Necrotizing pyogranulomatous encephalitis in a cat

Necrotizing pyogranulomatous encephalitis in a cat

Whats your diagnosis #4

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History: An 8 month old castrated male  DSH cat with weak PLR’s, slow menace,  circling to the left, and then progressed to ataxia, and he had a distendedbladder.

An 8 month old castrated male  DSH cat with weak PLR’s, slow menace,  circling to the left, and then progressed to ataxia, and he had a distended

Gross findings: No gross abnormalities


Brain:  There are multifocal to coalescing areas of spongiosis,
necrosis and edema in both grey and white matter with large numbers of
lymphocytes, macrophages, and variable numbers of neutrophils and
multinucleated giant cells.  Cellular infiltrates center mostly
around blood vessels within the cerebrum and brainstem.  There are
numerous blood vessels surrounded by large numbers of lymphocytes
and plasma cells with some histiocytic cells.

Brain: Perivascular histiocytic infiltrates with few neutrophils

Brain: Coalescing perivascular and parenchymal histiocytes with neutrophils, lymphocytes, and plasma cells

Brain: Perivascular lymphocytic cuffing

Brain: There are many multinucleated cells within the inflammatory infiltrates

Morphologic Diagnosis:

Brain: Granulomatous and necrotizing encephalitis, multifocal to
coalescing, severe

Differential diagnoses:

Rabies-                               No negri bodies, and inflammation not typical.
FIP-                                     Negative on IHC
FIV-                                     Negative PCR
FeLV-                                  Negative PCR
Fungus-                              No yeast or hyphae seen on H&E, GMS, or PAS stains
Bartonella henselae-    No bacteria seen with Warthin Starry silver stain, Gram                                               stain, Giemsa or H&E
Amoebic encephalitis- No protozoa seen with PAS stain
Toxoplasma-                    No protozoa seen with PAS stain
HPAI-                                   Negative PCR

Brain: There were multiple=

There are many large cells with small dark nuclear fragments

We interpreted the above photo to represent an apoptotic giant cell. Below, a paper from Vet Path (Vet. Pathol. 33:699-703 (1996)) describes a cat infected with FIV having cells with large hyperchromatic nuclei or bizarre multinucleated cells.  The similarity to the above photo made us think that FIV was a possibility in this case.


We sent a piece of the brain for an array of PCR tests that included FIV, FeLV, Influenza, Calicivirus, Coronavirus, and many others.  The only encephalitic virus not accounted for was Borna virus, which is unlikely but still a possibility.   The lesion is very atypical for viral infections, but we wanted to rule out FeLV and  FIV infections, since there have been reports of granulomatous encephalitis with HIV in humans and  FIV infected cats (Vet Pathol. 1996 Nov;33(6):699-703).  When the PCR test results came back we were cautioned that there is a chance of false negatives for the FeLV and FIV results since the specimen didn’t arrive frozen.  There is still the possibility of FeLV anfd FIV infection in this cat.   FIP can cause similar lesions in cats, but I have not seen them with so many multinucleated cells, and our IHC works very well.  Of course other possibilities include an idiopathic or immune mediated condition similar to canine Granulomatous Meningoencephalitis, but we are not prepared to make that diagnosis in this case.

So, we do not have a confirmed diagnosis in this case.  If anyone has any other ideas please post a comment.

Encephalitis in cats:

Neuropathology of Italian Cats in Feline Spongiform Encephalopathy Surveillance. Vet Pathol September 2008 45: 626633. – Neoplasia (21.8%), toxic-metabolic encephalopathy (18.2%), granulomatous encephalitis (15.5%), suppurative encephalitis (4.6%), trauma (3.6%), circulatory disorders (3.6%), degeneration (2.7%), nonsuppurative encephalitis (2.7%), and neuromuscular diseases (1.8%)

A Retrospective Study of 286 Cases of Neurological Disorders of the Cat. Journal of Comparative Pathology Volume 131, Issues 2-3 pp 112-120; 2004– 47/92 cats had feline infectious peritonitis (FIP) virus. Of the 45 remaining cases (i.e., non-FIP cats) eight had protozoal tissue cysts (presumed but not confirmed to represent toxoplasmosis; and one had cryptococcosis,  One cat with FIP also had toxocara infection.

Feline leukemia virus in a captive bobcat. Journal of Wildlife Diseases, 37(1), 2001, pp. 194-200. Multifocal non-suppurative encephalitis, diffuse interstitial pneumonia, multifocal hepatocellular necrosis, non-suppurative peritonitis, and lymphoid depletion.

Encephalitis Associated with Giant Cells in a Cat with Naturally Occurring Feline Immunodeficiency Virus Infection Demonstrated by In Situ Hybridization. Vet Pathol November 1996 33: 699703. Perivascular lymphocytic cuffing, gliosis, and white matter vacuolation were most severe in the cerebrum,affecting the white matter and the deep laminae of the grey matter. Gemistocytes were prominent, and many bizarre cells with large, sometimes multinucleate, hyperchromatic nuclei were evident.

About Brian

Anatomic Pathologist, VetPath Services, Stone Ridge, NY- musculoskeletal, oral/dental, and sinonasal diseases
This entry was posted in Necropsy Cases and tagged , . Bookmark the permalink.

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