A neurological illness that comes a few days after any form of viral illness (viz. measles, chicke-npox etc.) is most likely an ADEM. The symptoms are related to the cerebrum, cerebellum or spinal cord. The incidence is 1 in 2000 patients of viral illness. Occasionally such illness may follow vaccination for rabies etc. The incidence of ADEM tends to be more in children.
In some cases memory ‘impairment or behavioural disorders persist while in some seizure disorder may be precipitated. Prognosis is good in adult patients and in those with cerebellar symptoms.
This disease is different from the viral infections directly damaging the brain. There is no direct or microscopic evidence of viral infection and the symptoms start after 2 to 20 days of virus infection. It is a post viral sequalae:
It is believed to be due to decrease in the resistance power of the body (i.e. Immune-mediated). However, newer tests available can elicit DNA links to the virus.
Restlessness, confusion, disorientation,drowsiness or seizures can occur. The patients may also have headache, fever, unsteadiness or myoclonic jerks. Some patients may have altered sensorium loss of consciousness or respiratory problems.
In this type of illness, symptoms relate tothe spinal cord. This is known as post-infective myelitis or transverse myelitis. The patient may have weakness of both legs or all four limbs with decreased sensation. There may be difficulty in urine or stool control.
In measles or chicken-pox the child develops rashes over the skin. After 2 to 4 days the child may develop fever, seizures (convulsions) or may become unconscious. Cerebellar involvement is more common after chicken-pox. The main symptoms are imbalance, unsteadiness. A few other viruses like Epstein-B arr, mycoplasma, cytomegalo virus etc. can also cause ADEM where cerebellar symptoms predominate. This disease is different from viral cerebellitis which results from the direct infection of cerebellum by a virus.
As mentioned earlier, encephalomyelitis may also occur following vaccination for rabies, small-pox etc. Approximately one in 750 people receiving antirabies vaccine is likely to develop this illness and the mortality rate can be as high as 25%. However, HDCV, a newer anti-rabies vaccine is much safer and does not have neurological side effects.
Though the mortality and morbidity tend to be high, recovery can be excellent if the disease is controlled in the initial stages. Usually relapse is uncommon.
High potency steroids should be used to treat ADEM. In more serious patients, plasma exchange or IV gamma globulin; though expensive can be life saving therapies.