Granulomatous amoebic encephalitis pathophysiology

Overview
Granulomatous amoebic encephalitis is a central nervous system disease caused by certain species of amoeba, especially Balamuthia mandrillaris.

Pathophysiology
Granulomatous amoebic encephalitis is most commonly caused by Acanthamoeba castellanii, A. culbertsoni, A. polyphaga or Balamuthia mandrillaris. It is rarely due to Entamoeba histolytica.

E. histolytica rarely infects the central nervous system and when it does, it tends to cause an abscess with a fulminant clinical course culminating in the patient's death within 12-72 hours (untreated). E. histolytica infection of the brain also tends to occur in patients with a previous diagnosis of E. histolytica infection of the intestines, the liver or the lungs.

Granulomatous amoebic encephalitis is also rarely due to Naegleria fowleri. N. fowleri generally causes acute encephalitis in immunocompetent hosts who go swimming underwater or diving outdoors in fresh water in warm weather.

Chronically ill, debilitated, immunosuppressed or immunodeficient patients tend not to engage in such activities.



The amoebae producing granulomatous encephalitis characteristically produce cysts in the infected tissue whereas E. histolytica and N. fowleri do not.

Multifocal encephalomalacia, edema, necrosis, hemorrhage and sometimes abscess formation are observed. The meninges may be cloudy. Uncal or cerebellar tonsillar herniation may be present. Lesions occur in the cerebral hemispheres, the basal ganglia, the brainstem and the cerebellum. A necrotizing subacute or chronic granulomatous encephalitis with lymphocytes, macrophages and multinucleated giant cells, and variable numbers of organisms are observed microscopically. There may be thrombosis of small blood vessels associated with necrosis and hemorrhage. In AIDS patients, the inflammatory reaction is minimal and composed mainly of CD-68 positive macrophages.

Appearance on Biopsy
A brain biopsy will reveal the presence of infection by pathogenic amoebas. In GAE, these present as general inflammation and sparse granules. On microscopic examination, infiltrates of amoebic cysts and/or trophozoites will be visible.

Cerebrospinal Fluid
The CSF demonstrates a lymphocytic pleocytosis, with mildly elevated protein and normal glucose, but diagnostic organisms are not readily identified. Lumbar puncture is contraindicated if there are signs and symptoms of an increase in intracranial pressure.