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Chronic meningitis

The agents responsible for chronic meningitis are listed in Table 2 “Causes of Chronic Meningitis,” below.

Table 2. Causes of Chronic Meningitis (Open Table in a new window)

Brucella species are small gram-negative coccobacilli that cause zoonoses as a result of infection with B abortus, B melitensis, B suis, and B canis. Transmission to humans occurs following direct or indirect exposure to infected animals (eg, sheep, goat, cattle). Direct infection of the CNS occurs in fewer than 5% of cases, with most patients presenting with acute or chronic meningitis. Persons at risk include individuals who had contact with infected animals (eg, sheep, goat, cattle) or their products (eg, intake of unpasteurized milk products). Veterinarians, abattoir workers, and laboratory workers dealing with these animals are also at risk.

M tuberculosis is an acid-fast bacillus that causes a broad range of clinical illnesses that can affect virtually any organ of the body. It is spread through airborne droplet nuclei, and it infects one third of the world's population. Always consider tuberculous meningitis in the differential diagnoses of patients with aseptic meningitis or chronic meningitis syndromes. Involvement of the CNS with tuberculous meningitis is usually caused by rupture of a tubercle into the subarachnoid space.

T pallidum is a slender, tightly coiled spirochete that is usually acquired by sexual contact. Other modes of transmission include direct contact with an active lesion, passage through the placenta, and blood transfusion (rare).

B burgdorferi, a tick-borne spirochete, is the agent of Lyme disease, the most common vector-borne disease in the United States.

C neoformans is an encapsulated, yeast like fungus that is ubiquitous. It has been found in high concentrations in aged pigeon droppings and pigeon nesting places. The 4 serotypes are designated A through D, with the A serotype causing most human infections. The onset may be acute, especially among patients with AIDS. A large number of cases occur in healthy hosts (eg, with no known T-cell defect); however, approximately 50-80% of cases occur in immunocompromised hosts. At particular risk are individuals with defects of T-cell–mediated immunity (eg, those who use steroids, cyclosporine, and other immunosuppressants). Most cases of C neoformans have occurred among individuals with AIDS and among organ transplant recipients. It has also been reported in patients with idiopathic CD-4 lymphopenia, Hodgkin disease, and sarcoidosis.

C immitis is a soil-based, dimorphic fungus that exists in mycelial and yeast (spherule) forms. Persons at risk for coccidioidal meningitis include individuals exposed to the endemic regions (eg, tourists and local populations) and those with immune deficiency (ie, AIDS, organ transplantation).

B dermatitidis is a dimorphic fungus that has been reported to be endemic in North America (eg, Mississippi and Ohio River basins). It has also been isolated from parts of Central America, South America, the Middle East, and India. The natural habitat of B dermatitidis, a dimorphic fungus, is not well defined. Soil that is rich in decaying matter and environments around riverbanks and waterways have been demonstrated to harbor the fungus during outbreaks and are thought to be risk factors for acquiring the infection. Inhalation of the conidia establishes a pulmonary infection. Dissemination may occur in certain individuals (including individuals with underlying immune deficiency [eg, from HIV or pharmaceutical agents] and extremes of age) and may involve the skin, bones and joints, genitourinary tract, and the CNS. Involvement of the CNS occurs in fewer than 5% of cases.

H capsulatum is one of the dimorphic fungi that exist in mycelial and yeast forms. It is usually found in soil.

Candida species are ubiquitous in nature. They are normal commensals in humans and are found in the skin, the gastrointestinal tract, and the female genital tract. The most common species is C albicans, but the incidence of non- albicans candidal infections (eg, C tropicalis) is increasing, including species with antifungal resistance (eg, C krusei, C glabrata).

Involvement of the CNS usually follows hematogenous dissemination. The most important predisposing risk for acquiring disseminated candidal infection appears to be iatrogenic in nature (eg, use of broad-spectrum antibiotics and indwelling devices such as urinary and vascular catheters). AIDS is also considered a predisposing risk factor. Infection may also follow neurosurgical procedures, such as placement of ventricular shunts.

S schenckii is an endemic dimorphic fungus that is often isolated from soil, plants, and plant products. Extracutaneous manifestations may occur, with meningeal sporotrichosis (a rare complication) being the worst complication of S schenckii infections. AIDS is a reported underlying risk factor in many described cases. It is associated with a poor outcome.

Infection with free-living amebas is an infrequent but often life-threatening human illness, even in immunocompetent individuals. N fowleri is the only recognized human pathogenic species of Naegleria, and it is the agent of primary amebic meningoencephalitis (PAM). The parasite has been isolated in lakes, pools, ponds, rivers, tap water, and soil. Infection occurs when swimming or playing in the contaminated water sources (eg, inadequately chlorinated water and sources associated with poor decontamination techniques). The N fowleri amebas invade the CNS through the nasal mucosa and cribriform plate.

PAM occurs in 2 forms. The first form is an acute onset of high fever, photophobia, headache, and change in mental status, similar to bacterial meningitis, occurring within a week following exposure. Because it is acquired through the nasal area, involvement of the olfactory nerves may manifest as abnormal smell sensation. Death occurs in 3 days in patients who are not treated. The second form, the subacute or chronic form, is an insidious onset of low-grade fever, headache, and focal neurologic signs. Duration of illness is weeks to few months.

Acanthamoeba and Balamuthia cause granulomatous amebic encephalitis, which is a subacute opportunistic infection that spreads hematogenously from the primary site of infection (skin or lungs) to the CNS and causes an encephalitis syndrome.

A cantonensis, the rat lungworm, can cause eosinophilic meningitis (pleocytosis with >10% eosinophils) in humans. The adult parasite resides in the lungs of rats. Its eggs hatch and the larval stages are expelled in the feces. The larvae develop in the intermediate host, usually land snails, freshwater prawns, and crabs. Humans acquire the infection by ingesting raw mollusks. G spinigerum, a gastrointestinal parasite of wild and domestic dogs and cats, may cause eosinophilic meningoencephalitis. Humans acquire the infection following ingestion of undercooked infected fish and poultry.

B procyonis is an ascarid parasite that is prevalent in the raccoon populations in the United States and rarely causes human eosinophilic meningoencephalitis. Human infections occur following accidental ingestion of food products contaminated with raccoon feces.

Go to Staphylococcal Meningitis for complete information on this topic.

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