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 Testing 

  • Visual field assessment by perimetry is suggested to be done when tumor is abut the optic chiasm on an imaging study
  • It is also performed if the patient complains of reduced peripheral vision

Other Studies

  • Standard biochemistry (eg glucose, calcium, phosphorus, lipid profile, serum prolactin level)
  • 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

Biochemical Tests

  • Insulin-like growth factor-I (IGF-1)
    • IGF-1 mesurements (adjusted for sex and age) are recommended initial screening as they are good tools to assess integrated growth hormone secretion and are excellent for screening, diagnosis, and monitoring
      • Recommended initial screening in patients with clinical manifestations of acromegaly especially those with facial and acral features
      • Also recommended in patients with associated conditions such as sleep apnea syndrome, type 2 diabetes mellitus, debilitating arthritis, carpal tunnel syndrome, hyperhidrosis and hypertension
    • May be used to rule out acromegaly in patients with pituitary mass
    • Long T1/2, integrated measure of growth hormone secretion over time because levels are growth hormone dependent
    • Diagnostic if >280 ng/mL with adjustments for age and gender
    • Normal IGF-1 effectively rules out the diagnosis of acromegaly
      • In pregnancy and late-stage adolescence, false positives may occur
    • Random insulin-like growth factor-I should be measured for diagnosis and for monitoring after a therapeutic intervention
  •  Growth Hormone
    • Random growth hormone measurement is not diagnostic due to its episodic secretion and 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; <0.3 ng/mL for nadir 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)
Pathological Findings

Growth Hormone-Staining Pituitary Adenoma

  • Majority of patients with acromegaly have pituitary adenoma many of which are macroadenomas
    • GH-secreting macroadenoma: >10 mm in diameter
    • GH-secreting microadenoma: <10 mm in diameter
  • Surgery is the treatment of choice for microadenomas and macroadenomas that are still resectable or if they are causing visual impairment

Imaging

  • Performed after the above biochemical criteria for diagnosis are met
  • Magnetic resonance imaging (MRI) with gadolinium of the pituitary gland is the initial choice of imaging modality
    • Detection of tumor mass (eg pituitary adenoma)
    • Assess type, nature, size of tumor mass (eg macroadenoma or microadenoma)
  • CT scan is the next choice of imaging modality if MRI is contraindicated
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