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

Abstract

Objective: 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. Subjects and methods: 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. Results: 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. Conclusion: 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. Arch Endocrinol Metab. 2016;60(6):510-4

The Biochemical Diagnosis of Acromegaly

“…Imaging revealed a potential pituitary microadenoma in 2 patients, and acromegaly was ruled out in 40 patients. These findings suggest that acromegaly is very unlikely in patients with suppressed GH after glycemic load [32].…”

Discordant parameters of insulin-like growth factor 1 and growth hormone in the diagnosis and monitoring of acromegaly

“…Calsolari в течение 5 лет наблюдали пациентов с немного увеличенным уровнем ИФР-1 и достаточным подавлением СТГ в ходе ОГТТ, ни у одного из 42 пациентов не развилась акромегалия. Это позволило авторам утверждать, что снижение СТГ в ходе ОГТТ надежно исключает акромегалию [26].…”

Diagnosis of acromegaly: black, white… and sometimes gray!

“…This means that 2.5% of the normal healthy population may have IGF-I levels above the ULN. All these factors may explain why some of the subjects reported in the article by Rosario and Calsolari were found to have elevated IGF-I levels despite perfectly normal GH secretion (10). The fact that IGF-I levels were above the ULN not only at the first sampling but also at the subsequent measurement five years later suggests that IGF-I levels, like other biological parameters such as TSH, tend to be "set" at an individual level which varies very little, within a range narrower than that of the reference population (11).…”