiodothyronine, the active form of the hormone, with different rates of conversion between them. However, most patients with hypothyroidism are treated only with levothyroxine. Although this treatment is effective in most individuals, about 10% do not feel totally well. This is in agreement with impaired cognitive function, worse results in learning memory tests, attention, cognitive and motor speed in patients treated with thyroxine monotherapy, compared with a reference population. Replacement therapy only with thyroxine does not reproduce physiological thyroid production rates nor serum concentrations of triiodothyronine and thyroxine of healthy individuals. Considering all these facts, the use of combined thyroxine/triiodothyronine treatment has been suggested in this pathology. Methodology: This study proposes to compare combined thyroxine/triiodothyronine treatment with thyroxine monotherapy in hypothyroidism, by reviewing and analysing the most relevant scientific literature published to date, using the PubMed search engine and publications of recognized Endocrinology organizations. Results: Thirteen original articles and three meta-analysis were identified. The results and analysed parameters differ, but most published studies did not demonstrate a beneficial effect of combined thyroxine/triiodothyronine treatment over thyroxine monotherapy in most individuals with this condition. Only two studies found a significant benefit of combined therapy, but it was later suggested that this could be related to the cause of hypothyroidism or the placebo effect. Discussion and Conclusions: Based on the obtained results, monotherapy with thyroxine should remain the standard treatment of hypothyroidism. However, the possibility that some individuals could benefit from combined thyroxine/triiodothyronine treatment, namely those with certain genetic polymorphisms, is not excluded. It should also be noted that most studied patients have preferred the combined thyroxine/triiodothyronine treatment. Studies have had several limitations, which contribute to the variability and changes in results. Further studies, more robust and which minimize the biasing factors, are needed to clarify this important issue.
Introduction: Hypothyroidism is a common condition, which affects about 5% of the population aged over 60 years. Normal thyroid gland secretes all the thyroxine and only 20% of the triiodothyronine. The remaining 80% of triiodothyronine is obtained by thyroxine deiodation in extra-thyroidal tissues. Not all tissues in need of thyroid hormones are equaly able to convert thyroxine in triiodothyronine, the active form of the hormone, with different rates of conversion between them. However, most patients with hypothyroidism are treated only with levothyroxine. Although this treatment is effective in most individuals, about 10% do not feel totally well. This is in agreement with impaired cognitive function, worse results in learning memory tests, attention, cognitive and motor speed in patients treated with thyroxine monotherapy, compared with a reference population. Replacement therapy only with thyroxine does not reproduce physiological thyroid production rates nor serum concentrations of triiodothyronine and thyroxine of healthy individuals. Considering all these facts, the use of combined thyroxine/triiodothyronine treatment has been suggested in this pathology. Methodology: This study proposes to compare combined thyroxine/triiodothyronine treatment with thyroxine monotherapy in hypothyroidism, by reviewing and analysing the most relevant scientific literature published to date, using the PubMed search engine and publications of recognized Endocrinology organizations. Results: Thirteen original articles and three meta-analysis were identified. The results and analysed parameters differ, but most published studies did not demonstrate a beneficial effect of combined thyroxine/triiodothyronine treatment over thyroxine monotherapy in most individuals with this condition. Only two studies found a significant benefit of combined therapy, but it was later suggested that this could be related to the cause of hypothyroidism or the placebo effect. Discussion and Conclusions: Based on the obtained results, monotherapy with thyroxine should remain the standard treatment of hypothyroidism. However, the possibility that some individuals could benefit from combined thyroxine/triiodothyronine treatment, namely those with certain genetic polymorphisms, is not excluded. It should also be noted that most studied patients have preferred the combined thyroxine/triiodothyronine treatment. Studies have had several limitations, which contribute to the variability and changes in results. Further studies, more robust and which minimize the biasing factors, are needed to clarify this important issue.
Description
Keywords
Tiróide Hipotiroidismo - Terapia Tiroxina Triiodotironina
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Universidade da Beira Interior