DWARFISM - Complete Study Guide for MUHS PG Medicine Theory Exam

QUICK DEFINITION

• Campbell's Operative Orthopaedics 15th Ed 2026
• Adams and Victor's Principles of Neurology, 12th Ed

CLASSIFICATION

A. By Body Proportions

1. Short-trunk variety - trunk shorter relative to limbs
   • Example: Kniest syndrome (spondyloepiphyseal dysplasia)
2. Short-limb variety - limbs disproportionately short; trunk relatively normal
   • Example: Achondroplasia, diastrophic dysplasia
   • Short-limb dwarfism is further subclassified by which segment is short:
     • Rhizomelic - proximal limb (humerus/femur) is short
     • Mesomelic - middle segment (radius-ulna/tibia-fibula) is short
     • Acromelic - distal segment (hands/feet) is short

• Miller's Review of Orthopaedics 9th Ed

CAUSES / ETIOLOGY

1. Endocrine Causes (Proportionate)

2. Genetic / Skeletal Dysplasias (Disproportionate)

3. Metabolic / Nutritional

• Mucopolysaccharidoses (storage disorders) - proportionate dwarfism
• Nutritional dwarfism (malnutrition, celiac disease, Crohn's disease)
• Renal osteodystrophy

4. Psychosocial Dwarfism

• Also called Kaspar-Hauser syndrome, maternal deprivation syndrome, or abuse dwarfism
• Growth retardation from emotional/psychological neglect
• Associated with retarded bone age and osteopenia
• Reversible with change in environment
• Brogdon's Forensic Radiology

5. Chromosomal / Syndromic

• Turner syndrome (45,X0) - short stature, gonadal dysgenesis
• Down syndrome (Trisomy 21)
• Russell-Silver syndrome - prenatal onset short stature, hemihypertrophy, craniofacial dysostosis
• Seckel (bird-headed) dwarfism - microcephaly, beaked nose, severe cognitive impairment (mutation in RAD3-related protein)

DETAILED PATHOPHYSIOLOGY

A. GH Deficiency Dwarfism (Pituitary Dwarfism)

Hypothalamus (GHRH)
      ↓
Anterior Pituitary (GH)
      ↓
Liver (IGF-1 / Somatomedin-C)
      ↓
Bone epiphyseal plates → Linear growth

• Decreased GHRH (hypothalamic dysfunction)
• Primary GH deficiency (pituitary)
• Failure to generate IGF-1 (liver)
• GH receptor defects or IGF-1 receptor defects

• Proportionate short stature
• Body proportions normal
• Mild obesity (lack of fat mobilization)
• Delayed puberty
• No sexual development in 2/3 of patients; 1/3 do mature sexually
• Normal intelligence
• Delayed bone age
• Guyton & Hall Textbook of Medical Physiology; Costanzo Physiology 7th Ed

B. Laron Dwarfism (GH Resistance)

• GH levels are elevated (not deficient)
• GH receptors are defective - cannot generate IGF-1
• Treatment with exogenous GH is INEFFECTIVE
• Treatment requires recombinant IGF-1
• Costanzo Physiology 7th Ed

C. Achondroplasia (Most Common Skeletal Dysplasia)

• Disproportionate short stature (limbs << trunk)
• Rhizomelic shortening (proximal limb segments most affected)
• Enlarged head with frontal bossing
• Depression at root of nose (saddle nose)
• Relatively normal trunk
• Normal intelligence
• Normal lifespan (usually)
• Foramen magnum narrowing - can cause spinal cord compression, sleep apnea
• Lumbar spinal stenosis - claudication and leg symptoms in adults
• Trident hand - fingers appear to diverge in three groups

• Short, wide long bones
• Champagne glass pelvis (narrow sacroiliac notch)
• Bullet-shaped vertebrae
• Decreasing interpedicular distance from L1 to L5 (reversed in normal)
• Robbins & Kumar Basic Pathology; Bailey and Love's Surgery 28th Ed; Adams & Victor's Neurology

D. Thanatophoric Dysplasia

• Most common lethal form of dwarfism
• Also FGFR3 gain-of-function mutation, but more severe than achondroplasia
• Incidence: 1 in 20,000 live births
• Severe limb shortening, frontal bossing, macrocephaly
• Small chest cavity → respiratory insufficiency → death at birth or soon after
• Robbins & Kumar Basic Pathology

INVESTIGATIONS

For Proportionate Short Stature (Endocrine Work-Up)

1. Bone age (X-ray wrist) - delayed in GH deficiency, hypothyroidism; advanced in precocious puberty
2. Serum IGF-1 (Somatomedin-C) - best screening test for GH deficiency (stable, not pulsatile)
3. Serum IGFBP-3 - low in GH deficiency
4. GH stimulation tests (definitive):
   • Insulin tolerance test (gold standard)
   • Arginine stimulation
   • Clonidine stimulation
   • L-DOPA stimulation
5. Thyroid function tests (TSH, free T4)
6. Karyotype - in girls to rule out Turner syndrome
7. MRI pituitary - to look for craniopharyngioma, tumors
8. Serum cortisol - to rule out Cushing's
9. IGF-1 generation test - if Laron syndrome suspected (high GH, low IGF-1, no response to exogenous GH)

For Disproportionate Short Stature (Skeletal Dysplasia Work-Up)

1. Skeletal survey X-rays (whole body)
2. Molecular genetic testing (FGFR3 for achondroplasia)
3. MRI spine/foramen magnum (in achondroplasia - assess stenosis)
4. CT pelvis/femur (if arthroplasty planned)

TREATMENT

Pituitary (GH Deficiency) Dwarfism

• Guyton & Hall; Lippincott Illustrated Reviews Pharmacology; Katzung Pharmacology 16th Ed

• GH deficiency
• Turner syndrome
• Prader-Willi syndrome
• Chronic renal insufficiency (children)
• Small for gestational age (SGA)
• Idiopathic short stature (ISS)

Achondroplasia

• No cure currently
• Vosoritide (CNP analog, C-type natriuretic peptide) - recently approved to increase height velocity in children with achondroplasia
• Limb lengthening procedures (Ilizarov technique) used in some centers
• Foramen magnum decompression if symptomatic stenosis
• Spinal stenosis management

Hypothyroid Dwarfism

• Early thyroxine replacement (irreversible cognitive damage if untreated)

IMPORTANT EPONYMS & SPECIAL TYPES

HIGH-YIELD MNEMONICS

• M - Metabolic / nutritional
• U - Unknown (constitutional)
• T - Turner syndrome / chromosomal
• C - Chronic illness (renal, GI, cardiac)
• D - Dysmorphic syndromes / Dysplasias / Deficiency of GH

• Rhizomelic = pRoximal (e.g., achondroplasia)
• Mesomelic = Middle
• Acromelic = distal (Acral)

EXAM-FORMAT WRITTEN ANSWER

• Short-trunk variety: e.g., spondyloepiphyseal dysplasia (Kniest syndrome)
• Short-limb variety: e.g., achondroplasia, diastrophic dwarfism
  • Further subclassified as rhizomelic (proximal), mesomelic (middle), or acromelic (distal)

1. Endocrine: GH deficiency (panhypopituitarism), Laron dwarfism (GH resistance), hypothyroidism, Cushing's syndrome, precocious puberty
2. Skeletal dysplasias: Achondroplasia (FGFR3 gain-of-function mutation, AD), thanatophoric dysplasia (most common lethal form), diastrophic dwarfism (AR), osteogenesis imperfecta
3. Chromosomal: Turner syndrome (45,X0), Down syndrome, Russell-Silver syndrome
4. Nutritional: Malnutrition, celiac disease, inflammatory bowel disease
5. Psychosocial: Deprivation/Kaspar-Hauser syndrome - reversible with treatment
6. Constitutional: Familial short stature, constitutional delay of growth and puberty

1. Bone age X-ray (wrist)
2. Serum IGF-1 and IGFBP-3 (screening for GH deficiency)
3. GH stimulation tests (insulin tolerance test - gold standard)
4. Thyroid function tests (TSH, free T4)
5. Karyotype (girls - to rule out Turner syndrome)
6. MRI pituitary (rule out craniopharyngioma)
7. Skeletal survey X-rays (for skeletal dysplasias)
8. Molecular genetic testing (FGFR3 in achondroplasia)

• Foramen magnum stenosis (achondroplasia) - sleep apnea, sudden death, quadriplegia
• Lumbar spinal stenosis - claudication
• Premature osteoarthritis of hip
• Scoliosis (especially in diastrophic dwarfism - 88%)
• Psychological and social morbidity

SOURCES

• Guyton & Hall Textbook of Medical Physiology, p. 924-925
• Costanzo Physiology 7th Ed, p. (GH Pathophysiology section)
• Robbins & Kumar Basic Pathology (Achondroplasia, Thanatophoric Dysplasia)
• Adams and Victor's Principles of Neurology 12th Ed, p. 1016
• Bailey and Love's Short Practice of Surgery 28th Ed
• Campbell's Operative Orthopaedics 15th Ed 2026, p. 290
• Miller's Review of Orthopaedics 9th Ed

1. Achondroplasia = most common skeletal dysplasia; FGFR3 gain-of-function; AD; 90% new mutations on paternal allele
2. Thanatophoric dysplasia = most common LETHAL dwarfism; also FGFR3 but more severe
3. Laron dwarfism = high GH + low IGF-1; GH receptor mutation; treat with IGF-1 not GH
4. Psychosocial dwarfism = reversible with change in environment
5. GH is species-specific - must use recombinant human GH
6. Diastrophic dwarfism = AR; scoliosis in 88%
7. Short-limb segments: Rhizomelic (proximal) > Mesomelic > Acromelic