Obstructive Hydrocephalus and Cardiomyopathy Secondary to Disseminated Protothecosis in a Boxer Dog

Abstract

Canine protothecosis is a rare disease caused by saprophytic unicellular achlorophyllous aerobic algae that are ubiquitous in the environment. We report a novel case of neurological and cardiological manifestations associated with disseminated protothecosis. An adult spayed female Boxer dog was presented with a 1-week history of anorexia, progressive central vestibular signs, and a Grade III/VI systolic heart murmur. Magnetic resonance (MR) imaging revealed obstructive hydrocephalus at the level of the mesencephalic aqueduct, while echocardiography and elevated troponin levels suggested an infiltrative cardiomyopathy. No obvious cause was identified. Cerebrospinal fluid (CSF) collection was not performed due to associated procedural risks. Despite receiving symptomatic treatment and maintaining stability for 3 weeks, the dog eventually suffered cardiorespiratory arrest. Postmortem examination revealed disseminated protothecosis, predominantly affecting the heart and brain. We recommend that in cases where the cause of obstructive hydrocephalus is unclear, especially when CSF collection is not feasible, a comprehensive diagnostic method should be implemented. This includes meticulous investigations to identify infected tissues, followed by sampling and performing cytology/histology and culture tests to confirm the presence of the algal organism. Early diagnosis may allow early treatment, although long-term prognosis remains largely unfavorable due to the absence of effective treatments.

Keywords: MRI; Prototheca; brain; culture; cytology; dog; formalin-fixed paraffin-embedded tissues; heart; histology; panfungal PCR.

Figure 1

Magnetic resonance images. (A) T2-weighted midsagittal plane. (B) T2-weighted transverse plane and (C) T2-weighted FLAIR transverse plane at the level of the aqueduct. (D) T1-weighted midsagittal fat-saturated postcontrast plane. (E) T1-weighted transverse fat-saturated postcontrast plane. The MRI reveals CSF flow obstruction at the level of the aqueduct (green arrow) with no discernible cause. Additionally, transtentorial herniation with flattening of the rostral aspect of the cerebellum and foramen magnum herniation with associated cervical syringomyelia (green star) were observed, likely attributed to increased intracranial pressure. CSF = cerebrospinal fluid; FLAIR = fluid-attenuated inversion recovery; MRI = magnetic resonance imaging.

Figure 2

Postmortem examination, heart. (a) Grossly, the heart is enlarged and discolored white tan. (b) Histologically, the heart is infiltrated and largely replaced by algae and associated necrosis and inflammation. Endosporulation is evident; endospores are occasionally arranged in a radial tripartite configuration (“Mercedes-Benz” endospores; arrow) consistent with Prototheca; hematoxylin and eosin (H&E), 400x; inset-H&E, 600x.

Figure 3

Brain histology. Algae and associated inflammation line and bulge into ventricles; H&E, 20x and 200x (inset).

Figure 4

Brain histology. Algae infiltrate and expand the choroid plexus; H&E, 200x.

Figure 5

Heart histology. (A) Organisms stain positively with Grocott's methenamine silver and (B) periodic acid–Schiff with diastase, compatible with Prototheca infection.