When and why

A lumbar puncture is normally carried out to help diagnose meningitis (usually Cryptococcus) or certain viral infections that can cause neurological problems. It is an essential part of the investigation into the reason for a persistent headache and fever or other problems such as weakness and numbness in the legs. It may also used to help assess the severity of a tumour.

Under a local anaesthetic, a needle is inserted into the base of the spine and a small amount of cerebrospinal fluid removed. This procedure is normally done in an ordinary hospital ward and afterwards the patient is asked to remain lying flat for 4 to 24 hours to reduce the risk of a post-lumbar puncture headache. If swelling of the brain tissue is suspected clinically, then it is essential a brain scan is carried out first to ensure that a lumbar puncture is safe to do.

How it will help

Cryptococcus and other causes of meningitis such as tuberculosis can be readily diagnosed and appropriate treatment started. Viruses which may be implicated in certain neurological problems can also be detected in samples of CSF and help confirm a diagnosis. These include CMV, herpes simplex virus and JC virus. Occasionally a lumbar puncture may be performed to assess the response to treatment for cryptococcal meningitis or to help confirm or exclude a clinical relapse.