Endocrinology · Pituitary Disorders
The facts most likely to be tested
Acromegaly is most commonly caused by a pituitary somatotroph adenoma resulting in chronic excess growth hormone (GH) secretion.
The initial screening test of choice is an elevated serum insulin-like growth factor-1 (IGF-1) level.
The confirmatory diagnostic test is the oral glucose tolerance test (OGTT), where failure to suppress GH levels below 1 ng/mL is diagnostic.
Clinical presentation classically includes acral overgrowth (enlarged hands/feet), macroglossia, prognathism, and increased hat or shoe size.
Patients are at significantly increased risk for colonic polyps and colon cancer, necessitating early and frequent colonoscopy screening.
The first-line treatment for symptomatic patients is transsphenoidal surgical resection of the pituitary tumor.
Medical management for patients who are not surgical candidates or have persistent disease includes somatostatin analogs (e.g., octreotide) or GH receptor antagonists (e.g., pegvisomant).
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A 48-year-old male presents to the clinic complaining that his wedding ring no longer fits and he has had to purchase larger shoes over the past two years. He also reports increased sweating and persistent headaches. Physical examination reveals coarse facial features, macroglossia, and prognathism. His blood pressure is 155/95 mmHg. Laboratory studies show an elevated IGF-1 level.
What is the most appropriate next step to confirm the diagnosis?
Oral glucose tolerance test (OGTT)
The patient's clinical presentation is classic for acromegaly; while IGF-1 is the best screening test, the OGTT is the gold standard for confirming the diagnosis by demonstrating a failure of GH suppression.
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High yield triage
Etiology / Epidemiology
Caused by pituitary adenoma hypersecreting GH. Occurs in adults after epiphyseal closure.
Clinical Manifestations
Features acral overgrowth, macroglossia, and prognathism. Look for increased shoe/glove size.
Diagnosis
IGF-1 is the best screening test. Oral glucose tolerance test (OGTT) is the gold standard.
Treatment
Transsphenoidal surgery is first-line. Octreotide is the primary medical therapy.
Prognosis
Increased cardiovascular mortality. Monitor IGF-1 levels post-operatively.
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Epidemiology & Etiology
Acromegaly is a rare, chronic condition typically caused by a benign pituitary somatotroph adenoma. It occurs in adults after the fusion of the epiphyseal plates, distinguishing it from gigantism. Incidence is roughly 3-4 cases per million per year, often diagnosed in the 4th or 5th decade of life.
Pertinent Anatomy
The tumor originates in the anterior pituitary gland within the sella turcica. Mass effect can compress the optic chiasm, leading to bitemporal hemianopsia. Local expansion may also cause hypopituitarism by compressing adjacent hormone-secreting cells.
Pathophysiology
Excessive Growth Hormone (GH) secretion stimulates the liver to produce Insulin-like Growth Factor-1 (IGF-1). Chronic elevation of IGF-1 drives systemic tissue proliferation and metabolic changes. This leads to insulin resistance, often resulting in secondary diabetes mellitus.
Clinical Manifestations
Patients present with coarsening of facial features, macroglossia, and prognathism. Classic signs include increased shoe, ring, or glove size and carpal tunnel syndrome. Red flags include obstructive sleep apnea, hypertension, and colon polyps requiring screening colonoscopy.
Diagnosis
Screening begins with an elevated serum IGF-1 level. The Oral Glucose Tolerance Test (OGTT) is the gold standard; failure to suppress GH to <1 ng/mL confirms the diagnosis. MRI of the brain with gadolinium is the imaging modality of choice to localize the adenoma.
Treatment
Transsphenoidal surgery is the first-line treatment for most patients. If surgery is unsuccessful or contraindicated, Octreotide (a somatostatin analog) is the preferred medical therapy. Pegvisomant is a GH-receptor antagonist used for refractory cases, but requires monitoring for elevated liver enzymes.
Prognosis
Untreated acromegaly leads to increased cardiovascular mortality due to cardiomyopathy and arrhythmias. Patients require lifelong monitoring of IGF-1 levels and periodic echocardiograms. Successful treatment should normalize IGF-1 levels to age-adjusted ranges.
Differential Diagnosis
Gigantism: occurs before epiphyseal closure
Hypothyroidism: presents with myxedema and fatigue
Pachydermoperiostosis: rare genetic disorder with skin thickening
Drug-induced: high-dose estrogen or glucocorticoid use
Ectopic GHRH secretion: rare neuroendocrine tumors