Page 307 - Medicine and Surgery

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Chapter 7: Infections of the nervous system 303

Aetiology Geography
Avariety of viruses may infect the meninges including Rare in the developed world but a major problem in
enteroviruses, mumps, herpes simplex (see page 400), developing countries.
HIV and Epstein–Barr virus.
Aetiology
Pathophysiology
Mayarise as a complication of miliary tuberculosis or
In viralmeningitis there is a predominantly lymphoid
in primary or post primary infections. In the Western
immune reaction without the formation of pus or ad-
world,TBoccursmostoftenaspartofareactivationpro-
hesions, there is no cerebral oedema unless encephalitis
cess due to immune deficiency, e.g. secondary to ageing,
occurs. alcoholism, HIV or immunosuppression. Tuberculous
meningitis is rare after BCG vaccination.
Clinical features
Patients present with headache usually over 1–2 days,
Pathophysiology
fever, nausea, photophobia, malaise and neck stiffness.
Ifatuberculous focus develops in the brain, meninges or
Rash, upper respiratory symptoms and occasionally di-
skull and ruptures into the subarachnoid space, a hyper-
arrhoeamaybepresent.Theremaybeevidenceofgenital
sensitivity reaction occurs leading to intense inflamma-
ulcers in those with primary HSV-2 infection, but these
tion. This inflammation can directly involve the cranial
are absent in recurrent infections.
nerves,particularlyatthebaseofthebrain;itcanleadtoa
vasculitis which causes strokes; and it can cause commu-
Investigations
nicating hydrocephalus by impeding cerebrospinal fluid
Alumbar puncture should be performed if meningitis is
(CSF) flow and resorption.
suspected. The cerebrospinal fluid (CSF) is usually clear,
with predominant lymphocytes, but early in the illness,
polymorphs may predominate. Clinical features
Culture is possible, but rarely useful clinically as it The onset is usually insidious over days or weeks, al-
takes up to 2 weeks. PCR has been used in some cases to though it may present as an acute illness.
speed diagnosis and hence stopping antibiotics. Stage I: Vague headache, lassitude, anorexia and low-
CT brain is normal. grade fever.
Stage II: Signs of meningism (headache, vomiting, con-
Management fusion, neck stiffness). Focal neurology may develop
If bacterial meningitis is suspected, broad-spectrum an- at this time including cranial nerve signs and hemi-
tibiotics must be given without delay. Analgesia is given paresis.
for headache but no specific treatment is indicated in Stage III: Untreated, the patient becomes comatose.
most forms of viral meningitis. Generally, it is a benign
self limiting condition lasting 4–10 days. Macroscopy/microscopy
The subarachnoid space is filled with a viscous green
exudate, the meninges are thickened and tubercles and
Tuberculous meningitis
chronic inflammation may be seen in the brain and on
Definition the meninges.
Infection of the meninges with Mycobacterium tubercu-
losis. Investigations
Alumbar puncture should be performed and the CSF
Incidence should be stained with Ziehl Nielson stain, and then un-
It is seen in 1% of all cases of TB. dergo prolonged culture. The CSF is typically cloudy,
with a predominance of mononuclear cells (250–500
3
Age lymphocytes/mm )with raised protein and lowered
May occur at any age. glucose. Repeated LP cultures increase the diagnostic