Visiting Vet: Brain inflammation — MUOs

Rapid treatment saves lives.

A dog with brain inflammation may recover if treated with immunosuppressants. —Micah Giszack

Bonito is a handsome chocolate Labrador retriever who has had his share of challenges in life. As a pup, one of his testicles didn’t descend properly, thus requiring a little extra surgery when he was neutered. Next, he began having problems with allergies manifesting as pruritus (the fancy name for itchiness), and recurrent skin and ear infections. His owners tried everything I advised. An elimination diet to rule out food allergies. Desensitization injections to try to lessen his inhalant allergies. Then he developed demodectic mange.

Demodex mites are microscopic parasites that look like tiny fat cigars with stubby legs. They live on the skin and in hair follicles of many mammals, including people. The mites don’t normally cause a problem, as most animals’ immune systems keep the number to a minimum, but sometimes the mites proliferate and create issues. That’s called demodicosis or demodectic mange. Unlike sarcoptic mange, which is caused by a different species of mite, demodectic mange is not particularly pruritic. (You should now know that means itchy.) Symptoms include patchy hair loss, often accompanied by redness, scales, crusting, pimples, greasiness, and secondary bacterial infections.

Juvenile-onset demodicosis is usually mild and may “self-cure,” especially if lesions are small, localized, and few in number, but it is thought that underlying genetic or immunological disorders likely contribute to the condition. Generalized and adult-onset demodicosis are more worrisome, often associated with underlying problems such as diabetes, adrenal gland disorders, or other immunosuppressive illnesses. Treatment has gotten much easier in recent years with the new generations of oral flea and tick products like Nexgard, Bravecto, and the like.

But today’s topic is not mange. Bonito’s demodicosis was mild, localized, and resolved with topical treatment many years ago, and his owners have continued diligently managing his allergies. His weight was a bit harder. Bonito tended to the plump side, and as he aged, had occasional bouts of back pain. So when the now 10-year-old Bonito seemed mopey recently after having roughhoused with a much younger dog, we naturally suspected his back was bothering him. Except his appetite was also off. If Bonito had been a toy poodle or bichon frisé, or some other finicky little dog, this would not have alarmed anyone. But Labrador retrievers? Most Labs will happily eat even with three paws in the grave. When I didn’t find anything dramatically abnormal on his exam to explain his malaise, we decided to run a few tests to be on the safe side.

Every test was normal, except one. Bonito had an abnormally low platelet count. Platelets are blood cells, also known as thrombocytes, that assist with clotting. The in-house machine we use to count platelets can sometimes be inaccurate measuring this particular parameter, so we opted to send samples to our reference laboratory for confirmation. Yup. The result was real. Bonito had thrombocytopenia. We ran more tests. Radiographs. Urinalysis. An anemia PCR panel looking for numerous infectious organisms. While waiting for results, we started medications covering a range of possible diagnoses.

But Bonito’s symptoms were rapidly progressing. By the afternoon he was swaying and having trouble standing up. Now I was seriously concerned, and advised heading right to the specialist off-Island, which they did. Bonito was hospitalized, first at Cape Cod Veterinary Specialists and later transferred to VCA South Shore Veterinary Specialists for a CT scan of his brain.

Meningoencephalitis. A very big word that simply means inflammation of the brain and the membranes that cover the brain and spinal cord. It is a description, not an explanation of the cause. Meningoencephalitis is categorized as either infectious or noninfectious. Infectious causes include viruses like rabies and canine distemper, tick-borne diseases like Lyme, Rocky Mountain spotted fever, and ehrlichiosis, fungal, bacterial, and protozoal infections, even weird migrating worms in the brain, à la RFK Jr. Our initial tests, along with additional blood tests and cerebrospinal fluid analysis done by the specialists, ruled out infectious diseases.

What about noninfectious meningoencephalitis? There are a lot of these, each with equally long, impressive but ultimately unenlightening names. Each affects different sizes, breeds, and ages of dogs. For example, necrotizing meningoencephalitis typically occurs in juvenile small-breed dogs such as Maltese, shih tzus, and Chihuahuas. Steroid-responsive meningitis is more common in young, medium- to large-breed dogs like border collies, springer spaniels, and Bernese mountain dogs. Young male golden retrievers and Rottweilers seem prone to eosinophilic meningoencephalitis. But any breed and any age dog can get meningoencephalitis.

Regardless of the form, clinical signs are similar. Changes in mental status, seizures, blindness, balance disorders, incoordination, fever, loss of appetite, and/or depression. How can we diagnose which kind of noninfectious meningoencephalitis Bonito has? Well, we can’t, really. That would require a brain biopsy — a procedure rarely performed in dogs. Final diagnoses in many cases can only be determined if the animal passes away and the brain is evaluated with post-mortem histopathology. For living patients, neurologists lump these all together as meningoencephalitis of unknown origin (MUOs). The underlying cause for MUOs is thought to be genetic, immune-mediated, or idiopathic (another fancy term that just means “we don’t know”).

Bonito was started on high doses of two immunosuppressants often used successfully to treat MUOs. We were relieved to hear he responded quickly and is feeling better, though not completely back to normal yet. The prognosis for MUO is tricky. We don’t know for sure what is causing it, so we can’t really know for sure if we have “cured” it. We hope Bonito gets back to his old self. Then, with the guidance of his neurologist, we can try to wean him slowly off the medications — or at least to the lowest effective dose. Giving high doses of immunosuppressive drugs like prednisone to Bonito is also tricky. Theoretically, it is contraindicated in dogs with a history of demodectic mange. On the other hand, it may help his allergy symptoms, and manage his pruritus but, for now, it is essential for the treatment of his meningoencephalitis.