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Chapter 30: Infections of the central nervous system

INTRODUCTION

Bacterial meningitis is a medical emergency especially meningococcus meningitis which can cause rapid deterioration of the patient. Consider it if a sudden onset of the classical triad is accompanied by high fever and the signs of a very sick child. Meningococcal meningitis may be accompanied by a petechial rash and septic shock (Waterhouse–Friderichsen syndrome).

ANISHA BAHRA & KATIA CIKUREL, NEUROLOGY, 19991

Infections of the central nervous system cover general conditions such as meningitis and encephalitis and specific organisms such as syphilis and polio. This section is highlighted because the conditions that are difficult to diagnose can have morbid outcomes, especially if the conditions are misdiagnosed. They are representative of classic ‘not-to-be-missed’ conditions.

Key symptoms suggestive of cerebral infection are headache, seizures and altered conscious level.

Meningitis

Meningitis is inflammation of the meninges (pia and arachnoid) and the cerebrospinal fluid (CSF).

The classic triad is:

  • headache

  • photophobia

  • neck stiffness

Other symptoms include malaise, vomiting, fever and drowsiness.

Causes (organisms)1,2

Bacteria

  • Streptococcus pneumoniae, Haemophilus influenzae (especially children), Neisseria meningitides (the big three)

  • Listeria monocytogenes, Mycobacterium tuberculosis, Group B Streptococcus, Strep. agalactiae (common in newborn), Staphylococcus spp., Gram –ve bacilli, such as Escherichia coli, Borrelia burgdorferi, Treponema pallidum

Viruses

  • Enteroviruses (Coxsackie, echovirus, poliovirus) mumps, herpes simplex HSV type 1, 2 or 6, varicella zoster virus, EBV, HIV (primary infection)

Fungi

  • Cryptococcus neoformans or C. gattii

  • Histoplasma capsulatum

Investigations

  • Lumbar puncture (see TABLE 30.1)

  • CT scan

  • Blood culture—all patients with suspected meningitis

  • CSF microculture/PCR (PCR useful even if antibiotics given)

  • Specific serology, e.g. HIV, EBV

Table 30.1CSF findings in meningitis
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Table 30.1 CSF findings in meningitis
  Bacterial (pyogenic) Tuberculosis Viral (aseptic)
CSF appearance Cloudy/pus Opalescent Usually clear
CSF pressure ↑ ↑ ↑ ↑ ↑ or N ↑ or N
Predominant cell Neutrophils Lymphocytes Lymphocytes
Cell count/mm3 100–1000 + 50–1000 10–1000
Glucose ↓ ↓ ↓ ↓ ↓ Normal

Note: If significant delay with these, do not withhold treatment.

Bacterial meningitis2

Bacterial meningitis is basically a childhood infection. Neonates and children aged 6–12 months are at greatest risk. Meningococcal disease can take the form of either meningitis or septicaemia (meningococcaemia) or both. Most cases begin as septicaemia, usually via the nasopharynx. The onset is usually sudden (see CHAPTER 96).

Clinical features (typical)
Infancy

  • Fever, pallor, vomiting ± altered conscious and mental state

  • Lethargy

  • Increasing ...

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