Acromegaly

Acromegaly is a rare chronic endocrine disorder resulting from hypersecretion of growth hormone (GH), typically by a pituitary adenoma, which results in abnormal musculoskeletal growth that is most often noted in the face and distal extremities. Diagnosis is made on the basis of GH and insulin-like growth factor testing.

Quick Answers for Clinicians

Which testing algorithms are related to this topic?

Diagnosis

Indications for Testing

  • Adults
    • Enlarged facial or acral features, abnormal musculoskeletal growth
    • Combination of several of the following – chronic headaches, sleep apnea, bony arthritis, carpal tunnel syndrome, diabetes mellitus type 2, and hyperhidrosis (Katznelson, Endocrine Society, 2014)
  • Children
    • Accelerated linear growth (gigantism)

Laboratory Testing

  • Screening
    • Insulin-like growth factor 1 (IGF-1)
      • Most relevant test due to steady secretion
      • Highly specific if elevated
    • Growth hormone (GH)
      • Secretion is pulsatile; even morning levels may not be elevated
      • Should not be used alone to diagnose acromegaly (Katznelson, Endocrine Society, 2014)
  • Confirmation
    • Perform glucose tolerance test (GTT) and measure GH
      • Administer 75 g glucose and perform GH measurements over 120 minutes
        • Failure to suppress GH during hyperglycemia is diagnostic
        • GH <1 ng/mL excludes acromegaly
      • Clinical scenarios resulting in high GH levels and nonsuppression of GH with GTT
        High GH + Low IGF-1 High GH + Normal/High IGF-1
        Anorexia/fasting Pregnancy
        Exogenous estrogen Puberty
        Liver disease Uncontrolled hyperthyroidism
        Renal insufficiency  
        Uncontrolled diabetes mellitus  
        GH, growth hormone; GTT, glucose tolerance test; IGF-1, insulin-like growth factor 1

Histology

Imaging Studies and Procedures

  • Magnetic resonance imaging (MRI) – preferred modality to evaluate tumor presence and size
  • Computed tomography (CT) – if MRI unavailable
  • Visual field testing
    • Recommended in pregnant patients with macroadenomas (Katznelson, Endocrine Society, 2014)
    • Use if optic chiasm compression is suspected

Differential Diagnosis

Monitoring

  • Monitor growth hormone (GH) and/or insulin-like growth factor 1 (IGF-1) levels for effectiveness of therapy
    • Use the same test type for consistency, if possible
    • Target concentrations
      • GH <1 ng/mL or
      • Normal IGF-1 levels
  • GH and/or IGF-1 monitoring not recommended during pregnancy (Katznelson, Endocrine Society, 2014)

Background

Epidemiology

  • Incidence – 3-4/million (Kannan, 2013)
  • Age – mean onset 40 years
  • Sex – M:F, equal

Etiology

  • Pituitary adenomas – most common cause
  • Tumors
  • Familial disorders
  • Extrapituitary causes
    • Growth hormone-releasing hormone (GHRH)-secreting hypothalamic tumor
    • Ectopic secretion of GHRH

Pathophysiology

  • Most acromegaly is caused by sporadic GH-secreting pituitary adenomas
  • GH is synthesized in somatotroph cells of the anterior lobe of pituitary gland
    • Pulsatile secretion
  • GH secretion is regulated by the hypothalamus
    • Stimulated by GHRH
    • Inhibited by somatostatin
  • Circulating GH stimulates synthesis and secretion of insulin-like growth factor 1 (IGF-1) from the liver
  • IGF-1 inhibits GH secretion at the pituitary and hypothalamus level, creating a negative feedback loop
  • Pituitary tumors mimic stimulation of adenylyl cyclase by GHRH receptor activation
    • Causes autonomous GH secretion
    • Symptoms are related to excess GH and IGF-1 secretion and to expansion of the pituitary mass

Clinical Presentation

  • Indolent course – delay in diagnosis of 4-10 years
  • Symptoms of pituitary mass expansion
    • Headaches
    • Visual field defects
    • Cranial nerve palsies
    • Symptoms consistent with hypopituitarism due to compression of remaining pituitary gland by expanding mass
  • Symptoms of GH excess
    • Musculoskeletal
      • Hypertrophic arthropathy – both axial and peripheral skeleton
      • Carpal tunnel syndrome
      • Bony overgrowth
        • Coarse facial features, macrognathia, frontal bossing
        • Spade-shaped hands
        • Enlarged feet
        • Mandibular overgrowth – prognathia
        • Open epiphyses in children – linear bone growth causes gigantism
      • Obstructive sleep apnea – due to soft tissue overgrowth (eg, macroglossia)
    • Cardiovascular
      • Hypertension
      • Cardiomyopathy – biventricular hypertrophy
      • Arrhythmias
    • Dermatologic
      • Acanthosis nigricans
      • Hyperhydrosis
    • Metabolic
    • Neoplastic
  • Familial acromegaly
    • MEN1
      • Autosomal dominant inheritance
      • ~10% incidence of GH-producing tumors
    • McCune-Albright syndrome
      • Rare
      • Triad of peripheral precocious puberty, café-au-lait spots, fibrous dysplasia of the bone
      • Thyrotoxicosis
    • Carney complex
      • Rare
      • Pigmented skin, myxoma, cardiac myxoma, thyroid nodules or carcinoma, primary pigmented nodular adrenocortical disease
      • ~10% incidence of GH-producing tumors
    • Familial isolated pituitary adenoma
      • More common for childhood onset – frequent presentation is gigantism
      • Higher growth rate than with sporadic tumors

ARUP Lab Tests

Primary Tests

Aid in diagnosis of growth hormone excess or deficiency disorders

Use to diagnose gestational diabetes mellitus, diabetes mellitus, or impaired glucose tolerance

Aid in diagnosis of growth hormone excess or deficiency disorders

Aid in histologic diagnosis of acromegaly

Stained and returned to client pathologist; consultation available if needed

Related Tests

Not a first-line test in the evaluation of growth disorders

Aid in workup of suspected anterior hypopituitarism

Medical Experts

Contributor

References

Additional Resources