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Updated: Dec 17 2020

Werdnig-Hoffman Syndrome

  • Snapshot
    • An infant is brought to the pediatrician by his mother due to muscle weakness. The mother reports that the infant’s weakness has progressively worsened. He is unable to sit unsupported, has a weak cry and suck. On exam, there is fasciculations of the tongue and fingers with absent deep tendon reflexes. Molecular genetic testing for the SMN gene is ordered.
  • Introduction
    • Also known as infantile spinal muscle atrophy (SMA)
      • most common and severe of the SMA disorders
      • degeneration of the anterior horn → muscle weakness
        • lower brain stem and spinal cord
      • autosomal recessive mutation in the SMN1 gene
      • may present in utero
        • mother may notice decreased (or absent) fetal movement late in pregnancy
  • Epidemiology
    • Commonly presents in the neonatal period
    • Median survival is 7 months
      • onset at birth
  • Presentation
    • Symptoms
      • symmetric flaccid paralysis
        • most affected infants are hypotonic at birth
        • proximal muscle involvement
          • lower extremity greater than upper extremity
      • sparing of upper cranial nerves
        • e.g., normal eye movements
    • Physical exam
      • absent or decreased deep tendon reflexes
      • tongue and finger fasciculatons
      • infants have flaccid "frog like" posture
      • restrictive respiratory insufficiency
  • Evaluation
    • Molecular genetic testing
      • confirms the diagnosis
    • Electromyography (EMG)
      • fibrillations and sharp waves
    • Muscle biopsy
  • Differential
    • Congenital myasthenia syndromes
    • Congenital myopathy
  • Treatment
    • Supportive
      • ensure nutritional support and respiratory assistance
      • manage weakness
  • Prognosis, Prevention, and Complications
    • 95% death by 18 months of age and 100% by four years of age
    • Development of kyphosis and scoliosis
    • Weakened pulmonary muscles
      • decreased respiratory support from musculature
      • can lead to hypoxia and CNS damage
    • Malnutrition
      • from difficulty in food intake
    • Immobility
      • combination of muscle weakness and degeneration along with a host of other orthopedic problems such as scoliosis
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