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, arrythmias 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/