Acromegaly Diagnosis
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-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 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-1 should be measured for diagnosis and for monitoring after a therapeutic intervention
- 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
- 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
- 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
Growth Hormone-Staining Pituitary Adenoma
- 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
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
- 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