Diagnosis of adult growth hormone deficiency: still a matter of debate

Primary hyperparathyroidism is associated with marked impairment of GH response to acylated ghrelin

BACKGROUND

Impaired GH secretion is a common finding in patients with primary hyperparathyroidism (PHP). Ghrelin displays strong GH-releasing action, mainly at the hypothalamic level.

OBJECTIVE

To evaluate secretory response of GH to ghrelin in PHP patients.

PATIENTS

Fifteen patients [11 women/4 men, mean age 54 years, range 32-70 years, body mass index (BMI) 25.0 +/- 0.7 kg/m(2)] affected with PHP due to single parathyroid adenoma and 35 normal age-matched subjects (23 women/12 men, mean age 58 years, range 35-68 years, BMI 24.1 +/- 1.1 kg/m(2)).

METHODS

A measure of 1 microg/kg body weight i.v. acylated ghrelin or 1 microg/kg body weight i.v. GH releasing hormone (GHRH) followed by 0.5 g/kg body weight i.v. arginine (ARG) hydrochloride were administered to all subjects on alternate days in order to evaluate GH response.

RESULTS

Mean serum GH peak after GHRH + ARG was 32.6 +/- 7.8 and 17.4 +/- 4.0 microg/l, in controls and PHP patients, respectively (P < 0.05). Mean serum GH peak after ghrelin was 70.4 +/- 31.5 and 16.8 +/- 1.9 microg/l, in controls and PHP patients, respectively, (P < 0.001). Using ROC curves, a serum GH peak > 22 microg/l after ghrelin stimulation might be considered as a cut-off value for identifying normal subjects. Ten (67%) PHP patients have impaired GH response to GHRH + ARG and 13 (87%) to ghrelin. Serum GH peak after ghrelin or GHRH + ARG was unrelated to serum IGF-1, PTH or ionized calcium concentrations.

CONCLUSIONS

The present data confirm that GH secretion is impaired in PHP patients using the potent GH secretagogue ghrelin and suggest that impaired GH secretion is likely due to a deleterious effect of hypercalcaemia at the hypothalamic level in PHP patients.

Growth hormone deficiency (GHD) in adult thalassaemic patients

BACKGROUND AND OBJECTIVE

Short stature and growth hormone deficiency (GHD) are frequent occurrences in thalassaemic children, while data on the prevalence of GHD in adult patients are lacking. Therefore, we elected to study the growth hormone and insulin-like growth factor-I (GH-IGF-I) axis in a large group of adult thalassaemic subjects.

DESIGN

Cross-sectional study on the prevalence of GHD in 94 adult thalassaemic patients (69 with thalassaemia major and 25 with thalassaemia intermedia, 39 men and 55 women, aged 31.5 +/- 6.8 years, on sex steroid replacement when necessary).

METHODS

All patients underwent GHRH (1 microg/kg as an i.v. bolus) plus arginine (0.5 g/kg as a 30 min i.v. infusion) testing. Severe GHD was defined by GH peaks lower than 9 microg/l, whereas partial GHD was defined by GH peaks ranging from 9-16.5 microg/l. Blood samples for IGF-I, ferritin and pseudocholinesterase measurements were collected. Urinary free cortisol (UFC) levels were also assayed.

RESULTS

Severe GHD was demonstrated in 21 of the 94 patients (22.3%), while 18 additional patients (19.1%) displayed partial GHD. GH peaks were positively correlated with IGF-I standard deviation score (SDS) (r = 0.22, P < 0.05), although 1 of the 21 patients with severe GHD showed normal IGF-I SDS values, and 44 of the 55 patients with normal GH reserve displayed low IGF-I SDS. A strong positive correlation (r = 0.48, P < 0.0001) between IGF-I SDS and pseudocholinesterase was identified. No correlations were found between ferritin and UFC levels on the one hand and GH peaks and IGF-I SDS on the other.

CONCLUSION

Findings from this study demonstrate that GHD, either partial or severe, is not a rare occurrence in adult thalassaemic patients. GHD is associated with a higher prevalence of low serum IGF-I levels, recorded also in patients with normal GH secretion. The lack of correlation between ferritin and both GH peaks and IGF-I SDS suggests that mechanisms additional to iron overload, whose relevance cannot however be definitely ruled out, play a role in the pathophysiology of somatotrophin-somatomedin deficiency in this clinical condition. The positive correlation between IGF-I SDS on the one hand and GH peaks and pseudocholinesterase values on the other hand indicates that reduced liver protidosynthetic activity, in addition to somatotrophin secretory status, is a major determinant of the impaired IGF-I production in thalassaemia. Therefore biosynthetic GH replacement therapy in GH-deficient thalassaemic adults is worth considering.

Growth hormone levels in the diagnosis of growth hormone deficiency in adulthood

Current guidelines for the diagnosis of adult growth hormone deficiency (GHD) state that the diagnosis must be proven biochemically by provocative testing that is done within the appropriate clinical context. The need for reliance on provocative testing is based on evidence that the evaluation of spontaneous growth hormone (GH) secretion over 24 h and the measurement of IGF-I and IGFBP-3 levels do not distinguish between normal and GHD subjects. Regarding IGF-I, it has been demonstrated that very low levels in patients highly suspected for GHD (i.e., patients with childhood-onset, severe GHD, or with multiple hypopituitarism acquired in adulthood) may be considered definitive evidence for severe GHD obviating the need for provocative tests. However, normal IGF-I levels do not rule out severe GHD and therefore adults suspected for GHD and with normal IGF-I levels must undergo a provocative test of GH secretion. The insulin tolerance test (ITT) is the test of choice, with severe GHD being defined by a GH peak less than 3 microg/l, the cut-off that distinguishes normal from GHD adults. The ITT is contraindicated in the presence of ischemic heart disease, seizure disorders, and in the elderly. Other tests are as reliable as the ITT, provided they are used with appropriate cut-off limits. Glucagon stimulation, a classical test, and especially new maximal tests such as GHRH in combination with arginine or GHS (i.e., GHRP-6) have well-defined cut-off limits, are reproducible, are independent of age and gender, and are able to distinguish between normal and GHD subjects. The confounding effect of overweight or obesity on the interpretation of the GH response to provocative tests needs to be considered as the somatotropic response to all stimuli is negatively correlated with body mass index. Appropriate cut-offs for lean, overweight, and obese subjects must be used in order to avoid false-positive diagnoses of severe GHD in obese adults.