Acromegaly

Detailed Overview

Acromegaly develops slowly over decades. The persistent elevation of GH and IGF-1 induces somatic hypertrophy, metabolic dysfunction (insulin resistance, diabetes mellitus), and cardiovascular disease (cardiomyopathy, hypertension). Because the growth plates are closed, patients do not grow taller (unlike gigantism in children), but instead experience acral enlargement (hands, feet, jaw). Cardiovascular and respiratory complications are the leading causes of premature mortality if untreated. Early diagnosis is often missed due to the insidious phenotypic changes.

Epidemiology & Demographics

Incidence: 3-4 cases per million person-years. Prevalence: 40-70 cases per million. Average age at diagnosis is 40-50 years, with a diagnostic delay of 5-10 years. Equal prevalence in males and females.

Etiological Mechanism

>95% of cases are caused by a sporadic, benign, monoclonal GH-secreting pituitary macroadenoma (>1cm). Rare causes include ectopic GH or GHRH secretion from neuroendocrine tumors (e.g., pancreatic islet cell, bronchial carcinoid).

Primary Causes

Pituitary somatotroph adenoma

MEN-1 syndrome (Multiple Endocrine Neoplasia type 1)

McCune-Albright syndrome

Ectopic GHRH secretion (carcinoid tumor)

• Genetic syndromes: Familial isolated pituitary adenoma (FIPA) with AIP gene mutations, MEN-1, or Carney complex.

A mutation in the GNAS1 gene (in sporadic cases) causes constitutive activation of the stimulatory G-protein alpha subunit (Gs-alpha), leading to continuous cAMP generation and uninhibited somatotroph proliferation and GH secretion. Excess circulating GH binds to hepatic GH receptors, stimulating the synthesis and release of IGF-1. IGF-1 mediates most of the somatic growth-promoting effects, causing chondrocyte and osteoblast proliferation, leading to periosteal bone apposition, soft tissue swelling, and visceromegaly (enlarged heart, thyroid, liver). GH itself directly antagonizes insulin, leading to lipolysis and hyperglycemia.

Characteristic Clinical Presentation

• Acral changes: Gradual increase in ring, glove, and shoe sizes.
• Facial changes: Coarsening of facial features, prominent brow (frontal bossing), and enlarged jaw (prognathism).
• Hyperhidrosis: Excessive and malodorous sweating due to sweat gland hypertrophy.
• Headaches & Visual changes: Caused by the mass effect of the pituitary tumor compressing the optic chiasm (bitemporal hemianopsia).

Physical Examination Signs

• Macroglossia (enlarged tongue) leading to sleep apnea
• Spade-like hands with doughy consistency
• Widely spaced teeth (diastema) and jaw malocclusion
• Skin tags (acrochordons) and acanthosis nigricans
• Deep, hollow-sounding voice (vocal cord hypertrophy)

• Acromegalic cardiomyopathy: Biventricular hypertrophy and diastolic dysfunction leading to heart failure.
• Obstructive Sleep Apnea (OSA): Due to macroglossia and pharyngeal soft tissue hypertrophy.
• Colonic polyps: Increased risk of colon adenomas and colon cancer.

Diagnostic Criteria & Guidelines

1. Elevated serum IGF-1 level for age and sex (best initial test). 2. Failure of GH suppression to < 1 ng/mL following a 75g oral glucose tolerance test (OGTT) (confirmatory test).

Differential Diagnosis

• Familial prognathism
• Pachydermoperiostosis
• Severe hypothyroidism (myxedema)
• Paget disease of bone

Laboratory Tests & Biomarkers

• Serum IGF-1: Markedly elevated (e.g., > 300-500 ng/mL depending on age range)
• GH after 75g OGTT: Fails to suppress; nadir GH > 1 ng/mL
• Prolactin: Elevated in ~30% of cases due to co-secretion or stalk compression

Imaging Modalities & Findings

• MRI of Pituitary with Gadolinium: Defines the size and extent of the pituitary adenoma, often showing a macroadenoma invading the cavernous sinus.
• X-ray of hands/feet: Tufting of the terminal phalanges (arrowhead appearance), increased soft tissue thickness.

• Microadenoma
  Tumor < 10 mm. Symptoms primarily biochemical/metabolic without local mass effect.
• Macroadenoma
  Tumor > 10 mm. High likelihood of local compression (optic chiasm) and invasive growth.

Second-Line & Adjunctive Therapy

Medical therapy if surgery fails or is contraindicated: Somatostatin analogs (Octreotide LAR 20-30 mg IM every 4 weeks, or Lanreotide Autogel 120 mg deep SC every 4 weeks). GH receptor antagonists (Pegvisomant 10-30 mg SC daily).

Surgical & Procedural Management

Endoscopic transsphenoidal adenomectomy. Stereotactic radiosurgery (Gamma Knife) is reserved for persistent tumor remnant after surgery and medical therapy.

Recommended Lifestyle Changes

• Use a CPAP machine for symptomatic obstructive sleep apnea.
• Strict blood pressure and blood glucose monitoring due to high risk of secondary diabetes and hypertension.
• Routine dental care for malocclusion.

Patient Counseling & Advice

Advise that while surgery and medications can halt the progression and reverse soft-tissue swelling, the bony changes (jaw, hands) are irreversible. Emphasize the importance of lifelong monitoring for tumor recurrence and cardiovascular complications.

Follow-Up & Monitoring Schedule

Measure IGF-1 and GH levels 12 weeks post-op. Annual screening for cardiovascular disease (Echocardiogram). Colonoscopy every 3-5 years due to increased polyp risk. Regular visual field testing if tumor nears the optic chiasm.

Preventive Strategies

No primary prevention exists. Secondary prevention relies on early recognition of the physical changes to prevent irreversible cardiovascular and bony complications.

With successful treatment normalizing IGF-1 and GH, mortality rates return to that of the general population. Uncontrolled disease doubles the mortality rate, primarily from cardiovascular events.