What is the difference between acromegaly and gigantism?

Difference Between Acromegaly and Gigantism

The fundamental difference between acromegaly and gigantism is the timing of growth hormone (GH) excess relative to epiphyseal closure: gigantism occurs when GH excess develops before the growth plates close (during childhood/adolescence), resulting in excessive linear growth and tall stature, while acromegaly occurs after epiphyseal fusion (in adulthood), causing enlargement of acral parts and soft tissues without increased height. 1

Key Distinguishing Features

Timing and Growth Plate Status

• Gigantism develops when GH hypersecretion occurs before epiphyseal fusion, allowing continued longitudinal bone growth and resulting in abnormally tall stature (typically >2-3 standard deviations above age/sex-matched norms) 1
• Acromegaly manifests when GH excess begins after epiphyseal closure in adulthood, when linear growth is no longer possible 1, 2, 3
• Both conditions share the same underlying etiology—most commonly a GH-secreting pituitary adenoma (somatotrophinoma)—but express differently based on skeletal maturity 1, 2

Clinical Presentation Differences

In Gigantism (Pediatric GH Excess):

• Accelerated growth velocity (>2 SDS) is the most prominent feature 1
• Abnormally tall stature defined as height >2-3 SDS above country-specific, age-appropriate, and sex-appropriate norms or >2 SDS above mid-parental height 1
• May develop acromegalic features concurrently (acral enlargement, coarsened facial features, prognathism) 1
• Pubertal delay is common due to gonadotropin inhibition from prolactin co-secretion or mass effects 1
• Delayed bone age despite tall stature 1

In Acromegaly (Adult GH Excess):

• No increase in height since growth plates are closed 3, 4
• Prominent acral enlargement (hands, feet, jaw) 1
• Coarsened facial features, frontal bossing, teeth separation, prognathism 1
• Cardiac manifestations including biventricular hypertrophy, progressing through hyperkinetic stage to eventual dilated cardiomyopathy if untreated 1

Shared Features

Both conditions can present with:

• Headache and visual field defects from mass effect 1
• Metabolic complications: insulin resistance, diabetes mellitus, hypertension 1
• Sleep apnea, carpal tunnel syndrome, joint pain 1
• Left ventricular hypertrophy and diastolic dysfunction 1
• Increased risk of colorectal neoplasia requiring colonoscopic screening starting at age 40 5

Important Clinical Pitfalls

Diagnostic Considerations

• Children with gigantism can simultaneously develop acromegalic features, creating an "acromegaly-gigantism syndrome" when GH excess persists through puberty 6
• Gigantism may be exacerbated by delayed puberty, which prolongs the period of open growth plates 1
• Nearly 50% of gigantism cases have an identifiable genetic basis (X-linked acrogigantism, McCune-Albright syndrome, Carney complex, MEN1/4, familial isolated pituitary adenoma), making genetic testing essential in children and young people 1, 2, 7

Age-Related Nuances

• The distinction is not absolute—if GH excess begins in late adolescence near the time of epiphyseal closure, patients may exhibit features of both conditions 6, 4
• X-linked acrogigantism characteristically presents with tall stature onset before age 5 (usually before age 2) with disproportionately enlarged hands and feet 1

Treatment Implications

• Both conditions require the same therapeutic approach: transsphenoidal surgery as first-line treatment, followed by medical therapy (somatostatin analogues, dopamine agonists, pegvisomant) and/or radiotherapy if needed 1
• In gigantism, suppressing growth velocity is a clinical priority, making early introduction of pegvisomant particularly beneficial 1
• Surgical success rates in experienced centers are approximately 50% for pediatric GH excess 1