Could This Be a Osteosarcoma? - Reader Question and Response

by Anonymous

My Rottweiler is 5 years and 8 months old. In early September he developed a slight limp in his front left arm. Six weeks yesterday, he had a CT scan as The vet at first said he thought it may be arthritis or elbow dysplasia. We asked him if he thought it may be osteosarcoma but he said no as that is so painful, and usually he would be able to see and feel it, neither of which he could at the time. After the scan the vet advised he was of the belief it was osteosarcoma in his front left leg, though a very tiny chance it may be a bone infection but unlikely. He said the only way to be sure was a biopsy which he would not recommend due to the fracture risk. He did say there was one nodule on his chest, but that could be benign. He said even the blood tests indicated a healthy dog. We lost two previous dogs to osteosarcoma so we know progressive it is. He advised that although it was very early on, amputation would not be advisable due to his arthritis.

After a couple of days we did request if he could be treated for a bone infection, just for our peace of mind so that later we did not regret not trying everything we could. The vet agreed and issued a three week course of antibiotics (Clinacin). He stayed the same for two weeks (despite us expecting a decline) but then after two weeks he improved, his limp was mostly gone and he was back to running around/playing/barking as normal. After the three week course finished we called our vet, and he said he was expecting us to call to say it was time to put him to sleep, but we said he had improved. He then said he would recommend a further CT scan, as if it is a one infection then he would need more antibiotics. We agreed to this course of action. His scan was not until over a week later (Wednesday 18th October). They did not do any further blood tests When we picked him up we were advised by the assistant that the results would take a few days, but may be in within 48 hours. From 2 days after, we chased the vet each day for results, but was continually told the report was not in but that we would receive a call from the vet later. Only yesterday, after again chasing, did we receive a call back from the vet who said the results were on file and we should have been called, but there seemed to be a mild progression and they are all of the opinion it is osteosarcoma and not a bone infection. They have not given an indication of how long he has left, as they said though a mild progression at the moment it may speed up. It has now been six weeks and a day since his first scan.

We are surprised, as everything we have read indicates Osteosarcoma is a very fast progressing disease, and given that he improved after a course of antibiotics, he is still playing/eating as normal (in fact he put on 2kg in between the two scans) and his leg still doesn't appear to be sensitive - he lets us touch it and does not react; we cannot see a mass still. Although we bought strong pain killers at the time of his diagnosis (amantadine and gabapentin) we still have not given these to him as he appears to not need them; he does however have metacam each evening after his dinner which the vet advised due to his arthritis.

Can osteosarcoma look similar to osteoma on a ct scan? We are surprised as we lost our previous two dogs to osteosarcoma and we had to put them to sleep very shortly after their diagnosis.

Thoughts From Our Editor on Osteosarcoma

I'm really sorry to hear about the difficult situation you're facing with your Rottweiler. Based on the comprehensive medical history and procedures you've described, here's what I can offer in terms of possible explanations and recommendations:

Osteosarcoma: Given your vet's strong suspicion based on CT scans and medical history, this remains the most likely diagnosis. Osteosarcomas are usually aggressive, but they can present differently in each case. For some dogs, pain or disability manifests later in the disease progression.

Action: If you haven't already, consult a veterinary oncologist for a second opinion and potential treatment options like chemotherapy, if amputation is not an option due to arthritis.

Bone Infection: The improvement with antibiotics suggests the possibility of a bone infection. However, this is less likely given that the CT scan showed progression.
Action: If you want to rule out infection definitively, discuss more specific diagnostic tests with your vet, such as a bone culture, although the risks must be weighed carefully.
Osteoma or Other Benign Lesions: While osteosarcoma is generally easier to distinguish from benign tumors like osteoma on a CT scan, there are instances where they can appear similar. However, this is less common.

Action: If you wish to explore this avenue further, a second opinion from a board-certified veterinary radiologist may be helpful. Note that biopsy is usually the gold standard for differentiation but carries a risk of fracture, as your vet mentioned.
Arthritis/Elbow Dysplasia: Since your dog has a history of arthritis and was initially suspected to have elbow dysplasia, there's a chance that some of his symptoms are attributable to these conditions.

Action: Continue with the Metacam as advised by your vet for the arthritis. Reassess the need for additional pain management like gabapentin or amantadine based on his comfort levels.

It's understandable that you're puzzled by the lack of more aggressive symptoms given your past experience with osteosarcoma in other pets. While literature does suggest that osteosarcoma is typically aggressive and painful (Source: VCA Hospitals, each case can vary significantly.

Consult your vet for more targeted advice. You might also consider seeking a second opinion, especially from specialists in oncology or radiology, to get a more comprehensive understanding of your dog's condition.

All the best to you and your dog and please keep us up to date on your dog's condition.

Jeff
Editor and Publisher
Dog Health Guide

Please note: This information is intended to complement, not replace, the advice of your pet's veterinarian. Always consult a vet for professional medical advice about your pet's health.