Aseptic meningitis

Aseptic meningitis is a condition in which the layers lining of the brain, or meninges, become inflamed and a bacterial or viral source cannot be detected. Meningitis is diagnosed when cerebrospinal fluid (CSF), obtained via lumbar puncture, reveals an increase in the number of leukocytes present (normal being fewer than five visible per microscopic high power field). more...

The term aseptic is frequently a misnomer, implying a lack of infection. On the contrary, many cases of aseptic meningitis represent infection with viruses or mycobacteria that cannot be detected with routine methods. While the advent of polymerase chain reaction has increased the ability of clinicians to detect viruses such as enterovirus, cytomegalovirus, and herpes virus in the CSF, many viruses can still escape detection. Additionally, mycobacteria frequently require special stains and culture methods that make their detection difficult. When CSF findings are consistent with meningitis, and microbiologic testing is unrevealing, clinicians typically assign the diagnosis of aseptic meningitis—making it a relative diagnosis of exclusion.

Aseptic meningitis can result from non-infectious causes; it is a relatively infrequent side effect of medications, and can be an early finding in autoimmune disease.

Read more at Wikipedia.org