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Poliomyelitis

  • A disease caused by viral destruction of the  anterior horn cells in the spinal cord and brain stem motor nuclei
  • The hallmark is motor weakness with normal sensation

Epidemiology

  • Eliminated from the western hemisphere
  • Vaccine-related poliomyelitis is responsible for most modern day cases
  • More common in tropical countries – in late summer months

Etiology

  • Caused by the poliovirus
    • RNA virus from the picornaviridae family
    • Serotype 1, 2 and 3 are disease causing
  • Faecal-oral transmission – by ingestion of contaminated food/water
  • Incubation period is 6-20 days
  • Risk factors – immune deficiency, malnutrition, pregnancy

Pathophysiology

  • Poliovirus enters the body through oral ingestion
  • Then enters and replicates in the gastrointestinal tract – gains entry by binding to CD155 (the poliovirus receptor)
  • Continues to replicate in enterocytes for about a week
  • From there it spreads to the tonsils, Peyer’s patches and the deep cervical and mesenteric lymph nodes
    • Subsequently absorbed into the bloodstream (viremia) – leads to widespread dissemination in the body

Spinal polio

  • Due to viral invasion of the motor neurons of the anterior horn cells (grey matter)
  • Invasion leads to inflammation of the nerve cells, causing damage and destruction of motor neuron ganglia
    • Leads to muscle atrophy, and eventually paralysis
    • Sensation in the paralysed limbs is preserved

Bulbar polio

  • Due to viral invasion and destruction of the nerves within the bulbar region of the brainstem
    • Most commonly infected cranial nerves – glossopharyngeal n. (CN IX), vagus n. (CN X) and accessory n. (CN XI)
    • Causes paralysis of the muscle groups innervated by these nerves, especially those of the soft palate and pharynx

Bulbospinal polio

  • Both bulbar and spinal symptoms
  • Virus affects C3-C5 and the phrenic nerve
  • Leads to paralysis of the diaphragm – patient is unable to breathe without a ventilator

Clinical features – 3 presentations

Asymptomatic/mild illness – 95% of cases

  • Sore throat, fever, nausea, vomiting, abdominal pain, flu-like symptoms

Non-paralytic aseptic meningitis

  • Headache, nuchal rigidity, abdominal pain
  • Fever, vomiting, lethargy

Paralytic polio

  • Spinal – affects muscles of the trunk, limbs and the intercostals muscles
    • Asymmetric flaccid paralysis – worsens over hours to days
    • Paralysis is usually more severe in proximal muscles than in distal
  • Bulbar
    • Symptoms of encephalitis, dysphagia, dyspnoea
    • Pooling of secretions in the airways – can cause suffocation
    • Facial weakness, double vision
  • Bulbospinal
    • Respiratory failure

Diagnosis

  • Virus culture from stool, CSF or nasopharynx
  • CSF analysis (lumbar puncture) – shows lymphocytosis and elevated protein level
  • Serology
  • MRI of spinal cord
  • EMG of affected limb

Complications

  •  Equinus foot – similar to club foot
    • When the muscles that pull the foot down (plantar flexors) are intact – gastrocnemius, soleus, plantaris, FHL, FDL, tibialis posterior
    • But the muscles that pull the foot up (dorsi flexors) don’t function – tibialis anterior, EHL, EDL
    • Eventually there is tightening of the Achilles tendon
  • Osteoporosis
  • Increased risk of bone fractures

Treatment

  • Antibiotics – to prevent infections in weakened muscles
  • Analgesia
  • Physiotherapy
  • Ventilators

Foot deformities

  • Orthoses
  • Operative – contracture release, tendon transfer, arthrodesis

Post-polio syndrome

  • Occurs in 25-50% of people who have previously recovered from paralytic polio in childhood
  • Occurs from 10-40 years after initial polio infection

Pathogenesis

    • During recovery from polio, neurons in affected muscles re-grow smaller branches (dendrites)
    • These dendrites take over the function of neurons destroyed by the virus
    • After years of functioning beyond capacity, these neurones weaken and lose ability to maintain the dendrites
    • Leads to muscle weakness

Clinical features

  • Gradual deterioration of muscle function
  • Muscle weakness
  • Fatigue, muscle pain, twitching
  • Cold intolerance

Treatment

  • Walking aides – canes, walkers
  • Physiotherapy and gentle exercise (swimming)
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