Lame German Shepherd DogA 6 year old male German Shepherd Dog presented with a history of progressive forelimb lameness - he had been radiographed at an earlier age and a diagnosis had been made of secondary arthrosis due to bilateral elbow dysplasia as well as secondary arthrosis due to bilateral hip dysplasia.On physical examination there was, as expected, pain on movement of the elbow joints as well as pain on movement of the hip joints.Lateral radiographic views were made of both elbow joints expecting to evaluate the progression of the secondary changes due to the elbow dysplasia.Lateral radiographs of both elbows - What is your diagnosis? Radiographic diagnosisProductive lesions are present in the distal portion of both humeri - the lesions appear to originate from the medullary cavities with expansion creating a periosteal response that is more prominent on the left - cortical destruction is difficult to evaluate with productive lesions such as these but was not thought to be a prominent feature in these lesions - the periosteal new bone is characterized by having being linear with an intact border. The secondary changes diagnostic of elbow dysplasia are more prominent on the left and consist of enthesophyte formation, periarticular osteophytosis, and modeling of the medial coronoid processes - the changes on the right are limited to new bone on the anconeal process and spurring on the distal humeral joint cranially - joint instability is not a prominent feature at this time.A differential diagnosis for the productive polyostotic distal metaphyseal humeral lesions includes those that do not include markedly aggressive changes. these include hematogenous osteomyelitis, fungal bone infection, and metastatic tumors to bone. the radiographic changes in the elbow joints are classic for chronic elbow dysplasia with changes more prominent on the left.Because of the assumption that the clinical signs were the result of elbow and hip dysplasia, studies were made of the pelvic region as well.Ventrodorsal view of the pelvis with a single lateral view of the right femur - What is your diagnosis? Radiographic diagnosisA highly productive lesion originates from the proximal femur - cortical destruction is difficult to ascertain because of the heavy cuff of new bone - the periosteal new bone has a mottled density with an indistinct border with a suggestion of a sunburst pattern - the lesion has an indistinct border with a long zone of transition.The radiographic evaluation is complicated by the changes affecting the right hip joint that include subluxation of the femoral head, shallow appearance of the acetabulum, modeling of the femoral head and neck - these changes are all secondary to the hip dysplasia - the joint instability may also be influenced by disuse of the right pelvic limb - the secondary changes to the hip dysplasia on the left are more subtle with the more prominent change being the thickening of the femoral head and neck. The changes in the forelimbs need to be compared with those in the femur - the major difference is the aggressive appearance in the femur of the periosteal new bone and the long zone of transition of the lesion - a differential diagnosis considering the lesions in three bones still includes hematogenous osteomyelitis, fungal bone infection, and metastatic bone tumor - however, the difference in appearance of the femoral lesion suggest that it is a primary bone tumor with the possibility of metastatic bone lesions in the forelimbs.Because of the possibility of metastatic bone lesions, a skeletal survey was made.A productive lesion with underlying destruction was noted on one of the spinous processes of a thoracic segment (arrows).Age dependent spondylosis deformans was noted adjacent to the disc spaces on several mid-thoracic vertebral bodies. Because of the multiple bone lesions and the possibility of generalized disease, thoracic radiographs were made - Do they assist in your diagnosis? Thoracic radiographic studyMultiple smooth bordered pulmonary mass lesions are present in all lung lobes but more prominent on the right - no evidence of hilar lymphadenopathy is present - atelectasis of the right middle lobe suggests a more prominent collection of lesions in that lobe with possible obstructive atelectasis.Radiographic diagnosis - multiple pulmonary masses are usually due to metastatic tumor spread to the lungs - the absence of any hilar lymphadenopathy tends to make fungal infection less likely.Final radiographic diagnosisThe case is interesting due to the mistaken assumption that the presenting progressive lameness was the result of previously diagnosed elbow and hip dysplasia - the presence of the secondary changes associated with the elbow and hip dysplasia complicates radiographic evaluation - detection of the humeral lesions was strongly suggestive of metastatic tumor because of the patient’s age as well as the medullary origin of the lesions with the less prominent periosteal response - the femoral lesion had an aggressive appearance based on the border and nature of the reactive bone and the long zone of transition - cortical destruction was thought present, but not easily confirmed - the additional lesion in the thoracic spine did little to assist in determining the etiology - the multiple pulmonary lesions strongly suggested metastatic spread of a primary tumor.It is possible that all of the bony and pulmonary lesions are metastatic from an undetected soft tissue primary tumor - The different appearance of the femoral lesion strongly suggests that it is a primary bone tumor with the other lesions metastatic to this tumor - the appearance of the femoral lesion tends to rule out an inflammatory lesion.The diagnosis on necropsy was that of a primary osteosarcoma in the femur with the other lesions having a similar appearance and were assumed to be metastatic.
