Just be aware of this side effects....

A retrospective case series on bisphosphonate related osteonecrosis of the jaw in 20 cats

Suzanna L Hatunen 1, Jamie G Anderson 2, Cynthia M Bell 3, Hugo C Campos 4, Matthew D Finkelman 4, Bonnie H Shope 1

Background
Medication-related osteonecrosis of the jaw (MRONJ) is a severe condition primarily documented in human medicine, associated with long-term use of bisphosphonates and other antiresorptive or antiangiogenic therapies. In veterinary literature, MRONJ has been scarcely reported in cats, with only isolated case reports available. This retrospective study presents a detailed case series of feline MRONJ associated with bisphosphonate treatment, aiming to increase awareness of this condition among veterinarians and provide a basis for future preventive and therapeutic guidelines.

Methods
This retrospective case series analyzed medical records from 20 cats diagnosed with MRONJ between 2015 and 2021. Inclusion criteria followed the 2022 AAOMS MRONJ definition. Data collected included patient signalment, clinical presentation, bisphosphonate treatment details (primarily oral alendronate), diagnostic imaging, histopathology, bacterial cultures, treatment interventions, and outcomes. Imaging (dental radiography, CBCT, conventional CT) was evaluated by a board-certified human oral-maxillofacial radiologist. Histopathologic analyses were reviewed by veterinary pathologists. Descriptive statistics and nonparametric tests were used to explore associations with outcomes.

Results
All 20 cats had received alendronate, primarily for idiopathic hypercalcemia. MRONJ lesions were typically focal (80%), with equal involvement of the mandible and maxilla (each 45%). Lesions commonly followed dental extractions (85%) and were associated with exposed bone or fistulas. Radiographic findings varied but often included irregular radiopaque areas and bone enlargement. Histopathology revealed chronic osteomyelitis in all biopsied cases, often with necrotic bone and bacterial colonization. Treatment involved surgical debridement in 95% of cases; 35% required revision surgeries. Full clinical resolution occurred in 45%, while 10% were euthanized and 35% were lost to follow-up. No statistically significant associations were found between outcomes and variables such as dose, duration of bisphosphonate therapy, or surgical intervention timing.

Limitations
Key limitations include the retrospective design, small sample size, lack of a control group, and heterogeneity in diagnostic and therapeutic approaches. Diagnostic confirmation of idiopathic hypercalcemia was variable across cases, potentially introducing misclassification. The absence of standardized follow-up and data gaps in several records further limited outcome assessment and statistical power.

Conclusions
Alendronate therapy for idiopathic hypercalcemia in cats may predispose to MRONJ, especially following dental extractions. Diagnosis relies heavily on clinical history and examination, as no single diagnostic modality was pathognomonic. Surgical debridement was the most effective treatment strategy, although recurrence was common. Preventative measures, including completing necessary dental procedures prior to bisphosphonate administration and ongoing oral health monitoring, are strongly recommended. Greater awareness and further prospective studies are needed to establish prevalence, risk factors, and optimal treatment protocols for feline MRONJ.

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