Meningitis (Eosinophilic meningitis)

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What is Meningitis?

Meningitis is defined as inflammation of the meninges. Meninges are thin membranes that cover the spinal cord and the brain. There are many causes of meningitis, most commonly infection. Depending on the types of bugs that causes the infection, there will be different immunological cells in the cerebrospinal fluid (CSF - the fluid that surrounds the brain and spinal cord).

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Meningitis

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In eosinophilic meningitis, there is increased number of eosinophils in the CSF. Eosinophil is a type of white blood cell responsible to fight off parasitic infection or to mount an allergic response.

Who gets Meningitis?

The incidence of eosinophilic meningitis is unknown, but it is considered to be a rare disease.

Predisposing Factors

Because most eosinophilic meningitis is caused by parasitic infestation of the meninges, any risk factors that predispose individuals to such exposure will increase the risk of eosinophilic meningitis. Areas of low socioeconomic status and personal hygiene, especially in the tropics increase the risk of infection. This include accidental ingestion of raw seafood, fish and poultry. Ingestion of raw mollusc or food contaminated with raccoon faeces can increase the risk as well.

Progression

The most common cause of eosinophilic meninigitis is parasitic infestation. Several parasites have been identified to cause eosinophilic meninigitis, including:

Angiostrongylus cantonensis
Baylisascaris procyonis
Gnathostoma spinigerum

Another cause of eosinophilic meningitis is fungal infection. The one that causes it is Coccidioidomycosis. Other non-infectious cause is idiopathic hypereosinophilic syndrome. It is a blood disease where the number of eosinophils (a type of white blood cell) rises in the blood without any known causes. There is no apparent parasitic, allergic or other causes found. Other than this, Hodgkin's disease is the commonest cancer associated with eosinophilic CSF (this does not necessarily mean meningitis). Otherwise, drug-induced eosinophilia in CSF can occur as well. These drugs include ibuprofen (a pain-killer) and certain antibiotics.

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