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