Subclinical hypothyroidism: a historical view and shifting prevalence

Abstract

Background and Aims: Accurate diagnosis and treatment of subclinical hypothyroidism (SCH) is challenging in clinical practice because of differing upper limits of normal (ULN) for thyroid-stimulating hormone (TSH). This review summarises the various definitions of SCH and their impact on reported SCH prevalence. Methodology: Articles reporting the prevalence of SCH in relation to the ULN of TSH in human studies were identified through an English-language PubMed search for 'subclinical hypothyroidism,' 'prevalence,' and 'TSH' within the title and/or abstract. Relevant articles and related literature were selected for inclusion. Results: Estimates for the prevalence of SCH varied by sex, age, race/ethnicity, and geographic location (range, 0.4-16.9%). Higher rates of SCH were consistently reported in women (0.9-16.9%) and older individuals (2.7-16.9%). However, the ULN of TSH in those considered free of thyroid disease and not at risk increased progressively with age, suggesting that reports of SCH prevalence in elderly people may be overestimated. Multiple studies reported an increased risk of progression to overt hypothyroidism among individuals with elevated TSH and antithyroid antibodies. Conclusions: Given the variable definition of SCH based on an inconsistent ULN for TSH, it is currently difficult to ascertain the true prevalence of SCH and to correctly label and treat patients with SCH; use of age-adjusted definitions may be considered when assessing prevalence. A diagnosis of SCH does not necessarily merit treatment, especially if TSH elevations are transient (i.e. not persistent for > 3-6 months) and the patient lacks other risk factors for developing overt hypothyroidism. Review criteriaStudies were identified through a PubMed search for 'subclinical hypothyroidism' (SCH), 'prevalence,' and 'TSH' (thyroid-stimulating hormone) within the title and/or abstract field. The results were limited to English-language studies in humans. Abstracts were reviewed, and studies reporting the prevalence of SCH in relation to the upper limit of normal for TSH were selected for inclusion, as well as additional relevant articles. Message for the clinicThe true prevalence of SCH is currently difficult to precisely assess, as the current definition of SCH has not been consistently applied in previous studies and does not account for individual patient factors, including the age-adjusted upper limit of normal for TSH, positivity for thyroid antibodies, and racial and ethnic differences. A diagnosis of SCH does not necessarily mean that treatment is merited.

Systemic features of retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations: a monogenic small vessel disease

“…Of interest, hypothyroidism has been reported in 14 patients with Aicardi-Gouti eres syndrome, which can be caused by homozygous missense mutations in TREX1 [25], that is different to the heterozygous C-terminal truncating mutations causing RVCL-S. Subclinical hypothyroidism is also considered a marker of endothelial dysfunction in diabetic retinopathy and chronic kidney disease [26,27]. Subclinical hypothyroidism is a common disorder, with an estimated prevalence of 6% in the general population, which may increase to 17% in the elderly, most prominently in females [28,29]. The prevalence of subclinical hypothyroidism in MCÀ over age 40 is 8% (2/25), and thus comparable to the prevalence in the general population, the prevalence in MC+ over age 40 is markedly increased with 37% (7/19) compared to the general population.…”

Prevalência De Hipotireoidismo Em Pacientes Com Queixas De Distúrbios Respiratórios Relacionados Ao Sono

“…Em relação ao índice da apneia/hipopneia (IAH) os pacientes foram agrupados na seguinte classificação: Normal (IAH < 5 eventos/hora), SAOS leve (IAH de 5 a 15 eventos/ hora), SAOS moderada (IAH de 16 a 30 eventos/hora), SAOS grave (IAH > 30 eventos/hora) (18) . Da mesma forma, em relação ao Índice de Massa Corporal (IMC) os pacientes foram agrupados de acordo com a classificação da OMS: peso ideal (18,(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)9 Kg/m 2 ), sobrepeso (25, O gênero masculino predominou no Grupo com SAOS (71,5%), mas no Grupo sem SAOS houve predomínio do gênero feminino (57,2%), sendo esta diferença estatisticamente significante (p=0,0001). Em ambos os grupos houve maior prevalência de pacientes na faixa etária adulta e, em relação ao IMC, também em ambos os grupos, os pacientes com sobrepeso seguido daqueles com obesidade Grau I foram os mais prevalentes.…”

“…Em adição, esses mesmos pacientes têm uma "melhora temporária" dos sintomas, com os tratamentos preconizados para a SAOS, com inevitável falência desses tratamentos a longo-prazo. Essa "melhora temporária" pode ser evitada se o diagnóstico de hipotireoidismo não for adiado (5,(14)(15) . Este estudo tem como objetivo determinar a prevalência de hipotireoidismo em pacientes com queixas de distúrbios respiratórios relacionados a sono, quando da primeira consulta.…”

Age- and Sex-Specific TSH Upper-Limit Reference Intervals in the General French Population: There Is a Need to Adjust Our Actual Practices

“…A major question deriving from the change of TSH with age is to decide whether or not TSH reference intervals need to be adapted to the most elderly in order to evaluate their thyroid function. This is of importance, as the proportion of patients who will be classified as having subclinical hypothyroidism may greatly differ according to the upper value of the reference interval [8]. Two different approaches exist to define reference intervals: the direct approach is based on the recruitment and selection of control subjects [9], whereas the indirect approach is based on the analysis of available data from routine testing [10].…”