Hypertrophic Osteopathy in Small Animals
Hypertrophic osteopathy (HO) can occur with multiple tumor types; it is most commonly associated with primary lung tumors. HO can also occur with metastatic lung tumors (particularly from osteosarcoma), urogenital tumors (renal carcinomas, botryoid rhabdomyosarcoma of the bladder, and nephroblastoma), malignant schwannomas, and other carcinomas (eg, esophageal, pancreatic).
HO is exceptionally rare in cats.
The pathophysiology of HO is not well understood.
HO is characterized by an exuberant periosteal reaction that is evident on radiographs (see hypertrophic osteopathy image). It is considered a painful condition and is often associated with soft tissue swelling along the limbs, in addition to lameness (sometimes shifting).
Courtesy of Dr. Brooke Britton.
Evidence of HO on radiographs is distinctive; when it is recognized, thoracic radiography is indicated.
Treatment of HO centers on pain management and treatment of the underlying cancer. NSAIDS/opioids, gabapentin, amantadine, and sometimes bisphosphonate therapy are typically used to treat HO-associated pain.
Fever in Small Animals
Fever is a nonspecific clinical sign that occurs in many veterinary cancer patients during the course of their disease.
Paraneoplastic fever typically results from activation of the innate immune response against tumor antigens, or in response to tumor necrosis. It is mediated primarily by inflammatory cytokines that activate cellular cascades that ultimately affect the thermoregulatory center within the hypothalamus (1).
Concurrent infection of a tumor, perforation of GI masses that causes septic peritonitis, and leukopenia due to myelophthisis (secondary to involvement of hematologic cancer within the bone marrow) can also cause fever. Fever generated by these causes must be differentiated from fever that develops as a complication of cancer treatment (ie, febrile neutropenia secondary to chemotherapy treatment, or as a result of urinary or respiratory tract infections secondary to myelosuppression from cancer treatment).
Paraneoplastic fever is typically treated with specific antitumor therapy, such as chemotherapy, to address the underlying cancer. In the author’s experience, paraneoplastic fevers in the absence of infection rarely exceed 39.7°C (103.5°F). Typically, these fevers wax and wane, such that specific medications aimed at decreasing fever (eg, NSAIDs) are not also required.
Key Points
Hypertrophic osteopathy is most commonly associated with primary lung tumors and is characterized by an exuberant periosteal reaction evident on radiographs.
Paraneoplastic fever typically results from activation of the innate immune response against tumor antigens, or in response to tumor necrosis.
For More Information
Bailey DB. Paraneoplastic syndromes. In: Vail DM, Thamm DH, Lipták JM, eds. Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed. Elsevier; 2020:98-100.
Withers SS, Johnson EG, Culp WTN, Rodriguez CO, Skorupski KA, Rebhun RB. Paraneoplastic hypertrophic osteopathy in 30 dogs. Vet Comp Oncol. 2015;13(3):157-165. doi:10.1111/vco.12026
Also see pet owner content regarding peripheral nerve disorders in dogs and cats.
References
Ramsey JK, Tasker S. Fever. In Ettinger SJ, Feldman EC, Cote, eds. Textbook of Veterinary Internal Medicine. 8th ed. Elsevier; 2017:195-203.
