The symptoms of hypogonadism in men with acromegaly are similar to those of men with prolactinomas, including oligospermia and reduced sperm motility. These manifestations, like the specific acromegalic clinical features (see Table 2), progress slowly. Therefore, the diagnosis of acromegaly is often delayed for as many as 5 to 15 yr (22).
The specific clinical manifestations of acromegaly are caused by excessive GH/IGF-1 secretion. In addition, pituitary tumor mass effects (headaches, hypopituitarism, and visual disturbances) are common, because of the high prevalence of macroadenomas (approx 75% of somatotroph adenomas) (22,46).
An elevated random serum GH level is not absolutely necessary for the diagnosis of acromegaly. On the contrary, serum IGF-1 levels are invariably high in acromegaly. If IGF-1 is increased and the random GH level is normal, an oral glucose tolerance test (75 g) is used to establish the diagnosis. A normal response is a decrease in the serum GH level to less than 1 ^g/L, but patients with acromegaly do not suppress normally, and 20% of patients have a paradoxical GH rise (14,47).
After the clinical and endocrine diagnosis of acromegaly is made, radiological evaluation of the pituitary gland should be performed, preferably by MRI with gadolinium enhancement to localize and delineate the tumor from the surrounding tissues. GH-secreting tumors are larger than prolactinomas at the time of the radiographic evaluation, perhaps because of a later clinical presentation (19).
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