Subacute Sclerosing Panencephalitis
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Direct answer
Subacute sclerosing panencephalitis is a progressive, fatal encephalitis caused by a persistent defective measles virus in the brain, appearing years after an earlier measles infection, usually one acquired in infancy. Its signature is myoclonic jerks with periodic complexes on EEG, and the diagnosis rests on a raised CSF measles antibody titre. No curative treatment exists, so prevention through measles vaccination is the key exam point.
What you must remember
- Cause: a defective, persistent measles virus within neurons, following measles usually acquired before about two years of age.
- Latency: onset comes several years after measles, most often in childhood or adolescence, and the course is progressive.
- Dyken staging: four stages, moving from behavioural decline to myoclonus, then rigidity and akinetic mutism, and finally coma.
- Myoclonus: the hallmark of stage II, with generalised jerks often provoked by stimuli.
- EEG: generalised periodic high-amplitude slow-wave complexes recurring every few seconds.
- CSF: a raised measles antibody titre, out of proportion to serum, with a raised IgG index.
- Treatment: no proven cure; antiepileptics control seizures and myoclonus, and antivirals such as inosine pranobex have limited evidence.
- Prevention: measles vaccination, given as MR under the Universal Immunisation Programme at 9 months and 16 to 24 months.
Stages and workup of the progressive illness
A child with falling school marks and personality change, later followed by jerks and an unsteady gait, is the classic stem. The diagnosis rests on the staged course together with the EEG and CSF findings.
- Stage I, behavioural decline: Personality change, poor school performance and memory loss develop slowly over months.
- Stage II, myoclonus and ataxia: Generalised myoclonic jerks, often provoked by stimuli, appear with ataxia, and periodic EEG complexes are usually present by this stage.
- Stage III, rigidity and akinetic mutism: Dystonia, rigidity, chorea and seizures develop, and the child becomes mute and immobile.
- Stage IV, terminal phase: Coma and a vegetative state set in, and death usually follows within a few years of onset.
- Confirm with CSF and EEG: A raised measles antibody titre in CSF, with a raised IgG index, supports the diagnosis alongside the periodic complexes.
- Exclude mimics: Creutzfeldt-Jakob disease can also produce periodic EEG patterns, so the clinical course and CSF tests must be read together.
Staging is a sequence rather than a fixed timetable, and children move through the stages at different speeds. Examiners reward recognition of the sequence over memorised durations.
Where the exam tries to catch you
SSPE questions usually test the separation from acute measles encephalitis and from other paediatric encephalitides.
- Trap: picking acute measles encephalitis for a child with jerks years after a rash. Correct: SSPE appears years after measles with a progressive course, whereas acute measles encephalitis follows the rash within days.
- Trap: choosing steroids or aciclovir as the cure. Correct: no proven cure exists, so treatment is symptomatic with antiepileptics and supportive care.
- Trap: reading the periodic complexes as hypsarrhythmia. Correct: hypsarrhythmia belongs to infantile spasms, whereas SSPE shows generalised periodic complexes with myoclonus.
- Trap: seeking the diagnosis from MRI alone. Correct: combine the clinical staging, the EEG pattern and the CSF measles antibody titre.
Frequently asked questions
Which EEG finding is characteristic of subacute sclerosing panencephalitis?
Generalised periodic high-amplitude slow-wave complexes, recurring every few seconds, are the characteristic EEG finding in subacute sclerosing panencephalitis. These complexes often appear in the middle stages of the disease. They help separate SSPE from other causes of encephalopathy in children.
What CSF finding supports the diagnosis of subacute sclerosing panencephalitis?
A raised measles antibody titre in the cerebrospinal fluid, out of proportion to the serum titre, supports the diagnosis of subacute sclerosing panencephalitis. A raised IgG index is seen as well. The result is interpreted together with the clinical course and EEG rather than alone.
How long after measles does subacute sclerosing panencephalitis usually appear?
Subacute sclerosing panencephalitis usually appears several years after measles, commonly during childhood or adolescence. The gap is far longer than in acute measles encephalitis, which follows the rash within days. The risk is higher when measles is caught in infancy.
Is there a curative treatment for subacute sclerosing panencephalitis?
No curative treatment for subacute sclerosing panencephalitis is established. Management is supportive, with antiepileptic drugs for seizures and myoclonus, and antiviral agents such as inosine pranobex have been tried with limited evidence. Prevention through measles vaccination is therefore the key message.
Which vaccine prevents subacute sclerosing panencephalitis in India?
Measles-containing vaccination prevents subacute sclerosing panencephalitis by preventing the measles infection that triggers it. Under the Universal Immunisation Programme in India, MR vaccine is given at 9 months and again at 16 to 24 months. Full vaccination lowers the risk of the disease in later childhood.