Elevated IGF-1 with GH suppression after an oral glucose overload: incipient acromegaly or false-positive IGF-1?

To report the evolution of patients with a suggestive clinical scenario and elevated serum insulin-like growth factor-1 (IGF-1), but growth hormone (GH) suppression in the oral glucose tolerance test (OGTT), in whom acromegaly was not initially excluded.

Forty six patients with a suggestive clinical scenario, who had elevated IGF-1 (outside puberty and pregnancy) in two measurements, but GH < 0.4 µg/L in the OGTT, were selected. Five years after initial evaluation, the patients were submitted to clinical and laboratory (serum IGF-1) reassessment. Patients with persistently elevated IGF-1 were submitted to a new GH suppression test and magnetic resonance imaging (MRI) of the pituitary.

Four patients were lost to follow-up. During reassessment, 42 patients continued to show no "typical phenotype" or changes in physiognomy. Fifteen of the 42 patients had normal IGF-1. Among the 27 patients with persistently elevated IGF-1 and who were submitted to a new OGTT, GH suppression was confirmed in all. Two patients exhibited a lesion suggestive of microadenoma on pituitary MRI. In our interpretation of the results, acromegaly was ruled out in 40 patients and considered "possible" in only 2.

Our results show that even in patients with a suggestive clinical scenario and elevated IGF-1, confirmed in a second measurement and without apparent cause, acromegaly is very unlikely in the case of GH suppression in the OGTT.