Other Neuromuscular Conditions

Arthrogryposis Multiplex Congenita

Aetiology

  • Non-progressive disorder
  • Lack of anterior horn cells
  • Myopathic, neuropathic, or mixed

Diagnosis

  • Confirmed by:
    • Enzyme tests
    • Nerve conduction studies (NCS)
    • Muscle biopsy at 3 months

Features

  • Multiple joint contractures – joints lack skin creases
  • Normal facies
  • Normal intelligence
  • No visceral involvement

Affected Body Areas

  • Upper Limbs:
    • Shoulder internal rotation and adduction
    • Elbow extension contractures
    • Management:
      • Leave one arm extended
      • Manipulation under anesthesia (MUA) & serial casting
      • Release and supracondylar osteotomy
      • One arm for feeding, other for self-care
  • Hips:
    • Teratologic dislocations
    • Open reduction +/- femoral shortening or VDRO
  • Knees:
    • Early release of hamstrings
  • Feet:
    • Congenital vertical talus and rigid club foot
    • Will not respond to casting
    • Open release; if unsuccessful – talectomy
    • Aim for a plantigrade, shoeable foot
  • Spine:
    • C-shaped large curve scoliosis
    • May need fusion to pelvis if progressing

Distal Arthrogryposis Syndrome

  • Autosomal dominant
  • Similar features to Arthrogryposis Multiplex Congenita
  • Hands and feet more affected than proximal joints

Larsen’s Syndrome

  • Similar to Arthrogryposis Multiplex Congenita but contractures are milder
  • Features:
    • Multiple dislocated joints
    • Cervical spine kyphosis:
      • May progress and cause myelopathy

Multiple Pterygium Syndrome

  • Joint contractures with webbing on the flexor aspect
  • Surgical caution:
    • Neurovascular bundle close during release of webs

Friedrich’s Ataxia

Characteristics

  • Most common spinocerebellar disorder
  • Autosomal recessive
  • Lack of Frataxin protein
  • Affects mitochondria
  • Onset: 10–15 years
  • Death: By 50 years (cardiomyopathy)

Clinical Features & Management

  • Staggering, wide-based ataxic gait
  • Increased polyphasic waveforms on NCS
  • Cardiomyopathy
  • Cavovarus/Equinovarus – stiff:
    • Require fusions
  • Scoliosis:
    • Needs fusion due to aggressive progression (not always down to pelvis)

Spinal Muscular Atrophy (SMA)

Characteristics

  • Most common genetic disease causing pediatric death
  • 1 in 10,000 live births
  • Loss of anterior horn cells in the spinal cord
  • Autosomal recessive

Classification

  • SMA1:
    • Onset <6 months
    • Death by 2 years (respiratory failure)
  • SMA2:
    • Onset <24 months
    • Life expectancy: 15–20 years
  • SMA3:
    • Onset >24 months
    • Normal life expectancy
    • Independently stands

Clinical Features & Management

  • Weakness develops from proximal to distal
  • Hip Dislocations:
    • Usually asymptomatic; non-operative treatment
  • Scoliosis:
    • Severe, progressive
    • Large curves causing respiratory compromise
    • Aggressive treatment with long fusions
    • May reduce walking capability
  • Feet:
    • Equinovarus common
    • Aim for pain-free, plantigrade, shoeable foot
    • Use tenotomy & osteotomy rather than transfer

Polio

  • Viral infection causing loss of anterior horn cells in spine and brainstem
  • Features:
    • Often unilateral
    • No sensory deficit
    • Weakness and smaller limb typical
  • No new cases since vaccination, but sequelae still treated

Hereditary Motor Sensory Neuropathies

Charcot-Marie-Tooth Disease (CMT)

Aetiology

  • Autosomal dominant disorder causing predominantly distal motor and sensory deficits
  • Family history often positive

Types

  1. HSMN 1 (CMT – Myelopathic/Hypertrophic):
    • More common
    • Onset: 10–20 years
    • Demyelination of nerves
    • Nerve conduction studies: Prolonged latencies, reduced velocities
    • Absent reflexes
  2. HSMN 2 (CMT – Neuropathic):
    • Less common
    • Onset: 20–30 years
    • Wallerian degeneration without demyelination
    • EMGs: Near normal
    • Present reflexes
  3. HSMN 3 (Dejerine-Sottas Disease):
    • Autosomal recessive
    • Onset: Infancy
    • More severe manifestations:
      • Foot drop
      • Scoliosis
      • Difficulty ambulating

Clinical Features of All Types

  • Motor > sensory affliction
  • Most affected muscles: Peronei and Tibialis Anterior
  • Predominantly foot symptoms:
    • Cavus, Cavovarus, hammer toes
  • Management:
    • Surgery aims to maintain flexibility with transfers/osteotomy
    • Avoid fusion where possible – young patients
  • Rare Features:
    • Hip dislocation
    • Scoliosis
    • Intrinsic wasting of hands

Guillain-Barre Syndrome

  • Idiopathic post-viral polyneuropathy
  • Features:
    • Symmetric ascending motor neuropathy
    • Self-limiting
    • Death by respiratory failure

Hemihypertrophy

  • Unilateral limb hypertrophy
  • Idiopathic cause
  • Associated with:
    • Neurofibromatosis Type 1 (NF1)
    • Renal abnormalities (e.g., Wilm’s tumor)

Klippel-Trenaunay Syndrome

  • Hemihypertrophy with associated hemangiomas and AV malformations
  • Management:
    • Amputation or embolization often necessary

Proteus Syndrome

  • Overgrowth of hands and feet with spinal deformity
  • Bizarre facial features
  • Must differentiate from NF1 and McCune-Albright Syndrome
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