The most common are the fungus Cryptococcus, cytomegalovirus, the virus that causes AIDS, and the bacteria that cause tuberculosis, syphilis, and Lyme disease. Some noninfectious diseases such as sarcoidosis and some cancers can irritate the meninges, producing chronic meningitis. Of the noninfectious causes, invasion of the meninges from lymphomas and leukemias is most common. Some drugs used to treat cancer, others used in organ transplants, and even such nonsteroidal anti-inflammatory drugs as ibuprofen also can inflame the meninges. The symptoms of chronic meningitis are similar to those of bacterial meningitis, but the illness develops more slowly, generally over weeks rather than days.
Fever is often less severe than in bacterial meningitis.
The diagnosis of chronic meningitis is suspected on the basis of its symptoms. However, bacterial meningitis that's been modified but not eliminated by a partial course of antibiotics and brain tumors or abscesses may be mistaken for chronic meningitis. Infectious organisms may be visible under the microscope. The cerebrospinal fluid is always cultured to identify the specific organism. Additional tests may be ordered to check for tuberculosis or syphilis and for certain fungi and viruses.