Acute flaccid myelitis

Background

• Polio-like illness, subset of transverse myelitis
• More common in children
• Likely caused by:
  • Enterovirus, particularly Enterovirus D68, poliovirus
  • West nile virus
  • Adenovirus

Clinical Features

• Acute onset, focal weakness of 1 or more extremity
• Decreased muscular tone
• Absent or hypoactive reflexes
• Rarely have numbness, but may have some neuropathic pain
• Fever and other symptoms of infection by causative virus (e.g. URI symptoms, gastroenteritis)
• In severe cases:
  • Bulbar dysfunction (dysphagia, dysarthria, dysphonia, facial weakness, ptosis)
  • Respiratory muscle weakness
  • Autonomic instability, arrhythmias if cervical lesion present
• Paralysis usually maximal at 3-5 days after onset

Differential Diagnosis

Weakness

• Neuromuscular weakness
  • Upper motor neuron:
    • CVA
    • Hemorrhagic stroke
    • Multiple sclerosis
    • Amyotrophic Lateral Sclerosis (ALS) (upper and lower motor neuron)
  • Lower motor neuron:
    • Spinal and bulbar muscular atrophy (Kennedy's syndrome)
  • Spinal cord disease:
    • Infection (Epidural abscess)
    • Infarction/ischemia
    • Trauma (Spinal Cord Syndromes)
    • Inflammation (Transverse Myelitis)
      • Acute flaccid myelitis
    • Degenerative (Spinal muscular atrophy)
    • Tumor
  • Peripheral nerve disease:
    • Guillain-Barre syndrome
    • Toxins (Ciguatera)
    • Tick paralysis
    • Diabetic peripheral neuropathy
  • Neuromuscular junction disease:
    • Myasthenia gravis crisis
    • Botulism
    • Organophosphate toxicity
    • Lambert-Eaton myasthenic syndrome
  • Muscle disease:
    • Rhabdomyolysis
    • Dermatomyositis
    • Polymyositis
    • Alcoholic myopathy
• Non-neuromuscular weakness
  • Can't miss diagnoses:
    • ACS
    • Arrhythmia/Syncope
    • Severe infection/Sepsis
    • Hypoglycemia
    • Periodic paralysis (electrolyte disturbance, K, Mg, Ca)
      • Hypokalemic periodic paralysis
      • Thyrotoxic periodic paralysis
    • Respiratory failure
  • Emergent Diagnoses:
    • Symptomatic Anemia
    • Severe dehydration
    • Hypothyroidism
    • Polypharmacy
    • Malignancy
    • Aortic disease - occlusion, stenosis, dissection
  • Other causes of weakness and paralysis
    • Acute intermittent porphyria (ascending weakness)

Evaluation

• Evaluate for other causes of symptoms (e.g. HSV, bacterial meningitis, Guillain-Barre syndrome)
• CSF: Pleocytosis (WBC count >5 cells/mm³), +/- elevated protein
• MRI: spinal cord lesion, largely restricted to gray matter, spanning one or more spinal segments
  • Spinal cord lesions may not be present on initial MRI if performed within the first 72 hours of onset of acute limb weakness.

Management

• Report suspected cases to CDC/department of health
• Respiratory:
  • Consider intubation for airway protection if evidence of bulbar dysfunction
  • Consider NIPPV if evidence of respiratory muscle weakness (by clinical exam, hypoxia, hypercarbia, vital capacity <15 mL/kg, or NIF <30)
• Treat neuropathic pain
• Elevate head of bed >30 degrees
• No evidence of benefit from corticosteroids, IVIG, plasmapheresis, or antivirals as of yet

Disposition

• Admit
• Consider ICU admission for:
  • Respiratory muscle weakness
  • Bulbar weakness causing impaired airway protection
  • Altered mental status
  • Autonomic instability
  • Cervical lesion on MRI
  • Rapidly progressive course

See Also

• Weakness
• Enterovirus D68
• Transverse myelitis

External Links

• https://wwwn.cdc.gov/nndss/conditions/acute-flaccid-myelitis/case-definition/2018/