Studies on subclinical hypothyroidism with special reference to the serum lipid pattern.

Subclinical hypothyroidism is an example of the impact of technology on the concept of a disease. It denotes a condition in which laboratory findings, at least including a raised serum thyrotropin (s-TSH), indicate hypothyroidism in the absence of clinical signs or symptoms of this disease. One reason for attention to cases of subclinical hypothyroidism is the publication of reports, from the time before introduction of the s-TSH assay, that hypercholesterolaemia precedes other evidence of thyroid failure with attendant risks of ischaemic heart disease and other atherosclerotic manifestations. The present investigation, which concerned the lipid pattern in sublinical hypothyroiism, offered no support for such a concept of hypercholesterolaemia as a premonitory sign of hypothyroidism. Furthermore, no significant differences were found between the serum levels of cholesterol and triglycerides before and after the administration of a thyroxine dose, necessary to suppress the s-TSH into a normal range, in cases of sublinical hypothyroidism. Nor were there any changes during this therapy in body weight, ECG, or Hb levels, which represent important parameters often found to be abnormal in overt hypothyroidism. From a practical point of view, subclinical hypothyroidism probably can be regarded as a state in which reduction of thyroid activity has been compensated by an increased s-TSH secretion to maintain a clinically euthyroid state. When no goitre is found, the rationale of treatment of this condition remains to be proved.