Meningoencephalomyelitis of Unknown Origin in Dogs
Carrie Stefaniak DVM
Meningitis and meningoencephalitis can be caused by both infections (viral, bacterial, fungal, etc.) or non-infectious conditions. The conditions causing non-infectious meningoencephalitis often are collectively referred to as Meningoencephalitis of Unknown Origin (MUO). The most commonly recognized non-infectious meningitis in dogs is known to be steroid-responsive-meningitis. Various subtypes of MUO exist, but these can only be differentiated with a brain biopsy and histopathology, which generally are not performed antemortem in dogs for various reasons. Ongoing research has identified genetic risk in a few dog breeds, but in most cases of MUO, the underlying cause is never identified. MUO conditions can occur in any breed or age of dog, although some subtypes are more prevalent in smaller breed dogs, including the French Bulldog.
Clinical symptoms might include mentation changes, vision changes and blindness, incoordination, neck pain and seizures. Signs of systemic illness also might be noted, including anorexia and fever. Diagnosis is based on cerebrospinal fluid (CSF) analysis and sometimes infectious disease testing (results of which are negative in MUO) and sometimes advance imaging such as MRI.
After the diagnosis of MUO is established, treatment is initiated with immunosuppressive doses of steroids such as prednisone, sometimes in combination with other immunosuppressant medications including azathioprine, cyclosporine, and cytarabine. Prognosis is quite variable, although subtypes of MUO found in French Bulldogs may carry a more guarded prognosis. Initially, many dogs respond to treatment although the disease tends to relapse and progress over months to years after diagnosis.
New research presented at the 2021 AKC CHF conference is looking at the role of the gut microbiome in the treatment of MUO. It is known that MOU is due to abnormal immune function in the brain. We also know that bacteria in the gastrointestinal tract (referred to as the gut microbiome) can impact overall immune system function. The gut microbiome in people with certain immune-mediated diseases and in some dogs with MUO is different than the gut bacteria in unaffected (disease-free) individuals. Preliminary studies in mice demonstrate that altering gut bacteria may reduce severity of some immune-mediated diseases.
Along those lines, AKC CHF studies are supporting research to look into whether an imbalance of a patient’s gut microbiome contributes to the development of MUO in some dogs. Current studies led by scientists at Texas A & M University are looking at supplementation with the gut bacteria Prevotella histicola, in addition to standard immunosuppressant therapies, to treat dogs with MUO. If successful, this could improve treatment and outcomes, and may reduce the need for some immunosuppressive medications.