An 11-year-old female spayed Australian shepherd presented to DoveLewis Emergency Animal Hospital with a several month history of left thoracic limb swelling and lameness. No response to antibiotic/anti-inflammatory medications were reported. Severe soft tissue swelling extending distally from the elbow to the digits was noted on physical exam. A single radiograph of the left thoracic limb was made and is included for interpretation (Figure 1).
Figure 1: Radiograph of left thoracic limb.
The single view provided demonstrates severe soft tissue swelling. No evidence of a radiopaque soft tissue foreign body was identified. There is smoothly marginated, palisading periosteal reaction involving the abaxial aspects of the fifth metacarpal bone and proximal phalanx of the 5th digit as well as some smoothly marginated periosteal reaction involving the abaxial aspect of the first digit. There is some irregularity involving the medial aspect of the distal radius and mild concurrent degenerative carpal changes are noted. These radiographic findings raised suspicion for hypertrophic osteopathy and thoracic radiographs were made and are available for evaluation (Figure 2a, b).
Figure 2a: Lateral thoracic radiograph.
Figure 2b: Ventrodorsal thoracic radiograph.
There is a very large mass involving the dorsal aspect of the right caudal lung lobe with a large pulmonary nodule on the adjacent left side. A smaller soft tissue pulmonary nodule is also identified caudal to these lesions on the lateral view only. Primary pulmonary neoplasm with metastatic nodules was the primary differential given this appearance, although this was not proven histopathologically.
Hypertrophic osteopathy is a well-described paraneoplastic disease in the canine patient. The great majority of these patients are ultimately found to have primary or metastatic pulmonary neoplasia; however there have been reported cases of abdominal neoplasia involving the urinary tract or uterus. Non-neoplastic inflammatory/infectious pulmonary disease has been found to be a much less common cause of hypertrophic osteopathy. The osseous changes include non-neoplastic periosteal proliferation involving the phalanges and metacarpal/metatarsal bones of one or more limbs as well as soft tissue swelling. Pathophysiologic changes due to this disease process include increased peripheral blood flow, proliferation of vascular connective tissue and ultimately bone spicule formation.