Acromegaly Diagnosis

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

Biochemical Tests

• Insulin-like growth factor-1 (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 T_1/2, 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-1 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 (T_½)
  • 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
    • 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)
        
    • Recommended to be performed at baseline, then every 30 minutes for a total of 120 minutes after administration of glucose

• Response to medical treatment may be the same as their biologically active counterparts
• May help predict response to dopamine agonist therapy in tumors that stain for prolactin

• 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
  
  • Detect tumor mass (eg pituitary adenoma)
  • Assess type, nature, size of tumor mass (eg macroadenoma or microadenoma)
    • GH-secreting macroadenoma: >10 mm in diameter
    • GH-secreting microadenoma: <10 mm in diameter
• CT scan is the next choice of imaging modality if MRI is contraindicated