Neurology Case Study: Sammy, 4-Year Old Boston Terrier
By Dr. Michael Podell
Sammy is a 4 year-old male neutered Boston terrier that presented for evaluation of a recent history of new onset epileptic seizures starting the prior week. The owners had recently traveled from their winter home in Las Vegas and were visiting Chicago for the summer. The trip was uneventful until Sammy had his first seizure the night arriving in Chicago (what a welcome!). He then had 3 additional seizures over the next 2 days and was started on phenobarbital prior to evaluation.
The neurologic examination was normal with the exception of a somewhat lethargic state. A complete blood count, chemistry panel, thoracic radiographs and abdominal ultrasound were all normal. MRI scan of the brain revealed a left frontal lobe fluid-filled cystic mass that contained an intra-cystic, rim-enhancing mass. (Figure 1)
Figure 1. MRI scan of brain with T2W axial (left) and T1W with contrast coronal (right) images demonstrating a focal, left frontal lobe tumor that has a fluid-filled cyst with an intra-cystic rim-enhancing mass.
Therapeutic options were discussed to include fungal titers, surgical excision and biopsy, or palliative care. As part of the decision-making process, the owners were informed that if an OLG was diagnosed, then additional therapy would be recommended to include radiation therapy and possible chemotherapy. The long-term prognosis for oligodendroglioma in people has markedly improved over the past decade with the advent of an oral chemotherapy agent, temozolomide (TMZ). The 4 year survival in patients with low grade OLG was recently found to range between 78 to 100 percentage, with better survival in patients without combined 1p/19q chromosomal deletion and methylated MGMT (Choi et al, 2010). Temozolomide is a cytotoxic alkylating chemotherapy agent with high brain penetration and good tolerability and was well-tolerated in dogs treated for lymphoma (Dervisis et al, 2007). The cytotoxicity is due to inhibition of DNA replication via blockade of guinine-rich DNA sites. No published data was available to present to the owner regarding the use of TMZ for canine OLG treatment. After careful consideration, the owners elected for surgery 2 days after the first evaluation.
A left rostro-lateral craniectomy was performed to expose the left frontal and parietal cortex. The tumor was identified by non-traumatic dissection through the cortical gray matter to reveal an encapsulated, cystic lesion. The cyst fluid, cyst wall and intra-cystic mass were excised and biopsied. The resection cavity was then lined with a hemostatic mesh (Surgicel®) and filled with Gel-foam®. A synthetic, dural graft matrix (Duragen®) was placed over the surgical site prior to closure. Sammy recovered well, and was discharged 4 days post-operatively.
A diagnosis of low-grade oligodendroglioma was obtained from the biopsy. To mimic the potential for long-term survival as reported in people with a similar diagnosis, a treatment plan was established consisting of fractionated radiation therapy with 45 gray total dose over 15 treatments. Supplement treatment include prednisone at 1 mg/kg/day and levetiracetam (Keppra®) at 20 mg/kg tid. Following the radiation therapy, temozolomide was initiated at 150 mg/m2 once daily for 5 days and repeated in 28 days. Each dose was given at night and preceded by an oral anti-emetic dose of maropitant citrate (Cerenia®) at dinner. A CBC and chemistry panel was performed monthly. Three months into the therapy, the dose was reduced to 100 mg/m2 due to the onset of leucopenia and thrombocytopenia. Within 2 months, the laboratory testing returned to normal.
Sammy was re-evaluated one year after surgery for examination and MRI brain scan. He appeared completely normal and had not developed any further seizures or drug-related toxicity. A follow-up MRI scan revealed absence of any evidence of cyst or tumor. (Figure 2) The temozolomide was continued for an additional 3 months and then discontinued. To date, four years later, Sammy is doing very well, living seizure-free on levetiracetam as the only treatment. We look forward to seeing him back in Chicago this summer!
Choi KY, et al. Prognosis of oligodendroglioma tumor with ring enhancement showing central necrotic portion. J Neurooncol. 2010; August 25, online edition. DOI: 10.1007/s11060-010-0353-zOnline First™
