Canine glioma: clinical signs, diagnosis and treatment discussions

Consider glioma without closing the differential

Glioma is an important differential diagnosis for a dog with new seizures. Dogs are typically at least 8 years old when glioma develops, but French bulldogs and Boxers tend to develop these tumors at a younger age. Brachycephalic breeds are affected most often, although any breed can develop glioma. Seizures are a common presenting sign, but age and breed cannot establish the diagnosis. [1] [2] [3]

The neurologic examination helps localize a lesion; it does not establish its cause. The differential diagnosis for seizures includes idiopathic epilepsy, inflammatory brain disease, neoplasia, and reactive seizures caused by metabolic disorders or toxins. [1] [3]

Know when to recommend MRI and CSF analysis

The International Veterinary Epilepsy Task Force recommends brain MRI and routine cerebrospinal fluid analysis, after reactive seizures have been excluded, when seizures begin before 6 months or after 6 years of age, when interictal neurologic abnormalities suggest an intracranial lesion, when status epilepticus or cluster seizures occur, or when a dog with a presumptive diagnosis of idiopathic epilepsy has seizures resistant to a single antiseizure drug titrated to the highest tolerable dose. [1] [3]

Distinguish suspected from confirmed disease

A normal examination between seizures does not exclude a brain tumor. MRI can identify and characterize an intracranial lesion, while histopathologic examination of tumor tissue is needed to confirm glioma. Imaging findings alone should not be presented as a confirmed tumor type or grade. [1] [2]

Clarify treatment goals

Treatment discussions distinguish control of a tumor’s secondary effects from treatment directed at the tumor. Supportive care can include corticosteroids and antiseizure medication; tumor-directed approaches include surgery, radiation therapy and chemotherapy. [1] [2] [4]

Lomustine is a chemotherapy option discussed in the lecture. A retrospective study in dogs with presumptive intracranial glioma reported longer survival with lomustine than with symptomatic care alone. Reported adverse effects were neutropenia in 46% of dogs, anemia in 15% and thrombocytopenia in 15%, with increased ALT in 50% and increased BUN or creatinine in 15%, suggesting potential liver and kidney toxicity. The authors described these toxicities as fairly common but rarely life threatening. The lecture advises monitoring for bone marrow suppression during treatment. These findings describe a study population rather than a guaranteed treatment response. [1] [5]

Discuss survival with its limits

Radiation therapy is another treatment option. Survival estimates depend on the treatment protocol and the population studied, including whether glioma was confirmed in tissue or presumed from imaging. A median survival time summarizes a group; an individual dog may live a shorter or longer time. [1] [4] [6]

Keep emerging therapies in context

Immunotherapy and sonodynamic therapy are being investigated for canine glioma. A retrospective study reported poorer survival in French bulldogs than in Boxers and Boston Terriers receiving the studied immunotherapy protocols. This is a finding about those patients and protocols, rather than proof that every immunotherapy has the same effect across these breeds. Dr. Arnold, who presented the lecture, is the first author of that study. [1] [4]

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