ECE2018 Debates Subclinical hypothyroidism is a disease (2 abstracts)
Italy.
Primary subclinical hypothyroidism (SH) is commonly defined by laboratory parameters (TSH above the commonly accepted reference range of about 0.44.0 mU/l with normal FT4). This definition does not implies actual thyroid dysfunction, since individual variations of hypothalamic-pituitary feedback set point due to endogenous (genetic, age/gender, NTIS) or exogenous (e.g. drugs) factors may lead to TSH increase in the absence of thyroid disease. Thus, to answer the question of this debate if SH is a disease, the first step is to not consider SH any condition of increased TSH and serum FT4 without a complete clinical evaluation and further laboratory (thyroid autoantibody assay) and instrumental (ultrasound) investigations. Moreover, the term subclinical is somewhat misleading, since symptoms of mild or very mild thyroid failure may be absent or non-specific, with many cases of clinical primary hypothyroidism (increased TSH, low FT4) very difficult to recognize on clinical grounds, especially in the elderly. The term of mild (or very mild) primary hypothyroidism is therefore more appropriate. Thus, when increased TSH is associated with one known cause of thyroid failure (mostly autoimmune thyroiditis, previous thyroid surgery or radiation), there should be no doubt that mild primary hypothyroidism is a (thyroid) disease. A different question is whether this mild disease needs to be treated with levothyroxine (LT4), as clinical/overt hypothyroidism. Arguments in favour to treat mild primary hypothyroidism include the risk of progression to overt thyroid failure, increased cardiovascular risk (dyslipidemia, increased atherosclerosis and ischemic heart disease, hypertension, decreased endothelial function, decreased systolic and diastolic heart function), potential impairment of neuro-psychological fetal development in pregnant women and mood/cognition disorders. Although several short-term intervention studies provide evidence for improvement of several cardiovascular and cognitive parameters, the main argument against treatment is represented by the lack of convincing evidence from prospective controlled trials. However, epidemiological data suggest that mild hypothyroidism may be protective in the elderly. Nevertheless, several retrospective meta-analyses consistently indicate higher cardiovascular risk in subclinical hypothyroid subjects aged <65 yrs, suggesting the need of prospective controlled trials to ascertain whether and to what extent an early therapeutic intervention may be envisaged in younger subjects with mild thyroid failure. In conclusion, if increased serum TSH is the consequence of a primary thyroid pathology, subclinical (mild) hypothyroidism is a disease. The question of whether and when this mild disease deserves treatment is far to be answered.