Review Question - QID 221303

This patient who presents with arthralgias, enlargement of the hands, progressive dyspnea, poorly controlled hypertension, multiple skin tags, and coarse facial features most likely has acromegaly. The most appropriate next step in the diagnosis of acromegaly is the measurement of insulin-like growth factor-1 (IGF-1) levels.

Acromegaly is a condition caused by the excessive secretion of growth hormone (GH), usually due to a pituitary somatotroph adenoma. It can also present with signs of heart failure, hyperhidrosis, enlarged organs, carpal tunnel syndrome, visual field defects, and diverticulosis. Most of the clinical manifestations of acromegaly are caused by IGF-1 levels, which are secreted due to GH stimulation of the liver. Unlike GH levels, which fluctuate throughout the day, IGF-1 levels remain elevated throughout the day and are thus the preferred initial test for acromegaly following clinical suspicion. If IGF-1 levels are elevated, an oral glucose suppression test is conducted as a confirmatory test. If there is inadequate GH suppression after a glucose load, a brain MRI is obtained to evaluate for pituitary lesions. Treatment for acromegaly includes pituitary surgery, radiotherapy, and medications to reduce growth-hormone hypersecretion, such as dopamine agonists and somatostatin analogs.

Trainer et al. studied the use of the growth-hormone receptor antagonist pegvisomant in the treatment of acromegaly. They found that pegvisomant therapy leads to the normalization of IGF-1 levels in 89% of patients. They recommend the use of pegvisomant in patients with acromegaly who are unable to undergo surgery or have progression of disease after transsphenoidal surgery.

Figure/Illustration A is a clinical photograph that shows frontal bossing and coarse facial features (red circle). This finding is consistent with a diagnosis of acromegaly.

Incorrect Answers:
Answer 1: Growth hormone (GH) level is an inappropriate initial test for acromegaly because GH levels fluctuate throughout the day. Thus, it cannot be used alone in the diagnosis of acromegaly.

Answer 3: MRI of the pituitary gland should be conducted only after the diagnosis of acromegaly has been made using IGF-1 levels and confirmed with an oral glucose suppression test. Since incidental pituitary lesions can be found in asymptomatic patients, an MRI may yield a false positive as an initial diagnostic tool.

Answer 4: Oral glucose suppression growth hormone test is the next step in confirmatory diagnosis for patients found to have elevated IGF-1 levels. In normal conditions, the administration of an oral glucose load suppresses GH secretion and thus reduces IGF-1 levels. In acromegaly, GH will not be suppressed.

Answer 5: Thyrotropin-releasing hormone administration suppresses GH levels in normal patients but can increase GH secretion in patients with acromegaly. This test is not routinely performed due to poor sensitivity.

Bullet Summary:
Insulin-like growth factor-1 level is the most appropriate initial test in the diagnosis of acromegaly.