Growth hormone effects on cortical bone dimensions in young adults with childhood-onset growth hormone deficiency

This was part of a randomised, controlled, open-label study conducted at 22 sites in 12 countries (Australia, Belgium, France, Germany, Hungary, New Zealand, Norway, Poland, Spain, Sweden, Switzerland, UK) [13]. The primary objective of the study was to evaluate the effect of 24 months of GH treatment in young adults with CO GHD on bone mineral density (BMD) in the lumbar spine and hip using dual energy X-ray absorptiometry. In the same study, hand x-rays were obtained to evaluate changes in cortical bone dimensions, as assessed by DXR, during GH treatment. The study was conducted in accordance with Good Clinical Practice guidelines and the Declaration of Helsinki and with approval from appropriate ethical review boards for each study centre.

Young adults (18–25 years; body mass index, BMI, 18–30 kg/m²) diagnosed with CO GHD, on the basis of at least one stimulated test of GH secretion, were included in the trial. All subjects had received GH treatment during childhood until adult height was attained. Subjects with isolated or only two (including GH) pituitary hormone deficiencies were required to undergo a further provocative GH test after their 16th birthday to confirm the diagnosis. The required replacement therapy apart from GH was performed at the discretion of the single investigator. Subjects with three or more pituitary hormone deficiencies were exempt from further testing. GH testing was carried out according to current consensus guidelines at the time of patient recruitment [14]. Patients were excluded from the study if they had received GH treatment during the month prior to randomisation, but information in the single individual on the time since GH was discontinued was not available. Other reasons for exclusion were serious cardiac, hepatic or renal disease, uncontrolled hypertension, diabetes, acromegaly, diseases that could affect bone metabolism or any malignant tumour. Female subjects were excluded if pregnant or lactating. For subjects with more than one (other than GH) known deficient hypothalamic–pituitary axis, replacement doses of thyroid, adrenal, gonadal and/or antidiuretic hormone were to have been unchanged for at least 6 months prior to attendance at the screening visit. There were no significant differences between the treatment and control groups regarding use of pituitary substitution therapy [13].

Patients were randomised (2:1) to either two years' open-label treatment with GH (Norditropin® SimpleXx®, Novo Nordisk, Copenhagen, Denmark) or to an untreated control group. GH was initiated at a starting dose of 0.2 mg/day (males) and 0.4 mg/day (females). The dose was increased to 0.6 and 0.9 mg/day at 1 month and raised again to 1.0 and 1.4 mg/day at 3 months, for males and females, respectively, for the remainder of the study. The higher GH dose was given to females since they require higher doses than males to achieve normal insulin-like growth factor-1 levels [15]. Dose reduction due to GH-related side effects was allowed at the discretion of the investigator. A single daily subcutaneous injection of GH was administered at bedtime using a cartridge pen (NordiPen®, Novo Nordisk, Copenhagen, Denmark). Patients in the control group received no treatment during the study. The trial was conducted as an open-label study and not placebo controlled, since it was deemed unethical to subject young adults to daily placebo injections for 24 months. Each patient attended the clinic at the screening visit (1–5 weeks before randomisation), the randomisation visit, and at 1, 3, 6, 12, 18 and 24 months. The study did not include any information on dietary intake prior to treatment, and there were no specific dietary requirements for the duration of the study.

Radiographs were obtained at months 0, 6, 12, 18 and 24. DXR analysis (Sectra Imtec AB, Linkoping, Sweden) requires a plain or digital radiograph of the non-dominant hand [16]. In this study, plain radiographs were used and sent to a central, blinded reading facility (The Osteoporosis Unit, Hvidovre University Hospital, Copenhagen, Denmark). In order to secure standardised x-rays, a radiographic manual was delivered to all centres, describing positioning of the hand and forearm, film type, a film/focus distance of 100 cm, and the use of 50 kV and 4–8 mAs as exposure parameters. The radiographs were captured as digital images using a flat-bed scanner (600 × 600 dpi, 12-bit greyscale) and three regions of interest (metacarpals 2, 3 and 4) were automatically identified. In each of the three regions, the bone width and inner diameter were measured symmetrically around the centre of the metacarpals at a resolution of 117 lines/cm; the length ‘L’ is 1.5 cm for metacarpal 4—1.8 cm for metacarpal 2 (Fig. 1). Bone width, endosteal diameter, cortical thickness, metacarpal index (MCI) and the areal cross-sectional moment of inertia (CSMI) \( \left( {{\text{CSMI}} = \pi \times \left[ {{{\left( {{\text{bone}}\;{\text{width}}} \right)}^{{4}}} - {{\left( {{\text{inner}}\;{\text{diameter}}} \right)}^{{4}}}} \right]/{64}} \right) \) were then calculated. The latter was included as a geometric indicator of bone strength. The short-term precision of DXR has previously been determined in 40 pre- and postmenopausal women, demonstrating a coefficient of variance (CV) value of 0.65% [17].

Primary analysis of the treatment effect was performed with an ANCOVA model including correction for baseline level and the treatment effect on the logarithmic transformed changes from baseline.

Analyses of the influence of gender, height, weight and BMI were made by including them one by one in a repeated measurement ANCOVA model with treatment, visit, interaction between treatment and visit and baseline level as fixed effects and subject as a random effect. The correlations between radiogrammetric and densitometric measurements were estimated in simple linear regression models.