Idiopathic bilateral osteonecrosis of the maxilla in a standard poodle. Though not a case of MRONJ, this appearance can be typical for both idiopathic osteonecrosis and MRONJ. Photo courtesy Dr. John R. Lewis I am writing this from 31,000 feet as I return from the annual Veterinary Dental Forum (VDF) in Palm Springs, Calif. Always a great event, the VDF has many different lecture tracks, including beginner, intermediate, advanced, and original research tracks. Two lectures discussed an emerging problem I would like to bring awareness to for our Veterinary Practice News readership. Bisphosphonates are a group of osteoclast-inhibiting drugs that slow the progression of osteoporosis in humans. Drugs in this category, such as alendronate and pamidronate, are used in veterinary patients to treat idiopathic hypercalcemia and osteosarcoma. There is a well-documented side effect of these drugs that can be a life-threatening sequela to their use. Human and veterinary patients who receive these medications can develop osteonecrosis of the mandible or maxilla, where large portions of the jaw may become devitalized, resulting in erosion of the soft tissue overlying the bone. Inappetence, anorexia, and secondary bacterial infections ensue, resulting in a poor quality of life. A review of bone biology Bone is constantly remodeled based on the forces placed upon it (Wolff’s Law). Osteoblasts of mesenchymal origin are responsible for laydown of new osteoid, and osteoclasts of hematopoietic (monocyte/macrophage) origin are responsible for removal of bone. Osteonecrosis is normal at a cellular level, but not at a macroscopic level. When bone dies, osteoclasts remove dead bone. Medications that inhibit osteoclast activity may work too well; they not only decrease osteoporosis, but sometimes can also result in accumulation of necrotic bone that cannot be scavenged.1 BRONJ, or bisphosphonate-related osteonecrosis of the jaw,2 is defined as an area of exposed bone in the maxillofacial region that does not heal within eight weeks after identification by a health care provider, in a patient that was receiving or had been exposed to a bisphosphonate and had not had radiation therapy of the craniofacial region.3 Since bisphosphonates are not the only type of drug that can cause osteonecrosis, BRONJ is now considered a subset of MRONJ, which stands for medication-related osteonecrosis of the jaw. Other drugs may cause similar side effects, such as RANKL inhibitor denosumab, steroids, immunomodulators, and chemotherapy drugs.4 Prevalence and treatment Cats are more commonly affected by MRONJ than dogs, likely due to the prevalence of idiopathic hypercalcemia in the feline species. A recent retrospective study5 assessed 20 feline cases of MRONJ. All 20 patients were currently receiving alendronate, and one patient previously received pamidronate. Patients had been receiving bisphosphonates between five and 66 months prior to diagnosis. Dosage at the time of diagnosis ranged from 7.5 to 60 mg once per week. The majority of patients had bisphosphonates discontinued before or at the time of surgical treatment of osteonecrosis. Sixteen (80 percent) had a focal lesion in only one dental quadrant. Two patients had lesions in both the maxilla and mandible. Seventeen patients (85 percent) had prior dental extractions at the same location as the lesion.5 Treatment of MRONJ varies, including conservative therapy (doxycycline, pentoxifylline, niacinamide),4 aggressive debridement, extractions, sequestrum removal, and mandibulectomy/maxillectomy. In a retrospective study of 20 feline patients, 35 percent of patients needed at least one revision surgery.5 One patient required nine surgeries, and one patient was euthanized at the time of initial diagnosis.5 Cats are not as quick to recover from mandibulectomies as dogs are, and 12 percent of cats will not regain the ability to eat on their own after mandibulectomy.6 Since treatment is not always effective, prevention is key. Thorough dental screenings prior to bisphosphonate use, extraction of severely diseased teeth prior to use of bisphosphonates, meticulous oral hygiene, and avoiding the use of concurrent corticosteroids (due to their catabolic effects on bone) have been suggested.1 Tooth extraction in patients receiving bisphosphonates can trigger osteonecrosis, so root canal therapy may be an alternative depending on the dental problem. Taking a “drug holiday” from bisphosphonates prior to dental extractions is of questionable value due to their long half-life in bone. However, temporary and possibly permanent discontinuation may be recommended. John R. Lewis, VMD, DAVDC, FF-OMFS, practices and teaches at Veterinary Dentistry Specialists and Silo Academy Education Center in Chadds Ford, Pa. References Stepaniuk K. Bisphosphonate related osteonecrosis of the jaws: a review. J Vet Dent. 2011; 28(4): 277-81. Ruggiero SL. Bisphosphonate-related osteonecrosis of the jaw (BRONJ): initial discovery and subsequent development. J Oral Maxillofac Surg 2009; 67 (5 Suppl):13-18. Ruggiero SL, Dodson TB, Assael LA, et al. American Association of Oral and Maxillofacial Surgeons position paper on bisphosphonate-related osteonecrosis of the jaws--2009 update. J Oral Maxillofac Surg 2009; 67(5 Suppl): 2-12. Hoffman, S. Atypical presentation and conservative treatment of idiopathic osteomyelitis and osteonecrosis in a dog. Proceedings of the 38th Annual Veterinary Dental Forum (2024): pp.21-24. Hatunen SL, Anderson JG, Bell CM, Campos HC, Finkelman MD, Shope BH. A retrospective case series on bisphosphonate related osteonecrosis of the jaw in 20 cats. Front Vet Sci. 2024;11:1436988. Northrup NC, Selting KA, Rassnick KM, Kristal O, O'Brien MG, Dank G, Dhaliwal RS, Jagannatha S, Cornell KK, Gieger TL. Outcomes of cats with oral tumors treated with mandibulectomy: 42 cases. J Am Anim Hosp Assoc. 2006;42(5):350-60.
