July 13, 2010

MRCP 1 Question 20

A 40 year old female presents to her physician with a goitre.

On examination, the physician finds signs suggestive of acromegaly including coarse oily skin, a large tongue, prognathism and a prominent supra-orbital ridge of the face.

Examination of the hands revealed thick, spade fingers.

Which of the following should be the initial hormonal diagnostic investigation:

a) insulin levels
b) growth hormone
c) arginine levels
d) growth hormone releasing hormone
e) insulin-like growth factor 1 (IGF-1)

The correct answer is E


Since Serum GH levels vary considerably in different individuals, and in the same person at different times, measurement of random or basal GH levels are not of value in making the diagnosis of acromegaly.

IGF-1 is a growth factor produced by the action of growth hormone on the liver, kidney, muscle, pituitary and GI tract.

GH exerts its effects indirectly through IGF-1 (formerly called somatomedin-C).

Serum levels of IGF-1 may be considered a mean of the 24 hour levels of growth hormone, and is not affected by the pulsatile release of GH.

It is thus a useful screening test for acromegaly.

Suppression of GH levels by glucose is the confirmatory test for acromegaly (Suppression of GH levels to < 2 mcg/L by RIA or < 1 mcg/L by IRMA 60 - 120 minutes after a 100 gram glucose load is diagnostic).

Rare cases of acromegaly may be caused by ectopic production of GHRH, but it's measurement is not needed routinely.

As always, radiological investigation should follow biochemical diagnosis (partly because of the high prevalence of pituitary incidentalomas).

MRI is the method of choice for imaging the pituitary because of it’s excellent resolution

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