Suppression of growth hormone by oral glucose in the evaluation of tall stature

Prognostic value of nadir GH levels for long-term biochemical remission or recurrence in surgically treated acromegaly

CONTEXT

Outcome of acromegaly surgery is assessed by IGF-1 and glucose-suppressed GH, but whether the latter provides additional clinically relevant information when IGF-1 is normal is unclear. The role of GH suppression testing after surgery requires clarification.

METHODS

We studied 97 acromegaly patients with normal IGF-1 after surgery by measuring GH after oral glucose longitudinally, initially at ≥ 3 months after surgery and repeated one or more times ≥ 1 year later. Nadir GH was categorized as normal or abnormal relative to the 97.5th percentile of nadir GH in 100 healthy subjects, which were ≤ 0.14 µg/L (DSL IRMA) or ≤ 0.15 µg/L(IDS iSYS). Signs and symptoms scores and insulin resistance were followed longitudinally.

RESULTS

Of 68 patients with initial normal GH suppression 63 (93%) remained in remission and of 29 with initial abnormal GH suppression, 9 (31%) recurred. Recurrence was more common in patients with abnormal suppression (P < 0.001). A total of 14 patients recurred, including 5 with normal GH suppression progressing to abnormal and then recurrence. Overall, serial signs and symptoms and insulin resistance assessments did not identify patients with abnormal suppression or recurrence.

CONCLUSION

Risk of recurrence after surgery is increased for patients with a normal IGF-1 level, but abnormal GH suppression. We newly find, using both our and others' cut-offs, that while normal suppression predicts long-term remission in most patients, some can progress from normal to abnormal suppression and then recurrence after many years of follow up. Nadir GH levels are of prognostic value in acromegaly patients with normal IGF-1 levels after surgery.

Reversible Growth Hormone Excess in Two Girls with Neurofibromatosis Type 1 and Optic Pathway Glioma

BACKGROUND

A total of 12 children with neurofibromatosis type 1 (NF-1) with optic pathway glioma (OPG) and growth hormone (GH) excess are reported to date, but no data exist on the long-term outcome. We describe 2 girls with NF-1 with OPG and GH excess treated with somatostatin analogue (SSa) who maintained a normal GH axis after stopping SSa therapy.

METHODS

The diagnosis of GH excess was established from auxological data, persistently high levels of insulin-like growth factor 1 (IGF-1) and a lack of GH suppression during an oral glucose tolerance test.

RESULTS

Both patients were started on SSa treatment. During treatment, growth deceleration and normal IGF-1 levels were documented. The first case stopped treatment following the development of SSa side effects. The second case interrupted SSa when, closed to her final height, a normal IGF-1 level was documented. While off treatment, both cases maintained normal IGF-1 levels and appropriate growth velocity for their age and development, with normal GH secretion on biochemical testing. Both cases received treatment for central precocious puberty.

CONCLUSION

GH excess in NF-1 children with OPG can be reversed and only short-term SSa therapy may be required. The aetiology remains undetermined, but the course suggests a hypothalamic dysfunction.

Investigation and management of tall stature

Referral for an assessment of tall stature is much less common than for short stature. Although the commonest cause is an underlying familial tendency to tallness, there are important disorders that should be considered at the initial assessment. Distinguishing these conditions from normal variations of growth is the key objective when managing the child and family. In some children, further targeted investigations will be needed and in rare instances intervention to limit final height may be appropriate. This article discusses a structured approach to the assessment and management of a child with tall stature.

Current concepts in the biochemical assessment of the patient with acromegaly

Biochemical assessment of a patient for acromegaly aims to definitively establish or exclude the presence of growth hormone excess. Whether applied to a newly recognized patient or to detect residual disease after therapy, this assessment is best accomplished by measurement of both the degree of GH suppression after oral glucose administration (OGTT) and levels of the GH dependent peptide, insulin-like growth factor I (IGF-I). When measured properly and compared to a well-characterized, age-adjusted normative database, elevation of the serum IGF-I level is a sensitive and specific indicator for the presence of acromegaly or persistent disease after therapy. The diagnosis of acromegaly can be confirmed by documenting an elevated IGF-I level in combination with failure of GH to suppress after oral glucose to below 0.3 microg/l, when GH is measured with a highly sensitive and specific assay. Persistently, normal IGF-I levels along with a nadir GH <0.3 microg/l should exclude the diagnosis. In assessing disease status during or after treatment, normalization of IGF-I is an essential criterion for biochemical control. It is important to recognize that nadir GH levels are >0.3 microg/l in some healthy subjects, so this criterion alone is not diagnostic of acromegaly. Also, because of heterogeneity of clinically available GH assays, this GH criterion, which was developed with a research assay, may not be applicable to use with all other assays. A nadir GH cut off of 1 microg/l has been found to be reliable for use with some standard immunoassays. It is recommended that glucose-suppressed GH levels be interpreted in conjunction with those of IGF-I and with consideration of conditions other than acromegaly that can alter them. With greater assay standardization and the use of IGF-I levels along with new rigorous criteria for interpretation of GH suppression during a OGTT we can improve our identification of patients with acromegaly in earlier stages of the disease as well as better recognize residual disease during therapy.

Overgrowth

The predominant influences on fetal growth are maternal and placental factors. Post-natal growth is regulated by a complex interaction between genetic, environmental and hormonal influences. The role of the growth hormone insulin-like growth factor (GH-IGF) system is explored, including the emerging role of IGF-2 in fetal growth. Increasing understanding of the genetics of overgrowth and short stature syndromes is contributing greatly to basic understanding of growth regulation. A range of prenatal overgrowth syndromes is discussed, including those associated with neonatal hyperinsulinism and hypoglycaemia.Post-natal overgrowth may be caused by a diverse range of normal variant conditions, endocrine disorders, chromosomal abnormalities and other genetic syndromes. An approach to diagnosis is presented and major conditions discussed in detail. Sex-steroid therapy for height limitation continues to be a controversial area with uncertainty about height prediction, benefits achieved and possible long-term side-effects.