Meningoencephalitis: The Difficulty of Definitive Diagnosis

An 8-year old spayed golden retriever was presented for ataxia, dull mentation, cervical pain, inappetence, and an episode of collapse. On examination, the dog was febrile with cervical pain. A CBC revealed a mature neutrophilia, and cerebrospinal fluid (CSF) analysis revealed nondegenerative neutrophilic pleocytosis with no infectious agents. A working diagnosis of steroid-responsive meningitis-arteritis was made; immunosuppressive doses of steroids were administered. After a temporary response, the dog deteriorated and experienced an apparent vestibular episode. 

Magnetic resonance imaging revealed an epidural abscess in the cervical vertebral canal. Drainage of the abscess revealed filamentous, branching organisms. Treatment with clindamycin, ampicillin, cefotaxime, and trimethoprimsulfa was initiated. Oral prednisone was discontinued and IV dexamethasone sodium phosphate was administered at anti-inflammatory doses once a day for 3 days. Enrichment broth cultures of CSF revealed a gram-positive bacterial organism. PCR identified the organism as Actinomyces spp, and cefotaxime and trimethoprim-sulfa were discontinued. After 9 days in the hospital, the patient was discharged with oral amoxicillin, clindamycin, omeprazole, and gabapentin. Oral antibiotics were continued for 8 to 10 weeks. Eight months after drainage of the epidural abscess, the dog was reportedly normal.

Commentary 

A large majority of patients with meningoencephalitis do not have an underlying infectious cause and are treated with immunosuppressive agents.

Excluding an infectious process is vital but challenging, as this case report highlights. A fastidious bacterial organism was ultimately cultured from the spinal fluid but not before the patient deteriorated while receiving prednisone. Infectious causes of meningoencephalitis may include fungal, protozoal, parasitic, and bacterial infections, all of which can be difficult to definitively diagnose. Many organisms have geographical tendencies that can allow a focused list of differentials, but it can be a perilous habit if clinicians limit their list of differentials excessively. Thankfully, further evaluation was performed when the patient deteriorated. This led to an accurate diagnosis, and the dog responded well to appropriate therapy.—Jonathan Bach, DVM, DACVIM, DACVECC