Growth Hormone Deficiency & Excess for USMLE 1
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Growth Hormone Deficiency & Excess for the USMLE Step 1 Exam
Growth Hormone Deficiency (GHD)
- Etiology
- Congenital: GH deficiency can result from genetic mutations (e.g., GH1 gene) or developmental issues affecting the hypothalamus or pituitary gland.
- Acquired:
- Pituitary Tumors: Compression or destruction of somatotroph cells by pituitary adenomas.
- Trauma, Surgery, or Radiation: Injury or radiation to the hypothalamic-pituitary axis can lead to reduced GH production.
- Infiltrative Diseases: Conditions like sarcoidosis or Langerhans cell histiocytosis can impair GH secretion.
- Clinical Features
- Children:
- Growth Failure: Short stature due to decreased linear growth velocity.
- Delayed Puberty: Sexual development may be delayed.
- Adults:
- Decreased Muscle Mass: Loss of lean body mass and increased fat mass.
- Osteoporosis: Reduced bone density due to the lack of anabolic effects of GH on bone.
- Impaired Cardiovascular Health: Increased cardiovascular risk from dyslipidemia and decreased cardiac output.
- Diagnosis
- Stimulation Tests:
- Insulin Tolerance Test (ITT): GH response to insulin-induced hypoglycemia.
- Arginine Stimulation Test: Arginine infusion should stimulate GH release.
- Low IGF-1 Levels: Indicates insufficient GH activity.
- MRI: To assess pituitary structure for tumors or other abnormalities.
- Treatment
- Recombinant GH Therapy: Used for both children and adults to improve growth (in children) and body composition and quality of life (in adults).
- Monitoring: Regular assessment of IGF-1 levels and side effects such as insulin resistance or joint pain.
Growth Hormone Excess (Acromegaly and Gigantism)
- Etiology
- Pituitary Adenoma: The most common cause, typically a somatotroph adenoma that leads to autonomous GH secretion.
- Ectopic GHRH Production: Rarely, tumors outside the pituitary (e.g., bronchial carcinoid) secrete growth hormone-releasing hormone (GHRH), stimulating GH production.
- Clinical Features
- Acromegaly (Adults):
- Skeletal Changes: Enlargement of hands, feet, jaw, and facial bones.
- Soft Tissue Growth: Thickened skin, macroglossia, and organomegaly (e.g., hepatomegaly).
- Cardiovascular Disease: Hypertension, left ventricular hypertrophy, and increased cardiovascular mortality.
- Metabolic Effects: Insulin resistance and increased risk of diabetes mellitus.
- Gigantism (Children):
- Excessive Linear Growth: Rapid increase in height due to prolonged growth of long bones before epiphyseal closure.
- Diagnosis
- Elevated IGF-1: Persistently elevated IGF-1 reflects chronic GH excess.
- Oral Glucose Tolerance Test (OGTT): GH fails to suppress after oral glucose in cases of GH excess.
- MRI: Used to identify pituitary adenomas or other masses.
- Treatment
- Transsphenoidal Surgery: Primary treatment for pituitary adenomas, aiming to remove the tumor and normalize GH levels.
- Medications:
- Somatostatin Analogs: Octreotide or lanreotide inhibit GH secretion.
- GH Receptor Antagonists: Pegvisomant blocks GH receptors, reducing IGF-1 levels.
- Radiation Therapy: Considered if surgery and medications are not sufficient to control the disease.
Key Points
- Growth Hormone Deficiency (GHD):
- Common causes include pituitary tumors, trauma, and congenital defects.
- In children, it presents with growth failure; in adults, with reduced muscle mass, bone density, and cardiovascular health.
- Diagnosis includes low IGF-1 and GH stimulation tests (ITT, arginine).
- Treatment involves recombinant GH therapy.
- Growth Hormone Excess:
- Most often caused by pituitary adenomas, resulting in acromegaly in adults or gigantism in children.
- Key symptoms include skeletal overgrowth, cardiovascular complications, and insulin resistance.
- Diagnosis is based on elevated IGF-1 and failed suppression of GH in an OGTT.
- Treatment includes surgery, somatostatin analogs, and GH receptor antagonists.