Concurrent Caudal Occipital Malformation Syndrome-Associated Syringomyelia and Presumptive Meningoencephalomyelitis of Unknown Origin Managed with Combined Surgical Decompression and Immunosuppressive Therapy in a Dog.

A 2-year-old spayed female Bichon Frise presented with progressive neurologic deterioration despite 12 months of medical management for caudal occipital malformation syndrome (CM)-associated syringomyelia (SM) and ventriculomegaly. Repeat magnetic resonance imaging (MRI) performed prior to surgical intervention demonstrated persistent CM-associated structural abnormalities together with multifocal intra-axial lesions involving the bilateral thalami, frontal white matter, and medulla that were considered most compatible with a presumptive inflammatory meningoencephalitic process, with MUO regarded as the leading differential diagnosis. Combined surgical decompression and immunosuppressive therapy using leflunomide and mycophenolate mofetil were subsequently initiated. Progressive clinical improvement followed by long-term neurological stability was observed during the approximately 2-year follow-up period. However, because both interventions were initiated concurrently, the relative contribution of each treatment to the observed clinical outcome could not be determined. No recurrence or progression of neurological signs was observed during the approximately 2-year follow-up period. This case highlights the importance of repeat MRI evaluation in neurologic patients exhibiting progressive deterioration despite previous treatment, even when an established structural diagnosis is present. Recognition of MRI findings suggestive of concurrent inflammatory disease may substantially influence diagnostic interpretation and therapeutic decision-making in selected patients.