Another case of canine amoebic meningoencephalitis--the challenges of reaching a rapid diagnosis.

A case of granulomatous amoebic meningoencephalitis in a previously healthy, mature, apparently immunocompetent dog, with a history of exposure to stagnant water, is reported. The case presented with ataxia and a tendency to fall to the left side. A computed tomography (CT) showed a ring-enhancing lesion within the cerebellum; an examination of cerebrospinal fluid (CSF) revealed nonspecific mixed-cell pleocytosis. Despite antibiotic and anti-inflammatory therapy, clinical signs progressed rapidly to decerebellate rigidity over 4 days, and the dog was euthanased. Significant post-mortem findings were restricted to the brain, with a localised lytic lesion in the deep cerebellar white matter. Histopathological examination of the brain showed focally extensive cavitation of the white matter and communication of the lesion with the fourth ventricle. The affected area contained structures consistent with amoebae and was infiltrated by neutrophils mixed with lower numbers of macrophages, plasma cells and lymphocytes. The amoebae were identified as Balamuthia mandrillaris, based on specific immunofluorescence detection. Amoebic meningoencephalitis should be considered in dogs with evidence of focal cavitary lesions in the brain, particularly in cases with a history of swimming in stagnant water.