Diagnosis of Acromegaly. How is Acromegaly diagnosed?
Acromegaly Diagnosis is done with the following lab investigations.
A. Growth Hormone Assay for Acromegaly Diagnosis:
Radioimmunoassay shows increased basal growth hormone levels (Normal up to 10 ng/ml) Basal levels are not sufficient to diagnose acromegaly.
Dynamic testing is often required. Here 100 gm glucose load is given and blood for growth hormone is collected after 60 minutes.
Post glucose growth hormone is the most definitive test to establish the diagnosis of acromegaly. Glucose suppresses growth hormone and is therefore used for dynamic testing.
Post glucose growth hormone value above 2 raises a strong possibility of a growth hormone producing tumor. Often blood glucose is collected basal, 1 hour and 2 hours during the same test to rule out associated diabetes.
Females on oral contraceptives may show false positive results. Similarly elevated GH levels occur in renal failure, cirrhosis of liver, protein caloric malnutrition and anorexia nervosa. But here the clinical features of acromegaly are absent.
2. Plasma somatomedin C (Insulin like Growth Factor – IGFi) levels
Plasma somatomedin C (Insulin like Growth Factor – IGFi) levelsare also increased in acromegaly and provide good correlation with the clinical manifestation of GH hyper secretion.
IGF-1 (Insulin like growth factor-1) and IGF-BP3 (insulin like growth factor binding proteins) are now available and used to screen, diagnose and monitor post-operative case of acromegaly. These values are elevated.
B. Radiological Changes for Acromegaly Diagnosis:
1. Skull (Lateral view):
(a) Enlargement of the pituitary fossa with double floor.
(b) Erosion of the clinoid processes.
(c) Prominence of jaw and supra-orbital ridges.
(a) Tufting arrow-head appearances of the terminal phalanges.
(b) Heel-pad thickness is increased (more than 17 mm) .
3. Spine: Kyphoscoliosis and osteoporosis.
C. Biochemical for Acromegaly Diagnosis:
1. Elevation of serum phosphorus and alkaline phosphatase
2. Increased urinary calcium and hydroxyproline.
D. To Detect Parasellar Involvement
1. Fundus Examination: Optic atrophy and papilledema.
2. Perimetry: Bitemporal hemianopia and enlargement of the blind spot.
3. CT Scan brain with 2 mm pituitary cuts may suffice especially in cases of macroadenomas. However MRI scan especially with gacloleneum contrast is the most sensitive available test.
ASSESSMENT OF THE ACTIVITY OF ACROMEGALY
A. Elevated Post Glucose Growth Hormone Levels: This is the most definite index of activity.
B. Clinical Features: Increasing size of gloves, rings, shoes and hat; poor fit of the dentures and excessive seborrhoea and sweating are evidences of secretary activity of the adenoma.
C. Biochemical: Elevated serum phosphorus and alkaline phosphatase and elevated urinary hydroxyproline.
D. Biopsy of Costal Cartilage may show active endochondral bone formation.