Lady is a 14 year old dog who presented to the Route 516 Animal Hospital with a 1 month history of intermittent limping. She had been healthy, in general, although her owner was concerned about arthritis in her legs or hips. Upon physical exam, Lady had few abnormalities. She had advanced dental disease and was not bearing weight on her left front leg. An orthopedic exam revealed a large swelling in the shoulder area and she greatly resisted full extension of her front limb. Lady’s owner agreed to various diagnostics including radiographs of her arm and bloodwork. The x-rays revealed that a large mass was growing in her shoulder area and had obliterated much of her humerus (the upper long bone of the arm). The tumor was soon after biopsied and the pathology report revealed it was an osteosarcoma (OSA).
Bone masses are very serious in nature because they are invasive in nature and usually are malignant. Osteosarcoma accounts for 85 % of primary bone tumors and can occur in cats and dogs and even exotic animal such as ferrets . It is most common in large and giant breed dogs especially Great Danes, German Shepherd, Rottweilers, Saint Bernards, Boxers, and Irish Setters. The median age for osteosarcoma is 7 years although it can occur at a much younger age. Symptoms of OSA can be subtle in the beginning. Often pets will exhibit a slight limp or have an area of tissue swelling. Some pets show no symptoms and will acutely fracture their leg in the area where the tumor has eaten away at the bone. OSA occurs primarily in the long bones of the skeletal system but can occur in any bony area . In the front leg it is often found in the shoulder or wrist and in the hind leg near the knee.
Osteosarcoma is best diagnosed with radiographs. On the x-rays the bone will have a mottled look (moth-eaten) where bony lysis (erosion) has occurred. A bone biopsy will verify the type of cancer. Sometimes the biopsy process can be risky because the bone is in a weakened state and could splinter and fracture. After confirmation of OSA, it is important to check radiographs of the lungs. By the time limping is evident, the cancer has often already metastasized to the lungs. Even if the lungs appear normal to the naked eye, there are often microscopic nodules in the lungs already. The median life span for a dog with OSA that has spread to the lungs is 1 ½ months.
The prognosis for osteosarcoma is poor. With no medical intervention, the patients without metastisis, have an average life expectancy of 2-3 months. Because OSA is a very painful disease, owners often opt to humanely euthanize their pets to end any future suffering. Another option includes amputation in order to remove the source of pain. This is not a good option if the pet has other orthopedic problems with the 3 remaining legs such as hip dysplasia or advanced arthritis. However, many pets ambulate well on 3 legs. Even though the cancerous leg is gone, these pets still have an average life span of 3-4 months (due to likely microscopic circulation of cancer). Another option includes pairing amputation with chemotherapy. These pets have a slightly longer survival time of 9 months.
Lady’s owner opted to remove her leg and to administer chemotherapy. Unfortunately, Lady did not tolerate the chemo well and had to discontinue the treatments. She did well on 3 legs and lived for an impressive 17 more months. If you notice your pet has a limb swelling and limping, have your veterinarian take radiographs of its leg. There are many possible causes ranging from a soft tissue sprain to a torn ligament to a fracture to cancer. It is important to rule out osteosarcoma as a possible cause due to the severity of the disease, especially if you own an older, large breed dog. Many causes of limping can be managed with rest and pain medications or with surgical intervention. However, a diagnosis of OSA is a much more serious and holds a grave prognosis.