Page 309 - Medicine and Surgery

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Chapter 7: Infections of the nervous system 305

Aetiology EEG may be helpful in the diagnosis in over 90% of
This is an uncommon disease, but the most com- cases of HSV-I.
mon cause in the United Kingdom is the herpes sim- In systemic illnesses, serum viral antibody titres can
plex virus (HSV). Other viruses causing encephalopathy be helpful.
include echovirus, coxsackie virus, other members of
the herpesviruses (e.g. varicella zoster, cytomegalovirus,
Management
Epstein–Barr virus). Around the world, arthropod-
In all cases except herpes simplex encephalitis there is
borne viruses cause epidemics and rabies causes an
no effective treatment apart from supportive manage-
almost invariably fatal encephalitis.
ment. Seizures are treated with anticonvulsants. Sus-
pected cases of herpes encephalitis are treated urgently
Pathophysiology
with high dose i.v. acyclovir for 10 days, with up to 5%
HSV tends to cause a temporal encephalitis. Immuno-
of cases relapsing after treatment.
compromised individuals, children, teenagers and the
elderly have an increased risk. Inflammation affects the
meninges and parenchyma causing oedema and hence Prognosis
raised intracranial pressure, diffuse and focal neurolog- Herpes simplex encephalitis has a mortality of 20% de-
ical dysfunction. spite treatment, with poor prognostic factors including
older age, GCS ≤10 at onset of therapy. Persistent neu-
Clinical features rological deficits occur in 50%, particularly memory im-
The main triad of symptoms is headache, fever and al- pairment, personality change, dysphasia and epilepsy.
teredlevel of consciousness. It is an important differen-
tial of bacterial meningitis. In HSV type I encephalitis
nausea, vomiting, and meningism (neck stiffness) affect Miscellaneous infective or
over two-thirds and up to half develop focal symptoms post-infective CNS disorders
and signs, e.g. hemiparesis or dysphasia. Seizures (par-
ticularly temporal lobe seizures) are also a presenting Tetanus
feature.
Definition
Tetanus is a toxin mediated condition causing muscle
Macroscopy/microscopy spasms following a wound infection.
The meninges are hyperaemic, the brain is swollen,
sometimes with evidence of petechial haemorrhage and
necrosis. There is cuffing of blood vessels by mononu- Aetiology
clear cells and viral inclusion bodies may be seen. Clostridium tetani (the causative organism), an anaero-
bic spore forming bacillus, originates from the faeces of
domestic animals. It is found widely in the soil.
Investigations
CT scanning may show areas of oedema (a normal

scan does not exclude the diagnosis, but is indicated Pathophysiology
beforelumbarpuncture(LP)incaseswithalteredcon- The bacteria enter the body at the site of a wound and
sciousness or focal neurological signs). MRI is more if there is an anaerobic environment (e.g. if there is a
sensitive. foreignmaterialpresentinthewound)theyreplicateand
LP – the cerebrospinal fluid commonly shows lym- produce a neurotoxin, tetanospasmin. This toxin travels

phocytosis and raised protein levels. Glucose is un- along the sheaths of peripheral nerves to the CNS and
commonly reduced (a sign of bacterial infection). CSF acts by blocking the release of inhibitory mediators in
may be sent for HSV PCR and antibody tests for HSV, the spinal motor synapses. The result is an overactivity
EBV, CMV and VZV. CSF cultures are usually unhelp- of both the motor system and the sympathetic nervous
ful. system, causing spasms and autonomic dysfunction.