Case report highlights dual CNS disease in a young Bichon Frise
Bottom line
A case report in Veterinary Sciences describes a 2-year-old spayed female Bichon Frise with caudal occipital malformation syndrome-associated syringomyelia that continued to deteriorate after a year of medical management. Repeat MRI before surgery showed not only persistent Chiari-like malformation changes, syringomyelia, and ventriculomegaly, but also multifocal intra-axial brain lesions that raised concern for concurrent meningoencephalomyelitis of unknown origin, or MUO. The dog was managed with foramen magnum decompression plus immunosuppressive therapy, and the authors present the case as an example of overlapping structural and inflammatory CNS disease in a single patient. (mdpi.com)
Why it matters: For veterinary professionals, the report is a reminder not to anchor on a known Chiari-like malformation or syringomyelia diagnosis when neurologic signs worsen or shift. In dogs with CM/SM, surgery can improve cerebrospinal fluid obstruction and pain, but recurrence and persistent clinical signs are well recognized, while MUO remains a separate, presumptively immune-mediated condition that often requires corticosteroids with or without additional immunosuppressive drugs. When MRI reveals multifocal intracranial lesions beyond the expected craniocervical abnormalities, clinicians may need to broaden the differential list and consider a combined treatment plan rather than treating the case as decompression alone. (veterinarypartner.vin.com)
What to watch: Whether additional case reports or series clarify how often CM/SM and presumptive MUO coexist, and which patients benefit most from combined neurosurgical and immunosuppressive management. (mdpi.com)
Key facts
- Species
- Dog
- Breed
- Bichon Frise
- Age
- 2 years
- Sex
- Spayed female
- Primary diagnosis
- Caudal occipital malformation syndrome-associated syringomyelia
- Concurrent concern
- Presumptive meningoencephalomyelitis of unknown origin
- Key imaging finding
- Multifocal intra-axial lesions in the thalami, frontal white matter, and medulla
- Treatment
- Foramen magnum decompression plus immunosuppressive therapy
- Clinical course
- Progressive neurologic decline despite 12 months of medical management
A newly highlighted case report in Veterinary Sciences details an uncommon neurology scenario: a young Bichon Frise with caudal occipital malformation syndrome-associated syringomyelia that appeared to have concurrent presumptive meningoencephalomyelitis of unknown origin. After 12 months of medical treatment failed to stop progressive neurologic decline, repeat MRI revealed both the expected structural abnormalities of CM/SM and additional multifocal intra-axial lesions in the thalami, frontal white matter, and medulla, prompting a combined approach of surgical decompression and immunosuppressive therapy. (mdpi.com)
That combination matters because CM/SM and MUO are usually discussed as separate disease processes. CM, also called Chiari-like malformation or historically caudal occipital malformation syndrome, is a skull and craniocervical junction abnormality that disrupts cerebrospinal fluid flow and can lead to syringomyelia and neuropathic pain. MUO, by contrast, is an umbrella term for non-infectious inflammatory CNS disease in dogs, generally diagnosed presumptively based on signalment, MRI, CSF findings, and exclusion of infectious causes. Both conditions are seen disproportionately in small-breed dogs, which can complicate the neurologic workup when imaging findings do not fit neatly into one diagnosis. (pmc.ncbi.nlm.nih.gov)
The case report’s core contribution is clinical, not epidemiologic. It does not establish how common this overlap is, but it shows why serial imaging can change management. In this dog, the pre-surgical MRI reportedly identified lesions that went beyond the classic craniocervical crowding and syrinx pattern expected with CM/SM, supporting suspicion of a second active CNS process. That distinction is important because decompression addresses obstruction at the foramen magnum, while presumptive MUO is typically treated with immunosuppression, most often glucocorticoids alone or paired with drugs such as cytarabine, cyclosporine, azathioprine, or mycophenolate, depending on clinician preference and patient factors. (mdpi.com)
The broader literature helps frame the authors’ decision-making. Reviews of canine CM/SM note that decompressive surgery is often the most direct way to address cerebrospinal fluid flow obstruction, but long-term control can be limited by recurrence, postoperative scarring, or persistent neuropathic pain. A commonly cited summary from Veterinary Partner notes that most dogs in one surgical series initially improved, yet only a minority maintained good quality of life at two years, underscoring that surgery is not always a complete solution. (veterinarypartner.vin.com)
On the inflammatory side, the MUO literature has been evolving away from one-size-fits-all assumptions. A 2023 review of 671 cases found stronger evidence than previously available for corticosteroid monotherapy in some dogs and highlighted ongoing uncertainty around the added benefit of adjunct immunosuppressive drugs. A randomized controlled trial likewise reported no difference in short-term outcomes between corticosteroids alone and corticosteroids plus cytarabine continuous-rate infusion. That doesn’t diminish the rationale for combination therapy in selected severe or complex cases, but it does suggest that treatment plans should be individualized, especially when another structural neurologic disease is present at the same time. (pmc.ncbi.nlm.nih.gov)
Expert-style clinical commentary in the accessible veterinary literature points in the same direction. VIN’s Veterinary Partner describes MUO as an immune-mediated condition most often affecting young to middle-aged small-breed dogs and emphasizes that treatment choices are shaped not just by disease severity, but also by monitoring demands, hospital access, cost, and concurrent disease. In a case like this one, those practical considerations become even more relevant because the patient may need both postoperative neurologic follow-up and long-term immunosuppressive monitoring. (veterinarypartner.vin.com)
Why it matters: For veterinarians, this report is a useful reminder that worsening signs in a dog with an established CM/SM diagnosis should trigger reconsideration of the differential diagnosis, not just escalation of the same treatment pathway. Multifocal brain lesions, progression outside the expected pain-dominant CM/SM pattern, or poor response to standard medical management may justify repeat MRI, CSF analysis when feasible, and a more layered discussion with pet parents about prognosis and therapeutic tradeoffs. The case also reinforces a broader neurology lesson: structural and inflammatory CNS diseases can coexist, and management may need to target both. (mdpi.com)
What to watch: The next step is whether this remains a rare anecdotal overlap or becomes a recognized diagnostic pattern in small-breed neurology patients; additional case series with imaging, CSF data, treatment details, and follow-up would help clinicians decide when combined decompression and immunosuppression is warranted. (mdpi.com)