· Meningitis: inflammation of the Dura mater, arachnoid +/- pia mater
· Myelitis: inflammation of the spinal cord parenchyma
· Encephalitis: inflammation of the brain parenchyma
· Radiculitis: inflammation of the nerve roots
· Neuritis: inflammation of the peripheral nerve
Fine, I can say it now, but what is it?
Meningoencephalomyelitis is a term which refers to inflammation of the meninges and neuroparenchyma of the brain and spinal cord. There are two forms of meningoencephalomyelitis: 1) infectious and 2) inflammatory non-infectious. Infectious causes include viral (rabies, distemper, feline corona virus), bacterial (direct transmission or hematogenous), protozoal (Neospora, Toxoplasma), fungal (variable depending on the area of the country), and rickettsial (Ehrlichia and Rocky Mountain Spotted Fever). Inflammatory MEM is more common in many areas of the US and is suspected to be an immune-mediated disorder. Inflammatory MEM can be more specifically characterized with histopathology as granulomatous(GME), necrotizing (NME), necrotizing leukoencephalomyelitis (NLE), eosinophilic meningoencephalitis (EME), or steroid responsive meningitis-arteritis (SRMA). Without histopathology, we call immune mediated meningoencephalitis "Meningoencephalitis of Unknown Origin" or MUO.
How is it diagnosed?
Granger and Smith proposed the following criteria for a diagnosis of MUO:
1) multifocal neuroanatomic lesion localization;
2) age >6 months;
3) intraaxial hyperintense lesions on T2-weighted MRI;
4) pleocytosis with >50% mononuclear cells and increased protein concentration in CSF; and
5) negative testing for geographic-specific infectious diseases.
This approach does not cover all possible presentations of MUO, but will help you diagnose the majority of cases. The diagnostic tests are recommended for several reasons: 1) the combination of MRI and CSF analysis improves the chances of obtaining a positive diagnosis, 2) for cases of intracranial disease, it is important to know if there is evidence of brain herniation prior to performing a CSF collection and 3) while infectious etiologies are much less common, immunosuppressing a patient with infectious meningitis can increase mortality.
What if I cannot confirm the diagnosis, but I highly suspect it. How should I manage this case?
Given the high likelihood of immune mediated meningoencephalitis, I will often recommend immunosuppressive doses of prednisone concurrently with anti-infective drugs reflective of the area of country I am working. For Wisconsin, this means I add Clindamycin. When I was in Illinois I added Clindamycin or Sulfa drugs AND doxycycline. Regardless the most important part of this treatment plan is the conversation with the owner saying that we are treating without a diagnosis and therefore the dog may improve, worsen or remain unchanged and we still won't know what is actually wrong. Prednisone treatment is not a diagnostic test for the brain!
A note about consults, for those of you in my consult radius....
I am doing 99% telemedicine at this point to Harbor at Home for COVID-19. Telemedicine for me means that I consult over video with veterinarians only, and the patient. I am happy to call the client on the phone after evaluating the patient with you "electronically" but I do not consult with clients and their pets over video.
If a live consult is needed I respectfully request that hospitals do not invite owners into the consult, and that any staff member I interact with has mask and gloves on during our consultation. Whenever safe I perform the exam outside in a parking lot, enclosed "potty area" or other safe region OUTSIDE of the hospital space. The hands-on portion is abridged to minimize invasion of personal space that often occurs during neurology consults. We all need to care for pets and I wish to continue to support you to the best of my ability within the reality that we are faced with right now!
Stay safe, stay healthy, and keep those (virtual) consults rolling!