Treatment of the adult growth hormone deficiency syndrome: Directions for future research

The adult growth hormone deficiency syndrome (AGHD) is a well-defined clinical entity characterized by decreased lean body mass and bone mineral density, increased visceral adiposity, abnormal lipid profile, decreased muscle strength and exercise endurance, and diminished quality of life. Recent studies have emphasized the increased morbidity and mortality of hypopituitary patients, and there are now data implicating growth hormone (GH) deficiency as a cause of this increase. GH replacement therapy has been shown to reverse many of these abnormalities and to be well tolerated. Meta-analyses have demonstrated that GH treatment positively affects cardiovascular risk factors, and controlled trials have shown that visceral adiposity decreases in treated patients. Improvements in bone mineral density and decreases in fracture rates have also been reported, and new studies using disease-specific questionnaires provide convincing evidence that GH greatly enhances quality of life. Epidemiologic studies indicate that higher insulin-like growth factor I (IGF-I) levels may predict risk for certain cancers, but other studies suggest that lower IGF-I levels increase risk for ischemic heart disease. However, much of the community of endocrine caregivers remains skeptical of GH treatment and, therefore, a large fraction of patients with AGHD are not treated. The accumulation of long-term treatment data will be required to provide reassurance that GH treatment is a safe and necessary form of hormone replacement therapy for patients with AGHD.