SSPE: a Chronic Encephalitis as a result of Measles
Dr P Tomlin, Paediatric Neurologist, Royal Preston Hospital
What is this?
SSPE stands for subacute sclerosing panencephalitis and refers specifically to an
encephalitis which can rarely follow measles virus infection. It can affect children
and adults when the measles virus persists in the brain.
‘Subacute’ means it has a slow onset and, usually, a gradually emerging progression.
‘Sclerosing’ means that a reaction sets in which damages and scars the brain.
‘Panencephalitis’ means that all areas of the brain can be affected, though the
onset varies from one individual to another.
Unfortunately this is a progressive form of encephalitis without a cure. Though
some treatments have given temporary improvement to some individuals, the disease
process is ultimately overwhelming, being fatal within one year of diagnosis in
the majority of cases.
A ‘Chronic Encephalitis’ is one that has a slow time course such as this.
How common is it?
It is not common. It occurs in about 4 per 100,000 cases of natural measles. It
is more common in developing countries because there is a higher rate of measles
infection in such countries. It is rare in Western countries where there is an effective
measles immunisation programme.
When does it happen?
There is a delay of several years after acute measles infection, before symptoms
are seen. Children catching measles under 2 years of age are more vulnerable to
the condition. Very rarely SSPE comes on more quickly and progresses more rapidly,
particularly if measles is caught by the infant around the time of birth. SSPE can
also be rapid if it appears in a mother during her pregnancy.
What happens?
The brain is affected but as the brain controls the body, the symptoms seen are
physical as well. Two factors may be operating: The measles virus remains in the
brain in a slighty altered form. Also the individual’s immune response to the virus
is abnormal and ineffective in getting rid of it. This sets up a kind of inflammatory
reaction, particularly around small blood vessels in the brain which can be seen
under the microscope. Nerve cells [neurones] in such areas of the brain are damaged
and lost progressively.
How is the child or adult affected?
There are several stages. At first the problems are subtle and hard to spot as an
illness. Usually it begins with a slight change in personality and ability to function
at work, or, for a child to cope with school. This may be a noticeable untidiness
in hand writing for instance, or difficulty in doing ordinary daily tasks, or a
change in the power of expression in conversation. Occasionally brief jerks of the
limbs or loss of muscle control signal fits at this stage.
It is possible in the earlier phase for the brain to become swollen giving signs
and symptoms of raised pressure.
Then within about two months other movement problems emerge. These may be unwanted
uncontrolled movement of limbs which come and go, or a gradual emergence of stiffness
and spastic muscle tone and posture which can be one sided. As these signs emerge
the intellectual deterioration also progresses. Fits can be very troublesome. Vision,
or recognizing what is seen, becomes affected by this stage.
Distressingly for family and carers, dementia and physical disability become severe
and the child, or adult, who is thus affected becomes totally dependent. Finally
problems affecting feeding, swallowing and respiration contribute to the terminal
phase.
How is it diagnosed?
Brain scans may be normal in the early phase, but eventually the sclerosing nature
of the disease shows up as signal change on the magnetic scanner. Before that the
diagnosis is usually made from examining lumbar puncture fluid and measuring the
level of specific measles antibody there and in the blood. This is very high.
The EEG, brain wave pattern can also be suggestive at an early stage, with characteristic
brief complexes of wave forms appearing periodically every few seconds. These are
not fits in themselves, but show a disturbance of the normal electrical pattern
caused by the disease process.
Is there any treatment?
Antiviral agents, such as isoprinosine by mouth; ribavirine intravenously or injected
into the cerebro-spinal fluid [CSF]; Interferon alpha into the CSF, or beta injected
under the skin may have a modifying effect when given as a long-term treatment.
Intravenous immunoglobulins, which are in common usage for immune disorders, have
also been reported to have some benefit. However the disease eventually resumes
its course and no cure has been reported up to this time.
Carbamazepine has proven beneficial for many sufferers in its improvement of seizures.
It is essential that co-ordinated medical and community care are instituted at the
earliest opportunity once the condition is recognised. Much can be done to relieve
discomfort and support nutrition and daily care.
What about research?
There is interest in the problem of disturbed immunity and how it might be helped,
though no clear line of treatment has yet emerged.
Another approach considered is to inhibit or suppress the persisting measles virus
by down-regulating the virus’s RNA [ Ribo Nucleic Acid] – its genetic messaging
system that builds its own proteins. “Interfering RNAs” have been shown to be effective
in research on the measles virus and SSPE measles virus.* [Otaki et al 2006]
Can SSPE be prevented?
This looks very promising through a successful measles vaccination programme with
a good uptake in a population.
There has been a comprehensive review published in 2007* [Campbell et al]. The reviewers
conclude that thorough vaccination programmes do protect the population from SSPE
and indeed have the potential to eliminate SSPE by eliminating measles. There is
no evidence to suggest that the measles vaccine causes SSPE, which is a disease
of the wild virus.
Unfortunately such an aim of elimination has not yet been achieved and the condition
can and does still appear in adults and children. Continuing dedication to immunisation
is essential.
References
Otaki M, Sada K et al. Inhibition of measles virus and SSPE virus by RNA interference.
Antiviral Res 2006;70:105-11
Campbell H, Andrews N et al. Review of the effect of measles vaccination on the
epidemiology of SSPE. Int J Epidemiol. 2007 Dec;36(6):1334-48
Last modified: November 2008