Pug encephalitis, termed necrotizing meningoencephalitis (NME), is a common cause of CNS inflammation in Pug, Maltese, Chihuahua, Shih Tzu and other small breed dogs. The typical presentation is a dog less than 4 years old with acute, progressive, multifocal CNS signs. (However, meningoencephalitis is the great pretender so it may present in ANY age, breed, sex, and with neurologic examination findings!) Many Pugs are reported to be resistant to immune suppression, however this is not a global truth. On histopathology, areas of necrosis are identified, along with infiltration of inflammatory cells which leads to the term necrotizing meningoencephalitis. Antemortem, a diagnosis cannot be rendered. MRI and CSF changes would lead a practitioner to a diagnosis of meningoencephalitis but without histopathology (biopsy or necropsy) the dog would be diagnosed with meningoencephalitis of unknown etiology (MUE). MUE includes the necrotizing meningoencephalitis and granulomatous meningoencpehalitis thus it is not a histopathologic diagnosis but a clinical one.
What if we could detect NME earlier?
Researchers recently published a study with this question in mind. They evaluated 36 pug dogs that were deemed clinical normally by their owners. Genetic studies were performed; 5 homozygous/high risk, 19 heterozygous/medium risk and 12 low genetic risk (previously published data about genetic link) dogs were included. They then performed 2, sequential neurologic examinations on these dogs at least 4-6 weeks apart. Dogs that were considered repeatably abnormal subsequently underwent MRI (spine, brain, or both) and had a CSF analysis performed.
Results of the study
Dogs considered low risk had 0 repeatable abnormalities on neurologic examination. Eight of the 36 "at risk" pugs had repeatable abnormalities. Abnormalities included back pain, menace deficits, ataxia and paw replacement deficits (1 or more). The only statistically significant finding was multifocal spinal pain. The 8 dogs underwent imaging and mild brain abnormalities were noted in all dogs with variable severity. CSF changes were noted in 3 of the 8 dogs.
What is the actionable result of this study?
The take away here is that the MRI was more sensitive to detecting "pre clinical" NME than CSF analysis. Is this actually "pre clinical" if the dogs had repeatable neurologic examination abnormalities? I argue perhaps not, perhaps they were "undetected" by clients rather than preclinical. That said, we don't subject dogs to annual neurologic exams without reason so perhaps this is a reasonable way to conduct the study. (Maybe we should??) I always ask myself: what I would do with the information gained when I suggest a test or procedure? In this case, would I treat this dog with "pre clinical" MRI changes or would we wait to see if this develops into progressive disease? I don't know the answer to this question and they didn't pursue treatment in this study so I don't have an objective answer for you. For me, these types of studies will help us help dogs considered genetic "at risk" for NME. Perhaps we identify treatment earlier? Perhaps we find out that there is a specific environmental trigger? Perhaps you learned that there is a genetic "risk" for pugs. Have a pug patient or pet that you think should be genetic tested? Here is the link: http://www.vgl.ucdavis.edu/services/dog.php
The big question is - at risk does NOT equate to disease - so what do we do with the information??
Thanks for reading today. I really enjoyed reading this study and hope you enjoyed my summary.
Have a great week and keep those consults rolling. My kids will be in and out of different camps this summer so my schedule will be changing week-by-week. As always, please reach out if you cannot find a suitable time for your patient using the online scheduler and I will do my best to find timely spot!