ABSTRACT
Meningoencephalitis of unknown origin (MUO) is an umbrella term for a variety of subtypes of meningoencephalitis of dogs and cats with no identifiable infectious agent. In dogs, granulomatous meningoencephalitis (GME), necrotizing meningoencephalitis (NME), and necrotizing leukoencephalitis (NLE) are the most commonly reported subtypes. However, sporadically there are reports about other subtypes such as greyhound encephalitis or eosinophilic meningoencephalitis. The following case series presents three dogs with peracute to acute progressive signs of encephalopathy. The magnetic resonance imaging (MRI) of two dogs (post mortem n = 1/2) showed severe, diffuse swelling of the cortical gray matter with increased signal intensity in T2weighted (w) and fluid-attenuated inversion recovery (FLAIR) and decreased signal intensity in T1w. Additionally, focal to multifocal areas with signal void in both dogs and caudal transforaminal herniation of the cerebellum in one dog was observed. Post mortem histopathological examination revealed lympho-histiocytic encephalitis and central nervous system (CNS) vasculitis in all dogs. No infectious agents were detectable by histopathology (hematoxylin and eosin stain), periodic acid-Schiff reaction (PAS), Ziehl-Neelsen stain and immunohistochemistry for Canine adenovirus-1, Parvovirus, Listeria monocytogenes, Parainfluenzavirus, Toxoplasma gondii, Herpes-suis virus, Pan-Morbillivirus, Tick born encephalitis virus, Severe acute respiratory syndrome coronavirus (SARS-CoV) 2. Furthermore, two dogs were tested negative for rabies virus. To the best of the authors' knowledge, this is the first report of a lympho-histiocytic encephalitis with CNS vasculitis with no identifiable infectious agent. It is suggested to consider this as an additional subtype of MUO with severe clinical signs.
ABSTRACT
Meningoencephalomyelitis of unknown origin (MUO) is an umbrella term describing inflammatory changes of the central nervous system (CNS) with suspected non-infectious etiology. Diagnosis of MUO mostly remains presumed in a clinical setting. Histopathological and immunohistochemical examination of CNS tissue represent additional tools for detection of inflammation and the exclusion of specific infectious agents. While MUO is well-described in canine patients, only little is known about MUO in cats. Previous reports of feline MUO involve either clinical findings or histopathological examination but not both. The present case series is the first report describing both clinical and histopathological findings of feline MUO: Four cats (age: 1.7-17.8 years) showed acute to chronic progressive neurological signs of encephalopathy or myelopathy. Three cats had extraneural signs (hyperthermia, weight loss, hyporexia, leukocytosis). Magnetic resonance imaging (MRI) showed multifocal intraparenchymal lesions in forebrain, brainstem or spinal cord with homogenous contrast enhancement (2/2). Cerebrospinal fluid (CSF) examination was normal or displayed albuminocytologic dissociation. Histopathology revealed a multifocal, lympho-histiocytic meningoencephalitis in three cases and a lympho-histiocytic myelitis in one case. Immunohistochemistry for feline parvovirus, feline coronavirus, feline herpesvirus, tick borne encephalitis virus, Borna disease virus, morbillivirus, rabies virus, suid herpesvirus-1, and Toxoplasma gondii were negative in all cases. ONE SENTENCE SUMMARY: This case series is the first one reporting both clinical and histopathological findings in cats with MUO. Feline MUO incorporates heterogeneous subtypes of sterile CNS inflammation.