Body composition and skeletal metabolism following pituitary irradiation in acromegaly.

The change in body composition in acromegaly that resulted from pituitary irradiation was examined using the technic of total body neutron activation analysis. Before treatment, increased ratios of total body P:Ca, P:K and Na:K were noted. After pituitary irradiation, the total body levels of P, Na and K were reduced in a proportion that indicated restoration of body composition towards normal. Skeletal mass (total body calcium) decreased into the range observed in osteoporosis in several patients. Trabecular bone mass, as reflected by the Singh Index, was consistently reduced, and two patients had vertebral compression fractures. Local bone mass as determined by photon absorptiometry was reduced when the values were normalized for age, sex and body size. It is postulated that in untreated acromegaly there is differential bone remodelling with an increase in cortical bone accompanied by a reduced trabecular bone mass. When reduction of hGH levels is accomplished with treatment, cortical apposition may decrease. Since the increased cortical bone mass probably aids in preventing vertebral compression fractures, the treated acromegalic patient may incur an increased risk of fractures. This risk may be increased further by the hypogonadism which may arise secondary to pituitary irradiation or surgery. It would be prudent to ensure that the hypogonadal acromegalic patient receives an adequate calcium intake and sex hormone replacement therapy.