When to do a lumbar puncture: if you suspect meningitis, unless there is a specific contraindication. (Diagnosis).

Lumbar puncture has long been a key investigation. The "classical signs" of meningitis are often absent in infants in the first year of life. Lumbar puncture is thus advocated for any infant who is drowsy or ill, without awaiting the development of meningeal signs. (1) Concerns about the perceived dangers of lumbar puncture (2) and a suggestion that it has little diagnostic value in meningococcal disease (3) have led to fewer lumbar punctures being performed. (4) Some experts have expressed concerns that not enough lumbar punctures are being performed, since the consequences of missing meningitis may be disastrous. (5) A review of the indications for lumbar puncture is thus timely, and papers in this issue by McMaster and colleagues (6) and Carroll and Brookfield (7) contribute to this debate.

CRITICAL QUESTIONS

Critical questions include:

* What are the benefits of lumbar puncture in suspected meningitis?

* What are the contraindications to lumbar puncture?

* How is meningitis diagnosed and treated if an early lumbar puncture is not done?

* Should lumbar puncture be performed after a febrile convulsion?

WHAT ARE THE BENEFITS OF LUMBAR PUNCTURE IN SUSPECTED MENINGITIS?

In most cases lumbar puncture confirms or excludes bacterial meningitis. It is rare for microscopy of cerebrospinal fluid obtained at lumbar puncture to be normal, and a pathogen to be grown later. This occurs most often in meningococcal meningitis (up to 8%). (4) These children have clinical signs of meningitis or septicaemia (rash) and should receive antibiotics in spite of a "normal" cerebrospinal fluid. Children rarely develop meningitis some hours after a normal lumbar puncture. The suggestion that the lumbar puncture itself performed during bacteraemia may cause meningitis remains controversial and unproven. (8)

Initial Gram staining of cerebrospinal fluid reveals an organism in 68-80% of cases of meningitis, (9) allowing appropriate choice of antibiotics. Subsequent culture gives information on antibiotic resistance, which is especially important in areas where antibiotic resistant pneumococci are prevalent. (6)

Obtaining cerebrospinal fluid also allows identification of uncommon pathogens, such as mycobacteria and fungi. This is particularly important in children with immunodeficiency or on an intensive care unit.

Enteroviral meningitis can be …