poliomyelitis

introduction

·      acute viral infection

·      special localisation in

·      anterior horn cells of the spinal cord

·      certain brainstem motor nuclei

·      hallmark is muscle weakness with normal sensation

epidemiology

·      disease known for centuries

·      epidemics only recorded in past century

·      occurred in temperate countries in warmer months where there had been recent improvements in sanitation

·      rise in health standards led to decrease in the "pool of immune resistance"

·      usually in higher socio-economic groups

·      peak incidence in 5-14 age group

·      since the use of vaccines, only sporadic cases in developed countries

·      in USA, 8 cases in 1976 cf 18 000 cases in 1954

·      still a problem in third-world countries (usually in children < age 5)

·      infection is common but only a few develop paralysis (1-2%)

Immunization

·      protection against infection involves

·      direct protection of individuals

·      herd immunity

·      oral attenuated trivalent vaccine (Sabin) used

·      at 2, 4, 6 and 18 months, and at school entry

·      infection and thus immunisation occurs

·      unvaccinated children may be infected and thus become immune

·      mutation may occur and very rarely, clinical poliomyelitis develops

·      killed vaccine also exists (Salk)

·      regular boosters required

pathology

·      usually caused by one of three types of poliomyelitis virus

·      are RNA enteroviruses (Brunhilde, Lansing and Leon)

·      other enteroviruses can cause indistinguishable disease (rare)

·      humans are sole natural reservoir

·      transmitted by oropharyngeal route

·      spread by infected food or faecal matter

·      initial invasion through gastro-intestinal and respiratory tracts

·      multiplies in alimentary tract lymph nodes and spleen

·      spreads through blood

·      reaches CNS

·      involves

·      anterior horn cells of spinal cord, esp. cervical and lumbar enlargements

·      medulla, cerebellum and midbrain

·      spares

·      remainder of spinal cord

·      sacral roots

·      entire cerebral cortex

·      damage to anterior horn cells occurs due to

·      direct viral multiplication

·      toxic by-products of virus

·      results of inflammation in the surrounding glial cells

·      inflammation settles and ganglion cells dissolved by neutrophils and macrophages

·      changes largely complete at 4 months

·      involved motor unit skeletal muscle grossly atrophies

·      flaccid paralysis results

·      precentage of muscle units destroyed varies markedly

·      clinical weakness proportional to number of lost motor units

·      clinically detectable weakness present when 60% or more muscle units destroyed

·      paralysis twice as common in lower extremities than upper extremities

·      most commonly affected muscles in lower extremity are

·      quadriceps

·      glutei

·      tibialis anterior

·      medial hamstrings

·      hip flexors

·      most commonly affected muscles in upper extremity are

·      deltoid

·      triceps

·      pectoralis major

·      sacral roots spared

·      characteristic sparing of intrinsic muscles of foot

Acute stage

clinical features

·      variable incubation period (6-20 days)

·      reflects virus ingestion and multiplication

·      increased physical activity late in the incubation period leads to poorer prognosis

·      acute disease reflects viraemia

·      symptoms vary from mild malaise to generalised encephalomyelitis and widespread paralysis

·      is a clinical diagnosis (no laboratory tests)

·      in young children, there is initial malaise and fever

·      then several days of well-being

·      prodrome usually not present in older children and adults

·      then after 3-4 days, fevers recur

·      associated headache, sore throat and features of meningism

·      acute phase lasts 7-10 days

Spinal

·      onset of patchy asymmetric paralysis

·      there is spasm of opposing muscles causing pain

·      tendon reflexes disappear

·      characteristic flexor posturing

·      muscles tender to palpation

·      attempts at stretching increase reflex muscle spasm

·      no sensory changes

Bulbar

·      fullminant encephalitis with bulbar involvment may occur

·      leads to speech and swallowing problems

·      may be sudden respiratory failure from involvement of respiratory centre

Treatment

·      bed rest

·      analgaesia

·      correct anatomical positioning of limbs

·      hip 25o flexion

·      knee 20o flexion

·      ankle plantigrade

·      gentle passive range of movement

·      regular muscle charting

·      may require respiratory support

Differential diagnosis

·      Guillain-Barre syndrome

·      other forms of encephalomyelitis

Convalescent stage

clinical features

·      starts 2 days after normal temperature and cessation of paralytic disease

·      continues for 2 years

·      spontaneous improvement in muscle power occurs

·      occurs rapidly through 1st 4 months

·      more gradually after that

·      almost complete after 6th month

·      average improvement is

·      2 grades above assessment at 1 month

·      1 grade above assessment at 6 months

treatment

·      gradual increase in physical therapy programme when muscles lose sensitivity

·      physiotherapy very important

·      train co-ordination of recovering muscles

·      maintain joint mobility

·      hydrotherapy very useful

·      orthoses used sparingly to prevent deformity

·      no place for surgery

Chronic stage

clinical features

·      after 2 years

·      no further recovery

·      characteristic features

·      limb bluish, wasted and deformed

·      if disease occurred in childhood, limb may be shortened

·      limb has floppy feel

·      normal sensation

·      if trunk affected, may be scoliosis and/or respiratory insufficiency

·      problems are

·      deformity due to unbalanced paralysis

·      instability from balanced paralysis

·      deformity contributed to by growth

·      worse if disease occurs early

·      treatment aimed at managing consequences

treatment
Principles

·      prevent deformity

·      physiotherapy

·      splintage

·      stabilise flail joints

·      tenodesis

·      arthrodesis

·      splintage

·      balance imbalance

·      tendon division

·      tendon lengthening

·      tendon transfer

·      correct deformity

·      osteotomy

·      arthrodesis

Orthoses

·      orthoses used to

·      improve functional ability (eg. walking)

·      prevent paretic muscles from overstretching

·      augment action of weak muscles

Physiotherapy

·      of less use in chronic phase

·      aims to achieve maximal functional capacity through various techniques

·      active exercises

·      muscle substitution

·      passive stretching

Surgery

Aims

·      prevent deformity

·      improve function

·      eliminate or reduce orthosis requirement

Truisms

·      tendon transfer cannot overcome deformity

·      deforming forces can overcome arthrodesis

Principles

·      balanced forces and no deformity (mobile joint)

·      normal

·      imbalanced forces and no deformity (mobile joint)

·      dynamic (muscle) or static (flail and gravity)

·      soft tissue

·      tendon transfer, tenotomy or tenodesis

·      balanced forces and deformity

·      bony

·      arthrodesis (stiff joint) or osteotomy (mobile joint)

·      imbalanced forces and deformity

·      soft tissue and bony

Guidelines

·      soft tissue procedures (esp. tendon transfers) indicated in young child

·      bony procedures postponed until skeletal growth adequate

Tendon transfers

·      performed when

·      dynamic muscle imbalance sufficient to produce deformity

·      orthotic managemment required

·      performed to

·      provide active motor power to replace function of paralysed muscle

·      eliminate deforming effect of muscle when its antagonists are paralysed

·      produce stability through better muscle balance

·      principles must be followed

Adequate strength

·      to perform desired function

·      muscles of subnormal strength may be transferred if

·      they are factors in dynamic instability

·      they are combined with other muscles of subnormal strength

·      one grade of power lost

Similar strength and range of motion

·      to muscle being replaced

·      phasic (cf. antagonistic) transfers preferable

Expendable

·      loss of original function must balanced against potential gain

·      must remember strength of antagonist of removed muscle

Free passive ROM

·      at joint to be moved by transferred tendon

Absence of fixed bony deformity

·      transfer will not overcome fixed deformity

·      needs to be addressed first

Smooth-gliding channel

·      subcutaneous tunnel preferable

Intact neurovascular supply

·      by atraumatic tissue handling

Straight-line direction

·      between origin and new insertion

Sufficient tension

·      of attachment

·      allows optimal power of contraction

Factors

Donor

·      sacrificable

·      strong

·      suitable excursion

·      synergistic

Path

·      straight

·      subcutaneous

Part

·      sensate

·      stable

·      supple

Patient

·      sensible

Post-polio syndrome

·      return of

·      pain

·      fatigue

·      muscle weakness

·      functional impairment

·      30-35 yrs after original polio

·      predictive factors of recurrence

·      late onset (age >10 yrs)

·      four-extremity involvement

·      ventilator dependence

·      hospitalisation during preceding acute illness

·      may affect 20-80% of surviving patients

·      diagnostic criteria

1.   confirmed history of polio

2.   partial to complete recovery

3.   period of neurological stability for at least 15 yrs

4.   onset of 2 or more of

·      fatigue

·      muscle pain

·      new weakness

·      functional loss

·      cold intolerance

·      new atrophy

5.   no other cause

·      no specific treatment