The investigators will conduct a cross-sectional study of bone density, bone microarchitecture, vertebral fractures and trabecular bone score in 25 patients with acromegaly treated with Pegvisomant, the growth hormone (GH) receptor antagonist for at least 1 year and with normal insulin-like growth factor-1 (IGF-1) levels. This study aims to describe the bone architecture and associated biochemical indices of bone turnover and metabolism in patients with active acromegaly and how these are altered with treatment of the disease.

Growth hormone (GH) and Insulin-Like Growth Factor-1 (IGF-1) are important regulators of bone modeling and remodeling, fundamental to maintenance of normal skeletal integrity. In acromegaly, a disease characterized by longstanding exposure to excess GH and IGF-1, these hormones induce marked skeletal changes. Most dual energy X-ray absorptiometry (DXA) studies report that bone mineral density (BMD) is normal in acromegaly. Despite this, however, there is mounting evidence that bone health is adversely affected in patients with both active and successfully treated acromegaly.

Inclusion Criteria:

• Individuals with acromegaly
• On pegvisomant therapy with a normal IGF-1 level for at least 1 year

Exclusion Criteria:

• Malignancy (except cured basal, squamous cell skin carcinoma or other cured cancers free from recurrence > 3 years)
• Pregnancy or lactation within last 12 months
• Untreated primary hyperparathyroidism, hyper- or hypothyroidism
• Cushing's syndrome
• Prolactin-secreting pituitary adenoma
• GH deficiency
• On current drug therapy for osteoporosis
• Diabetes mellitus
• Renal insufficiency
• Liver disease
• Current or past use of glucocorticoids (more than physiologic dose), anticonvulsants, anticoagulants, methotrexate, aromatase inhibitors

25 subjects with acromegaly on pegvisomant therapy with a normal IGF-1 level for at least 1 year will be studied.

Patients will be on stable doses of any pituitary hormone supplements for 3 months prior to study entry including gonadal steroid replacement for men or premenopausal women. Hypogonadal men and premenopausal women will be replaced with clinically appropriate sex steroid replacement. Subjects will be 50% females.