Necrotizing meningoencephalitis in atypical dog breeds: a case series and literature review

Abstract

Background: Canine necrotizing meningoencephalitis (NME) is a fatal, noninfectious inflammatory disease of unknown etiology. NME has been reported only in a small number of dog breeds, which has led to the presumption that it is a breed-restricted disorder.

Hypothesis/objectives: Our objective was to describe histopathologically confirmed NME in dog breeds in which the condition has not been reported previously and to provide preliminary evidence that NME affects a wider spectrum of dog breeds than previously reported.

Animals: Four dogs with NME.

Methods: Archives from 3 institutions and from 1 author's (BS) collection were reviewed to identify histopathologically confirmed cases of NME in breeds in which the disease has not been reported previously. Age, sex, breed, survival from onset of clinical signs, and histopathologic findings were evaluated.

Results: Necrotizing meningoencephalitis was identified in 4 small dog breeds (Papillon, Shih Tzu, Coton de Tulear, and Brussels Griffon). Median age at clinical evaluation was 2.5 years. Histopathologic abnormalities included 2 or more of the following: lymphoplasmacytic or histiocytic meningoencephalitis or encephalitis, moderate-to-severe cerebrocortical necrosis, variable involvement of other anatomic locations within the brain (cerebellum, brainstem), and absence of detectable infectious agents.

Conclusions and clinical importance: Until now, NME has only been described in 5 small dog breeds. We document an additional 4 small breeds previously not shown to develop NME. Our cases further illustrate that NME is not a breed-restricted disorder and should be considered in the differential diagnosis for dogs with signalment and clinical signs consistent with inflammatory brain disease.

Keywords: Autoimmune; Dog; Inflammatory; Intracranial; Seizures.

Figure 1

(A–C) Magnetic resonance images of the brain of a 4‐year‐old Papillon dog with cluster seizures. The patient's right is to the left of each image. Transverse images at the level of the thalamus include T2W (A), precontrast T1W (B), and postcontrast T1W (C) images. There is a mass effect in the right cerebral hemisphere compressing the right lateral ventricle. The ill‐defined lesion in the right cerebral hemisphere, which is hyperintense on T2W (A) and iso‐ or hypointense on precontrast T1W (B). After contrast administration (C), there is mild contrast enhancement of the cerebral parenchyma (white arrowhead) and leptomeninges (black arrowhead).

Figure 2

(A–C) Gross appearance of the brain of Dog 1 (A). The right parietal lobe is swollen with expansion of the white matter and loss of distinction between the gray matter and white matter. Mild hydrocephalus of the lateral ventricles is evident. Marker = 1 cm. Histologic section of the cerebral cortex from Dog 1 (B). The meninges contain an inflammatory infiltrate composed predominantly of lymphocytes and plasma cells. Inflammatory cells also surround cortical blood vessels and extend into the cortical parenchyma. Bar = 400 μm. Higher magnification of a histologic section of the cerebral cortex from Dog 1 (C). Blood vessels are cuffed by lymphocytes, plasma cells, and macrophages. The parenchyma has increased cellularity composed of a mixture of inflammatory cells and glial cells. Numerous necrotic neurons are evident (arrows). Bar = 80 μm.

Figure 3

(A–C) MRI images from Dog 4. A. Precontrast T1‐weighted (A), postcontrast T1‐weighted (B), and T2‐weighted (C) transverse images. Note the marked meningeal and heterogenous parenchymal contrast enhancement as well as marked mass effect. In image C, note the marked hyperintensity of the gray and white matter.

Figure 4

Transverse gross sections of brain from Dog 4. Note the severity of the lesions in the white and gray matter in the frontal lobe and decreasing lesions caudally in the cerebral hemispheres.

Figure 5

Transverse section through the frontal lobe from Dog 4 illustrating segmental but severe meningitis. Hematoxylin‐eosin stain, 1× magnification.

Figure 6

Micrograph of frontal lobe of Dog 4 with marked mononuclear meningitis and underlying polioencephalitis and necrotizing leukoencephalitis. Hematoxylin‐eosin stain, 40× magnification.