Poliomyelitis

Overview – Poliomyelitis

Poliomyelitis is a highly infectious viral disease caused by the poliovirus, historically responsible for widespread paralytic illness in children. Although largely eradicated in developed countries through vaccination programs, poliomyelitis remains a critical differential diagnosis for acute flaccid paralysis. This page outlines the transmission, pathogenesis, clinical features, and prevention of poliomyelitis for final-year medical students.

Definition

Poliomyelitis is an infectious neurotropic disease caused by the poliovirus, which targets motor neurons in the spinal cord and brainstem, resulting in asymmetrical flaccid paralysis in a small percentage of cases.

Aetiology

• Poliovirus (an enterovirus, RNA virus)
• Spread via:
  • Faecal-oral route
  • Respiratory droplets

Epidemiology

• Virtually eradicated in most developed countries
• A single confirmed case is considered a public health emergency
• Endemic in a few regions globally (e.g. parts of Afghanistan and Pakistan)

Prevention

Vaccines

• Oral Polio Vaccine (OPV) – Live attenuated
  • Advantages: Easy oral administration
  • Disadvantages: Rare risk of vaccine-associated paralytic polio (VAPP) (~1 in 2.5 million)
• Inactivated Polio Vaccine (IPV) – Killed virus
  • Advantages: No risk of VAPP
  • Disadvantages: Requires injection

Pathophysiology

1. Poliovirus enters via ingestion or inhalation
2. Replicates in the gastrointestinal tract
3. Spreads to bloodstream
4. Invades the anterior horn cells of the spinal cord
5. Causes neuronal destruction → flaccid paralysis

Clinical Features

• 90% asymptomatic
• <10% develop minor viral illness:
  • Fever, headache
  • Neck/back pain
  • Vomiting, lethargy
  • Abdominal discomfort
• ~1% develop CNS involvement:
  • Asymmetrical flaccid paralysis with areflexia
  • Spinal polio → limb paralysis (commonly legs, often unilateral)
  • Bulbar polio → cranial nerve involvement (e.g. dysphagia, dysphonia, dyspnoea)
  • Mixed forms also possible

Investigations

• Throat/stool viral cultures or PCR for poliovirus
• CSF analysis: elevated WBC, mildly raised protein
• MRI spine: may show anterior horn inflammation
• Clinical diagnosis often based on characteristic presentation + travel history

Management

• Supportive care only (no antiviral treatment)
  • Pain management
  • Physiotherapy and orthotic support
  • Mechanical ventilation (if respiratory failure)
• Long-term rehab may be needed for residual deficits
• Prevention via vaccination is the mainstay of control

Complications

• Permanent paralysis
• Respiratory failure
• Post-polio syndrome (years later)
• Contractures and limb deformities
• Psychosocial disability

Differential Diagnosis

• Guillain-Barré syndrome
• Transverse myelitis
• Acute flaccid myelitis
• Botulism
• Spinal cord injury

Summary – Poliomyelitis

Poliomyelitis is a vaccine-preventable viral disease that can cause asymmetrical flaccid paralysis through destruction of spinal motor neurons. Most cases are asymptomatic, but severe forms can lead to lasting disability or death. Though eradicated in most developed regions, polio remains a notifiable disease of international concern. For a broader context, see our Nervous System Overview page.