Thyroid size determined by ultrasound. Influence of physiological factors and non-thyroidal disease.

Grading of goitre size according to WHO or the palpatory estimation of thyroid volume does not allow a quantitative estimation of thyroid size or an objective follow-up during treatment with e.g. radioiodine. The present and other studies have demonstrated that the ultrasonic evaluation of thyroid volume is both accurate and precise. In addition, it is non-invasive, rapid, inexpensive and without discomfort to the patient. Using this technique it was demonstrated that thyroid volume increases with increasing age and body weight in both sexes, with weight having the most pronounced influence. The relationship between thyroid volume, body weight and age in non-goitrous healthy subjects can be described using a formula that allows the calculation of normal thyroid size for a population: Thyroid volume (ml) = 1.97 + 0.21 x bodyweight (kg) + 0.06 x age (years). Cigarette smoking is associated with an approximately 10-fold increase in goitre frequency probably due to a combination of an increased sympathetic stimulation of the thyroid and an iodine deficiency state caused by inhalation of thiocyanate. Although no seasonal alteration in serum TSH level could be demonstrated thyroid volume is 23% higher in the winter than in the summer. Cyclic alterations of thyroid volume possibly related to TSH alterations have been found with a 50% difference between minimum values in the first half and maximum values in the second half of the menstrual cycle. Nonthyroidal illnesses are associated with marked alterations in thyroid volume. Thus, chronic renal disease and acute hepatic disease demonstrate significant increases in thyroid volume although the precise mechanisms have not been clarified. Chronic hepatic disease per se and chronic nonrenal nonhepatic disease does not seem to influence thyroid volume. Chronic alcoholism, however, with or without liver cirrhosis is associated with a marked decrease in thyroid volume and an increase in the amount of fibrosis probably related to a direct toxic effect of alcohol on the thyroid. All these factors should be kept in mind when goitre frequency, goitrogenic action of drugs and goitre treatment effects are evaluated.