Poliomyelitis

Question 1

Examination findings of poliomyelitis

Answer 1

LMN pattern unilateral/bilateral flaccid paraparesis with hypoplastic, hypotonia and hyporeflexia
Muscular weakness with **normal** sensation
Foot drop

A. Inspection - functional deficit and modified ADLs
1. Walking aids, splints, ankle support and orthoses
2. Scuffing at front of shoes (foot drop)

B. Unilateral (rarely bilateral) lower limb more common than upper limb
1. Hypoplastic limb(s) with proximal and distal wasting
2. Hypotonia
3. Hyporeflexia/areflexia, absent plantar response
4. Muscle weakness - proximal and distal
5. Normal sensation
6. Pes cavus on affected lower limb
7. Previous surgical scars over ankle and foot
- Tendon transportation for foot drop
- Joint fixation - arthrodesis -> fixed joint
- Joint replacement surgery of hip and knee

C. Chronicity
1. Hypoplastic, atrophied muscles
2. Shortening of limbs
- Childhood - limb shorter (growth impairment)
- Adulthood - no shortening
3. Fasciculations
- Acute: fasciculations (will not occur in PACES)
- Post-polio syndrome: fasciculations after late progressive wasting disease
- Chronic polio: NO fasciculations

D. Complications
- Arthritis and spinal degenerative disorders (tenderness)
- Scoliosis

Question 2

What are the differentials if there is chronic bilateral limb weakness?

Answer 2

1. Bilateral poliomyelitis is rare but plausible
2. Motor neuropathy - MMN
3. Motor neuron disease - PMA
4. HSMN - if there is SENSORY deficit

Question 3

What are the differentials if there is acute flaccid limb weakness/paralysis?

Answer 3

A. Infection
1. Poliomyelitis, enterovirus 71, Coxsackie A7
2. Japanese encephalitis
3. West Nile virus
4. Tick paralysis
5. Rabies
6. Botulism
7. Diphtheria
8. Lyme disease

B. Neuropathy
1. GBS (AIDP)
2. Acute intermittent porphyria
3. Lead poisoning
4. Buckthorn poisoning

C. Spinal disease
1. Acute transverse myelitis
2. Spinal cord compression
3. Spinal cord infarction

Question 4

Poliovirus is an __ from __ family.
Description: (strand)(acid) with __ protein, WITHOUT lipid envelope
-> Resistant to lipid solvent, stable at low pH

Strains: __ (commonest __)

Answer 4

Enterovirus, Picornaviridae
Single stranded RNA, caspid protein

3 strains (type 1-3)
Type 1 commonest (80%)

Question 5

Pathophysiology of poliomyelitis
- Transmission
- Replication
- Dissemination

Answer 5

Transmission: faeco-oral route - ingestion of contaminated water

Replication: in oropharyngeal and gastrointestinal mucosa during incubation period (1-3 weeks)

Dissemination: drains into cervical and mesenteric LN and enters bloodstream, then crosses BBB into nervous system, axonal transportation from peripheral nerve

Only 5% develops poliomyelitis

Question 6

Clinical syndromes of polio infection (5)

Answer 6

1. Abortive poliomyelitis (95%)
   - Asymptomatic or mild symptoms of pharyngitis or gastroenteritis
2. Non-paralytic (pre-paralytic) poliomyelitis
   - Headache, fever, sore throat, GI symptoms
   - Meningism (irritability, neck and back stiffness)
   - Lasts for 1-2 weeks
   - May progress to paralytic polio
3. Paralytic poliomyelitis
   - Flaccid limb paresis and atrophy
   - Subjective paresthesia (objective sensation intact)
   - Recovery may be complete / partial / absent
4. Paralysis with bulbar involvement
   - Children with tonsils and adenoids removed may experience pure bulbar involvement without limb involvement
   - Bulbar with spinal involvement in adults
   - Dysphagia, dysphonia, facial weakness
   - Respiratory failure and vasomotor disturbance (cardiovascular instability) if brainstem reticular formation affected
5. Encephalitis
   - Rare, high mortality - agitation, confusion, stupor, coma

Question 7

Post-polio syndrome

Answer 7

Progressive wasting and weakness many years after poliomyelitis (as long as 30 years)

Postulated ongoing viral replication or reactivation

Question 8

Vaccination for prevention of poliomyelitis

Answer 8

1. Inactivated - Sabin vaccine
   - 3 strains of inactivated viruses, given by injection
   - Stimulates IgM, IgG and IgA production
   (not secretory IgA)
2. Oral live attenuated - Salk vaccine
   - 3 strains of live but attenuated viruses, given orally at 2, 4 and 6 months, booster 4-6 years old
   - Attenuated infection of oropharynx and gut, stimulates IgM, IgG and IgA production
   (includes secretory IgA)
   - Excretion of live viruses and may result in vaccine associated paralytic poliomyelitis in unimmunised immunocompromised closed contact