A 6-year-old Boxer was examined because of progressive neurologic signs, with severe hindlimb ataxia and head tilt on presentation. There was no history of diarrhea or vomiting. MRI of the brain revealed multifocal ill-defined T1-enhancing lesions affecting the cerebrum, brainstem, and cervical meninges, without associated mass effect. Meningoencephalitis was considered the most likely diagnosis. Multiple algae were observed on the cytology of the CSF and were most consistent with Prototheca spp. Antiprotozoal treatment was denied by the owners, and 5 weeks after diagnosis, the dog was euthanized due to progression of the neurologic deficits, and a necropsy was performed. Histological changes in the brain were compatible with severe multifocal protothecal meningoencephalitis. The specific Prototheca species was not identified. The gastrointestinal tract was unremarkable on histology. According to this report, Prototheca spp. should be included in the differentials for neurological deficits even in the absence of gastrointestinal signs. 1. Introduction Protothecosis is a rare disease described in many species, caused by a green alga, Prototheca spp. In the cases reported in dogs [1–3], the algae are usually disseminated within the organism, and the affected dogs commonly present large intestine diarrhea. Ocular and neurologic symptoms are also described with protothecosis, but these signs usually appear in a later stage of the disease. To the authors’ knowledge, this is the first case report describing cerebral protothecosis without evidence of dissemination of the alga within the other organs, and more particularly within the gastrointestinal tract. 2. Case Presentation A 6-year-old spayed female Boxer was referred for progressive ataxia of the hindlimbs of 3-week duration. The dog was previously diagnosed with bilateral cranial cruciate ligament rupture, treated surgically 4 months prior to presentation. Physical examination was unremarkable. Neurologic examination revealed a severe hindlimb ataxia, worse on the left, and a left head tilt. Delayed hopping tests were noted in the forelimbs, and the dog fell when hopped in the rear. Crossing over and dragging of the hind feet were also observed. Cranial nerve examination was unremarkable, and there were no conscious proprioceptive deficits. Neurologic examination was consistent with brainstem and/or cerebellar localization. Based on the age, breed, and progressive neurological deficits, the following differentials were considered most likely causes of the clinical findings: neoplasia, such as meningioma
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