Description

• Inadequate production of growth hormone (GH, also called somatotropin) in either adults or children.
• GH is a polypeptide hormone that stimulates growth and cell reproduction.
• Hypopituitarism is often used to describe GH deficiency (GHD). However, hypopituitarism is actually defined as GHD plus a deficiency in at least 1 other anterior pituitary hormone.
• Panhypopituitarism is defined as a deficiency in all the hormones produced in the pituitary gland.
• System(s) affected: Endocrine; Musculoskeletal
• Synonym(s): Hypopituitarism

Epidemiology

• Most common cause of GHD in children is idiopathic
• Most common cause of GHD in adults is a pituitary adenoma or treatment of the adenoma with surgery or radiotherapy:
  • 76% of patients with GHD had a pituitary tumor.
  • 13% had an extrapituitary tumor
  • 8% idiopathic cause
  • 1% had sarcoidosis
  • 0.5% had Sheehan syndrome

• In children, isolated GHD has been reported to affect 1 in 5,000.
• Adult-onset idiopathic GHD is extremely rare.

Risk Factors

• Transcription factor defects (POU1F1/PIT-1, PROP-1, LHX3/4, HESX-1, and PITX-2)
• GHRH receptor gene defects
• GH secretagogue receptor gene defects
• GH gene defects
• GH receptor/postreceptor defects
• Prader-Willi syndrome
• Deletion and mutation of GH-1

Pathophysiology

• GHD is caused by a complete lack of GH production or a decline in GH production. Causes can be genetic or acquired.
• Hypothalamus secretes GH-releasing hormone (GHRH), which stimulates the pituitary to secrete GH. Somatostatin is secreted by the hypothalamus to inhibit GH secretion. When GH pulses are secreted into the blood, then insulinlike growth factor (IGF)-1 is released. GHD may result from disruption of the GH axis at numerous places—in the higher brain, the hypothalamus, or the pituitary gland.

Etiology

• Congenital:
  • Genetic (see “Genetics”)
  • Structural brain defects:
    • Agenesis of corpus callosum
    • Septo-optic dysplasia
    • Empty-sella syndrome
    • Encephalocele
    • Hydrocephalus
    • Arachnoid cyst
  • Associated midline facial defects:
    • Single central incisor
    • Cleft lip/palate
• Acquired:
  • Trauma
  • CNS infection
  • Tumors of hypothalamus or pituitary:
    • Pituitary adenoma
    • Craniopharyngioma
    • Rathke cleft cyst
    • Glioma/Astrocytoma
    • Germinoma
    • Metastatic
  • Cranial irradiation
  • Pituitary infarction
  • Surgery
  • Hemochromatosis (rare)

Commonly Associated Conditions

• Macroadenoma
• Sarcoidosis
• Sheehan syndrome