Differentials
Encephalitis
SIGNS / SYMPTOMS
Abnormal cerebral function, such as altered behaviour and speech or motor disorders, particularly when associated with fever, suggests encephalitis.
INVESTIGATIONS
CT or MRI scans.
Viral meningitis
SIGNS / SYMPTOMS
Relevant exposure history.
No differentiating symptoms and signs.
INVESTIGATIONS
Cerebrospinal fluid (CSF) pressure is usually normal.
CSF WBC count may be normal or 0.01 to 0.5 x 10⁹/L (10 to 500/microlitre) and has a lymphocytic differentiation.
CSF glucose is normal and CSF protein slightly elevated.
Bacterial culture of CSF is negative.
PCR for enteroviruses and herpes viruses may be positive.
Procalcitonin is usually normal.
Drug-induced meningitis
SIGNS / SYMPTOMS
No differentiating symptoms and signs.
History of culprit drug use (e.g., non-steroidal anti-inflammatory drugs, trimethoprim/sulfamethoxazole, amoxicillin, ranitidine).
INVESTIGATIONS
This is a diagnosis of exclusion. Cerebrospinal fluid typically shows a neutrophilic pleocytosis. Symptoms resolve once the drug is stopped.
Tuberculous meningitis
SIGNS / SYMPTOMS
History of contact or residence in endemic area.
Symptoms and signs of pulmonary and extra-neural disease.
INVESTIGATIONS
Cerebrospinal fluid (CSF) smear and culture: sensitivity of smear >50% if repeated drops of CSF sediment dried on a slide and then stained and examined at length. Culture requires large volume for maximum sensitivity.
Skin testing or interferon-gamma-based blood tests for exposure to Mycobacterium tuberculosis supportive, but negative results do not exclude diagnosis of tuberculosis.
Fungal meningitis
SIGNS / SYMPTOMS
Presentation is often insidious with onset of headache and fever over weeks or months. A rash resembling molluscum contagiosum may be present in disseminated cryptococcal disease.
INVESTIGATIONS
Testing cerebrospinal fluid (CSF) for cryptococcal antigen has a sensitivity of almost 100% for cryptococcal meningitis.
In HIV-positive patients the fungal burden is high, leading to high CSF pressures. CSF leukocyte count may be low. India ink stain or cryptococcal antigen is usually positive.
HIV-negative patients have higher CSF leukocyte counts, and India ink stain is positive in only half of cases.
Use of this content is subject to our disclaimer