Small Animal Orthopaedics Q&A 12

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An eight-year-old, female Brittany Spaniel was evaluated because of swelling and lameness in all four limbs. The distal limb swelling was warm, firm and painful on deep palpation. All four limbs were equally affected. A lateral view radiograph of the dog’s right antebrachium is shown. The left radius and ulna and both tibias had similar abnormalities.

Question	Answer		Article
What is the diagnosis?	Hypertrophic osteopathy or HO. This disease has also been called hypertrophic pulmonary osteopathy and hypertrophic pulmonary osteoarthropathy because of its frequent association with pulmonary disease. HO is a secondary disease found in association with chronic pulmonary diseases such as primary or secondary lung neoplasia, chronic bronchopneumonia or pulmonary abscess, and dirofilariasis. The disease has also been reported in dogs with bladder neoplasia and with hepatic adenocarcinoma.		Link to Article
What other diagnostic tests should be performed to further evaluate this dog?	Radiographs of the thorax should be obtained to search for the primary disease responsible for the HO. If the thorax is normal, radiographic or ultrasound examinations of the abdomen should be obtained. The thoracic radiographs of this dog revealed a primary lung neoplasm in the right caudal lobe and dirofilariasis.		Link to Article
Discuss the purported pathophysiology of HO.	Two theories have been proposed: the humoral theory and the neuronal theory. Neither theory is universally accepted and neither has been fully substantiated. The humoral theory suggests that thoracic diseases cause an opening of arteriovenous shunts in the lung that permit the release of vasoactive substances into the arterial circulation. These vasoactive substances, normally destroyed by the lung, cause increased peripheral blood flow in the limbs resulting in HO. Peripheral vasodilation has been experimentally induced with arteiovenous shunts, but HO has not been produced. The neuronal theory suggests that neural reflexes produced within thoracic tumors stimulate afferent fibers of the vagus nerve that subsequently stimulate efferent fibers of the distal limbs resulting in increased blood flow and the production of HO. The origin of these neural reflexes is open to question, but HO has been induced by stimulation of afferent nerve fibers believed to originate in the pulmonary hilus, mediastinum and parietal pleura. Additionally, HO will resolve when the vagus nerve is severed near the pulmonary hilus. HO also quickly regresses with appropriate treatment of the primary disease.		Link to Article