Endocrine Abstracts (2018) 56 S3.2 | DOI: 10.1530/endoabs.56.S3.2

Subclinical hypothyroidism is 'not' a disease (Contra)

Laura Gathercole


UK.


Thyroid diseases are common disorders. Globally, hypothyroidism is still frequently caused by iodine deficiency. In iodine sufficient areas, the most common cause of hypothyroidism is thyroid autoimmunity. Subclinical hypothyroidism is defined as elevated thyroid-stimulating hormone (TSH) levels with free thyroxine (fT4) estimates within the reference range. It is a common disorder that increases with age affecting up to 20% of the elderly, with a higher prevalence in women. Some prospective data have shown increased risks of coronary heart disease, heart failure, and cardiovascular mortality among affected adults, while others have not. Conflicting results have further been found on the association between subclinical hypothyroidism and cognitive impairment, depression and the risk of fractures. Overt hypothyroidism must be treated with levothyroxine. It is less clear if subclinical hypothyroidism requires replacement therapy. Screening for thyroid disease is not recommended by guidelines, but case finding based on specific criteria form general practice among endocrinologists. Since the condition is solely based on a laboratory diagnosis, there are many difficult factors to be aware of, including definition of the reference ranges for TSH and T4, both of which depend on laboratory and population factors; how measurements and interpretations of the laboratory tests for thyroid related hormones may be complicated by confounders due to medications, oral contraceptives, other diseases, non-thyroidal illness, and interference, and the difficulty of laboratory measurements to correct for these changes. Furthermore, the few randomized clinical trials have shown no beneficial effect from T4 treatment. Thus, due to current lack of evidence regarding the optimal treatment strategy in individuals with subclinical hypothyroidism, the best management of such persons is inclusion in trials, or to follow serum TSH values, which often normalize spontaneously. If TSH levels exceed 10 mIU/l, substitution might be considered, but even then, there is no direct evidence justifying treatment.

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