acromegaly
ACROMEGALY
Acromegaly is a chronic, slowly developing disease with progressive disfigurement and disability. An early diagnosis is difficult as most signs and symptoms are due to long-standing overproduction of growth hormone &/or insulin-like growth factor (IGF-I) causing metabolic, endocrine and morphological changes.
Surgical intervention is the first-line of treatment for almost all patients with acromegaly unless there are contraindications or the patient refuses to undergo the procedure.

Evaluation

  • Visual field assessment by perimetry is suggested to be done when tumor is abut the optic chiasm on an imaging study
  • Standard biochemistry (eg glucose, calcium, phosphorus, lipid profile)
  • Sleep studies for the evaluation of sleep apnea syndrome which is frequently associated with acromegaly
  • Periodic colonoscopy surveillance
    • Recommended to be done at diagnosis since incidence of pre-malignant colonic lesions may be higher in acromegaly

Laboratory Tests

  • Random growth hormone measurement is not diagnostic due to its episodic secretion with short half-life (T½)
  • As growth hormone secretion is suppressed by glucose, measurement of growth hormone suppressibility with glucose is useful in the diagnosis of acromegaly
    • Growth hormone measurements after 75-g oral glucose load
      • Nadir growth hormone suppression after administration of glucose is considered gold standard test for acromegaly
      • Inability to suppress growth hormone to <1.0 ng/mL is considered diagnostic for acromegaly; 0.4 ng/mL for growth hormone assays with increased sensitivity
        • Clinicians should investigate the assay being used to know the sensitivity
      • Recommended to be performed at baseline, then every 30 minutes for a total of 120 minutes after administration of glucose
      • Acromegaly is suggested if growth hormone level is not suppressed to:
        • <0.3 ng/mL with immunoradiometric (IRMA) or immunochemiluminescence assay
        • <0.1 ng/mL with conventional radioimmunoassay (RIA)
    • Insulin-like growth factor-I measurements (adjusted for age and sex)
      • Good tools to assess integrated growth hormone secretion and are excellent for screening, diagnosis, and monitoring
      • Long T1/2, integrated measure of growth hormone secretion over time because levels are growth hormone dependent
      • Diagnostic if >36.4 nmol/L (280 ng/mL) for age and gender
      • Random insulin-like growth factor-I should be measured for diagnosis and for monitoring after a therapeutic intervention

Imaging

  • Performed after the above biochemical criteria for diagnosis are met
  • Magnetic resonance imaging (MRI) with gadolinium can be used for further assessment
    • Detection of tumor mass (eg pituitary adenoma)
    • Assess type, nature, size of tumor mass (eg macroadenoma or microadenoma)

Pituitary Adenoma

  • Majority of patients with acromegaly have pituitary adenoma many of which are macroadenomas
    • Growth hormone-secreting macroadenoma: >10 mm in diameter
    • Growth hormone-secreting microadenoma: <10 mm in diameter
  • Surgical cure rates are dependent on anatomy, extent and invasion of tumor and neurosurgeon expertise
  • Surgery is the treatment of choice for microadenomas and for macroadenomas that are still resectable or if they are causing visual impairment
  • Cure rates for intrasellar microadenomas can reach 75-95% and 40-68% for macroadenomas with an experienced neurosurgeon and facility
  • Control suggests growth hormone levels <1 ng/mL (with IRMA or chemiluminescence assay after an oral glucose load of 75 g of glucose orally followed by growth hormone measurements every 30 minutes for 120 minutes) and normalized age and gender matched insulin-like growth factor (IGF-I) levels and alleviation of tumor mass effects
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