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Condition/Disorder Synonyms

  • Bulbospinal muscular atrophy

  • Hereditary neuronopathy

  • Progressive muscular atrophy1

  • Werdnig-Hoffman disease

ICD-9-CM Codes

  • 335.0 Werdnig-Hoffman disease

  • 335.1 Spinal muscular atrophy

  • 335.10 Spinal muscular atrophy, unspecified

  • 335.19 Other spinal muscular atrophy

ICD-10-CM Codes

  • G12.0 Infantile spinal muscular atrophy, type I [Werdnig-Hoffman]

  • G12.8 Other spinal muscular atrophies and related syndromes

  • G12.9 Spinal muscular atrophy, unspecified

Preferred Practice Pattern

Key Features


  • Group of four subtypes of degeneration of anterior horn cells that results in progressive muscle atrophy

    • Spinal muscular atrophy (SMA I), Werdnig-Hoffman (acute)

    • Spinal muscular atrophy (SMA II), Werdnig-Hoffman (chronic)

    • Spinal muscular atrophy (SMA III), Kugelberg-Welander

    • Spinal muscular atrophy (SMA IV)

Essentials of Diagnosis

  • Autosomal recessive genetic disorder that results in a lack of survival motor neuron gene1 on chromosome 5q11.2-132

General Considerations

  • SMA type I: weakness between birth and 3 months of age

  • SMA type II: signs and symptoms by 3 years of age

  • SMA type III: signs and symptoms between 2 to 9 years of age

  • SMA type IV: adult onset


  • Type I: 27% of all SMA cases

  • Types II and III: 46% of all SMA cases

  • Type IV: 8% of all SMA cases

  • Werdnig-Hoffman 1:10,000 births

  • Kugelberg-Welander 6:100,000 births

Clinical Findings

Signs and Symptoms

  • Fasciculations (especially of tongue)

  • Muscle weakness

  • Hypotonia

  • Muscle atrophy

  • Decreased or absent deep tendon reflexes

  • Difficulty feeding (infant)

  • Lack of extension during Landau reflex

  • Contractures (type 1)

  • Scoliosis

  • Trendelenburg sign during gait

Functional Implications

  • Inability to sit independently

  • Inability to ambulate

  • Require assistance with ADLs

Possible Contributing Causes

  • Autosomal recessive genetic disorder on chromosome 5q11.2-132

Differential Diagnosis

  • Muscular dystrophy

  • Guillain-Barré

  • Brachial plexus birth injury

  • Other genetic syndromes

Means of Confirmation or Diagnosis

Laboratory Tests

  • Genetic testing


  • Plain radiograph for scoliosis

Diagnostic Procedures

  • Electromyography (EMG)

  • Muscle biopsy




  • Geneticist

  • Occupational therapist


  • Head lag when infant pulled into a sitting position from supine

  • Poor head control

  • Inability to sit

  • Inability to pull to stand

  • Inability to walk

  • Contractures of biceps and wrist flexors

Tests and Measures


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