Kansas City Veterinary Medical Association

Case Study: Hypertrophic Osteopathy

by Andrea Grow, DVM

Image 1: Lateral abdomen – note the periosteal changes on the femurs and pelvis. Image 2: Ventrodorsal pelvis – note the periosteal changes on the femurs and pelvis. Image 3 & 4: Lateral thorax (right and left) – note multiple pulmonary masses; note periosteal changes on distal humerus.

“Whisper”, a 10-year-old spayed female beagle, was referred to our clinic (Veterinary Center of Liberty) for evaluation of weakness and discomfort in the rear legs and back. The owners had noticed a slow progression of weakness, discomfort, decreased mobility and difficulty/reluctance to walk for approximately one month. Physical examination revealed decreased musculature of the rear legs along with a generalized loss of lean body mass. A painful response was elicited on flexion/extension of coxofemoral joints bilaterally. Spinal and pelvic radiographs revealed periosteal irregularities along the diaphysis of both femurs and the surfaces of the pelvis. Symmetrical bony proliferation along the cortices had a scalloped and lacy appearance. Thoracic radiographs revealed numerous pulmonary masses. Abdominal radiographs appeared normal for age and breed.

The bony abnormalities described were suggestive of hypertrophic osteopathy (also known as secondary hypertrophic osteopathy, hypertrophic pulmonary osteopathy). Hypertrophic osteopathy (HO) is considered a paraneoplastic syndrome that develops in conjunction with intrathoracic or intraabdominal disease, most often neoplasia. Of 180 canine cases, 98% had intrathoracic disease, and 92% of these had either metastatic lung neoplasia or primary tumors of the lung (Ettinger). Tumors associated with hypertrophic osteopathy include pulmonary adenocarcinoma, bronchoalveolar carcinoma, squamous cell carcinoma, esophageal sarcoma, nephroblastoma and urinary bladder neoplasms. Less common underlying etiologies include pneumonitis/pneumonia, abscesses, fungal granulomas, endocarditis and heartworm disease.

Clinical signs associated with limb changes often precede signs of thoracic disease. The patient usually develops firm, warm or painful, nonedematous swelling in all four limbs. Affected animals are often stiff and reluctant to move, which may be mistaken for osteoarthritis.

Diagnosis of hypertrophic osteopathy is made by demonstrating a primary lesion in the thorax or abdomen along with characteristic changes of the appendicular skeleton. Skeletal pathology includes changes in bilateral symmetry, periosteal proliferation and scalloped or lacey irregularities of the bone cortices. These lesions are not to be confused with the bony metastasis of a primary tumor.

The exact pathophysiology of hypertrophic osteopathy is unknown. Research suggests a neural reflex originating in the thorax that causes increased blood flow to the distal extremities, which in turn causes the overgrowth of connective tissue at the level of the periosteum. Regression of the osteopathy may follow the removal of the source of this neurological and vascular stimulation.

Treatment of hypertrophic osteopathy is to identify and treat the underlying pathology if possible. Resection of the primary lesion or tumor, lung lobectomy, intercostals nerve resection, subperiosteal rib resection and vagotomy have been described in veterinary literature. Supportive therapies for hypertrophic osteopathy include prednisone or other non-steroidal anti-inflammatory agents to palliate the clinical signs and reduce inflammation. Chemotherapy with cisplatin has been mentioned in the literature, but its efficacy has not been proven (ACVIM 2008).

The above information and options for supportive care were discussed with the owners. Considering the poor prognosis and age of the dog, the owners elected humane euthanasia.

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