Poliomyelitis is an acute infectious disease caused by the Poliovirus belonging to entero virus family and produces a wide variety of symptoms ranging from muscular paralysis, non-paralytic illness to meningeal involvement.
Poliomyelitis occurs in both sporadic and epidemic manner. Its maximum incidence is in temperate countries. The seasonal incidence is in the hottest months of the year (Late summer and early autumn). It mainly involves young children and most of those affected are below 5 years of age. Infants below one year of age appear to be immune from the disease. Children of both sexes are affected though male children are involved more frequently as compared to females.
There are three sero types of virus. Type 1 (brunhilda) Type II (lansing) and Type III (Leon). All three are responsible for paralytic form of polio though affection with typ I is more common. There is no cross immunity between the three sero types.
The virus has specific predilection for anterior born cells of the grey matter of the spinal cord and the motor nuclei of the brain stem. Man is the only reservoir of the virus and it is mainly spread by faeco oral route and droplet infection.
After entering the body, Poliomyelitis virus proliferates in the lympathic tissue in the nasopharynx and gut resulting in the production and secretion of IgA antibodies which provide local immunity. Virus reaches the central nervous system by blood – CNS barrier, giving rise to symptoms of meningeal involvement. Other route of entry is via motor neurones at peripheral neuromuscular junctions.
Changes in nervous system are mainly in the anterior horn cells of the spinal cord and the motor nuclei of the brain stem which are swollen, congested and show degenerative changes (necrosis of neuronal cells, perivascular cuffing) and infiltration with cells mainly lymphocytes. The basal ganglia and cerebral cortex are little affected.
Clinical features of Poliomyelitis
The incubation period varies from 7 to 14 days and may be longer. Human contact is important cause of spread of infection either by droplet infection or faeco oral route. Clinically three forms of polio are recognized.
1. Minor illness or abortive cases
2. Preparalytic stage/non-paralytic
3. The paralytic stage
(a) Spinal form
(b) Bulbar form
(c) Polio encephalitis
Minor illness or Abortive case
Poliomyelitis occurs sporadically especially at times of epidemics. Symptoms are non specific such as mild fever, headache, malaise, aching in the limbs, sore throat and mild gastro intestinal symptoins. These symptoms subside within 2 to 3 days and more than 90% of patients do not proceed beyond this minor form of ifiness (Forme’s Frustes).
Non-paralytic preparalytic stage of Poliomyelitis
Here symptoms of minor form of the disease are more intense and prolonged. These include pains in the back and limbs, fever, vomiting, diarrhoea etc. After a day or so features of meningeal irritation in the form of neck rigidity and photo phobia appear. Delirium may develop and child may show involuntary muscular jerks and ataxic tremors.
CSF shows increased pressure with a moderate increase in proteins and increase in cell count. Non- paralytic form of polio generally subsides and recovery takes place within a week.
It consists of spinal, bulbar forms or a combination of both.
This follows rapidly pre-paralytic stage and is characterized by paralysis of muscles preceded by muscular cramps and twitchings. Fasciculations may be observed. Muscles of the neck, trunk and all four limbs may be involved.
Weakness is asymmetrical and some muscles of the body may be affected more than others. Paralysis of muscles is flaccid, lower motor neuron type with loss of motor power. Reflexes are either diminished or absent. Muscles are tender and show spasm leading to development of contractures.
Usually maximum damage is done within the first twenty four hours and the muscles first affected show maximum degree of permanent damage. It is in ascending form of the Poliomyelitis disease there is upward involvement from legs, lower trunk to upper limbs and respiratory muscles leading to respiratory paralysis.
Cases who survive, the final picture is that of paralysis of different group of muscles. Paralyzed muscles undergo atrophy and are flaccid. These muscles which are rapidly paralyzed their chances of recovery are little. Faradic stimulation of muscles shows reaction of degeneration and any muscle which shows a response to Faradic current after 3 weeks of onset of illness, will usually recover completely.
Rarely in spinal form, the disease may involve white matter of lateral columns giving rise to involvement of pyramidal tracts as well spino thalamic tracts producing a picture of BrownSequard’s syndrome. This leads to spastic paralysis of limbs as well as loss of pain, heat and cold sensations.
Tenderness in muscles and pain in moving the joints may persist for several weeks.
In a small percentage of cases of Poliomyelitis involvement of lower cranial nerves in the brain stem may occur. There is dysphagia, dysarthria, regurgitation of fluids down the nose. Laryngeal paralysis may be partial or complete. Facial paralysis may develop. Ocular palsies are not common. Nystagmus occurs in short bursts and at rapid rhythm.
Involvement of nuclei in medullary reticular formation is of grave importance since it may lead to dysfunction of cardiac and respiratory centers which results in grave complications threatening life. If the patient survives from this form of illness, cranial nerves recover completely.
This is a combination of spinal and bulbar form of polio with picture resembling encephalitis (alterations in consciousness, convulsions). The disease carries grave prognosis.
Diagnosis of Poliomyelitis
In early stage of polio where symptoms are of minor nature in the form of fever, malaise, headache etc diagnosis of Polio is difficult since the whole picture may simulate a case of FLU. The non-paralytic form of polio has to be differentiated from conditions producing aseptic meningitis.
Cases of paralytic form have to be differentiated from Guillain-Barre syndrome. Acute transverse myelitis and acute intermittent porphyria. In the presence of muscular atrophy and wasting, differentiation shall be form myopathy, progressive muscular atrophy or syringomyelia.
But clinical features and CSF changes in polio shall make the diagnosis easier. The virus can be isolated from the CSF in few cases. Serological diagnosis is made by demonstration of rising titre of viral antibodies and complement fixing antibodies in the serum and CSF.
Treatment of Poliomyelitis shall fall under three phases:
1. Acute illness lasting from onset to 2-3 weeks.
2. Stage of neuronic recovery lasting from 6 months from the onset.
3. Stage of adaptation and rehabilitation.
Patient should be nursed in a manner that rest is provided to sore muscles. Analgesics and local heat shall give symptomatic relief. All muscles showing weakness or paralysis should be put in a position of physiological rest. Gentle passive movements are the only form of physical treatment.
Since there is no specific treatment of Poliomyelitis only supportive measures are adopted. Patient’s pulse, blood pressure, respiration should be monitored to detect any problem of respiratory functions. Intramuscular injections should be avoided since combined with undue exertion, these may provoke paralysis.
When managing paralyzed muscles, aim should be to prevent their stretching and contracture of their antagonists. Patient be nursed on a firm bed and the paralyzed muscles kept in a position of relaxation. As the patient improves and passes into a stage of convalescence active exercises of muscles be advised.
Respiratory failure is the dreaded complication which develops suddenly within 2 to 3 days of paralysis. Such cases should be managed in an intensive care unit where patient may have to be put on ventilator depending on vital capacity.
In determining the first onset of respiratory weakness is by finding as to how many times the patient can count in one expiration. But oximeter is the correct way to decide about ventilation. Cases of Bulbar Polio in the absence of respiratory paralysis have collection of secretions in the pharynx and there is danger of their being aspirated into the lungs.
Patient suffering from Poliomyelitis should be nursed in semi prone position and turned from side to side at frequent intervals. Secretions should be sucked mechanically and patient fed through naso gastric tube. Parenteral administration of fluids and nutrients should be under taken.
After the acute phase is over, recovery starts taking place. This period may last from 3 to 6 months. Main aim at this stage is to promote maximal recovery of nerve cells. Massage and passive movements of limbs combined with active physiotherapy is employed to prevent wasting and contractures of muscles. Care must be taken to prevent the development of deformities. After 6 months the chances of recovery are little and improvement becomes slow.
Deformities of limbs may develop in severely paralysed cases. The affected limb may fail to grow and even becomes shorter as compared to normal side. Instrumental devices may be used to improve functions of the limbs. After 2 years, orthopaedic surgery help is required to improve functions of the paralyzed limbs.
Prevention of Poliomyelitis
Poliomyelitis is a preventable disease. Two types of vaccines are available – inactivated killed vaccine (Salk) which is given parenterally and live oral attenuated virus vaccine (Sabin). Each of these vaccines contains the three serotypes of polio virus.
Of the two, live oral vaccine is the most commonly used. It is given in four doses at birth, 6 weeks, 10 weeks and 14 weeks of age. It produces antibodies to all three sero types in more than 90% of cases. Booster doses are recommended at the age of one and half and 5 years to maintain adequate antibody levels.
Inactivated polio vaccine (IPV) also has excellent efficiency. Three doses of the vaccine are given subcutaneously at 1, 2 and sixth month. A booster dose at the time of entry to school is also recommended. This vaccine gives protection for at least 5 years.
Out of these two vaccines, oral polio vaccine (OPV) is the preferred one and is especially useful for mass immunization. Only disadvantage of the vaccine is the production of vaccine associated paralytic disease.
It is due to emergence of circulating vaccine derived polio virus strains (CVDPV). These strains are able to transmit the disease from person to person and cause a disease indistingushable from wild type polio virus. The incidence of this complication is miniscule (1 in 2.6 million). It mainly occurs in immuno compromised persons.
Mass immunization of children below the age of 5 years and provision of clean water supply, eradication of flies and adopting good hygienic measures are other methods, of preventing Poliomyelitis.
Post polio syndrome
It is a form of progressive muscle weakness which usually develops after many years after an acute attack of polio. Symptoms are variable ranging from mild to moderate and consist of fatigue, joint, pains and weakness. It may stabilize or progress to atrophy of muscles. Probably it is due to dysfunction of surviving motor neurons.