Forelimb Lameness in a Dog
Sonographer: Anne Desrochers DVM DACVIM
Age: 13 year-old
Breed: Great Dane Mix
Gender: Spayed Female
The patient presented for toe-touching lameness of the left front limb and severe muscle atrophy over the scapula. The patient previously tested positive for Lyme disease and Ehrlichia using a 4DX Snap test and had just finished a 30-day course of doxycycline and 60-day course of Carprofen prior to presentation. CBC, blood chemistry and T4 level were all within normal limits.
Ultrasound evaluation of the left front limb revealed the presence of a mixed echogenicity mass extending from the dorsal aspect to the mid distal portion of the scapula. The mass contained multiple anechoic to hypoechoic fluid-filled cavitated areas. The mass measured at least 2.9x4.2x7.8cm in diameter. A few hyperechoic areas casting mild acoustic shadows were seen within the mass consistent with areas of mineralization. Vascular signal was obtained when assessing the mass with color flow Doppler. The musculature normally located in the area could not be clearly identified. The scapula and scapular spine had a mild irregular hyperechoic bone surface. The subcutaneous soft tissue surrounding the mass was severely hyperechoic and thickened. The presence of mild diffuse subcutaneous anechoic fluid/edema was present within the axillar region.
Ultrasound-guided fine-needle biopsies of the mass and superficial bone were obtained under light sedation.
A diagnosis of osteosarcoma was definitive (100% confidence) upon cytologic evaluation. Nucleated cell population predominated individual round to spindle shaped cells (osteoblasts) with fewer large multinucleated giant cells (osteoclasts) were identified.
Osteosarcoma is the most common primary bone tumor found in dogs. It accounts for up to 85% of all malignancies originating in the skeleton. It mostly occurs in middle aged to older dogs, with a median age of 7 years. Larger breeds have a high propensity due to their size and weight. Dogs over 80 pounds have been shown to be at least sixty times more likely to develop an osteosarcoma than dogs weighing less than 75 pounds. Intact males and females are also highly predisposed. Osteosarcoma can occur in any bone but the limbs account for 75%-85% of all affected bones. The exact causes of osteosarcoma remain known. But factors like ionizing radiation, chemical carcinogens, foreign bodies, and pre-existing skeletal anomalies like site of healed fractures or chronic osteomyelitis sometimes leads to osteosarcoma. Genetic factors are also believed to induce the development of tumors. Dogs with osteosarcoma have been found to have aberrations of the p53 tumor suppressor gene. On radiographs, osteosarcoma usually has a typical "lytic” appearance. If a suspicious area is detected on radiographs, either a fine-needle aspirate or a bone biopsy of the lesion is needed to make a final diagnosis. Up to 90% of these tumors will have metastasized to the lungs at the time of diagnosis. Amputation of the affected limb is the standard local treatment. Various methods of limb-sparing surgery have also described in the literature. Surgery is followed by systemic chemotherapy for the treatment of distant metastatic lesions. Drugs commonly administered include cisplatin, carboplatin, or doxorubicin. Radiation therapy has also been used to control pain in certain cases. Prognosis for patients with osteosarcoma depends on several factors but the average survival rate in dogs treated with surgery and chemotherapy is approximately 1 year.
Additional diagnostic tests to detect the presence of metastatic lesions and consultation with an oncology service to provide additional diagnostic and therapeutic advices were recommended but not pursued. The patient was kept on Carprofen, Tramadol and Gabapentin daily for the following 2 months at which point the mass had doubled in size and the owner opted for humane euthanasia.
Special thanks to Dr. Leah Knode and the staff at House Paws Round Hill and Casey J. LeBlanc DVM, PhD, Diplomate ACVP (Eastern VetPath) for their help with this case.