By Mandy Arens, DVM, MPVM, Ph.D.
Bone fragility syndrome (BFS, also known as bone fragility disorder) is a debilitating bone disease that causes horses to develop lameness, outward bowing of the shoulder blades (scapulae), swayback not associated with advanced age, and neck stiffness. Severe bone loss (osteoporosis) causes these sign along with weakening and, ultimately, spontaneous breaking of bones. The bones usually impacted include the scapulae, ribs, pelvis, and vertebrae. Affected horses progressively worsen until they die from catastrophic bone fracture or are humanely euthanized. The condition can affect horses of all ages, breeds, and genders.
Cause
The cause of BFS remains unknown. However, many affected horses also have a chronic lung disease called pulmonary silicosis that results from inhaling toxic silica crystals from the soil. Once inhaled, these crystals move into the lung tissue and surrounding lymph nodes and incite chronic inflammation. Horses with pulmonary silicosis often exhibit exercise intolerance and, with advanced disease, develop breathing difficulty while at rest. This condition has no cure.
Researchers do not yet understand the connection between BFS and pulmonary silicosis. Not all BFS horses have evidence of pulmonary silicosis, and not all horses with pulmonary silicosis have developed BFS. However, all horses with BFS have lived in certain geographic regions where soils containing these toxic silica crystals (e.g., cristobalite and tridymite) are found. All horses with BFS either lived in California at the time of diagnosis or have a history of living in that state. Within California, affected horses have been diagnosed in many counties along the coastal mountain range and the Sierra Mountains.
Diagnosis
Diagnosis of BFS, particularly in the early stages of disease, can be difficult as the presenting complaints are usually intermittent lameness and body stiffness. The most definitive test for all stages of BFS is nuclear scintigraphy (bone scan); areas of high bone activity associated with bone loss can be seen as bright spots on the bone scan images. In horses with moderate to severe disease, veterinarians can make a diagnosis based on the scapular spine’s widened appearance on ultrasound. And in severe disease bowing of the scapula is evident upon physical examination.
Since the bony changes associated with BFS could occur with any disease that causes systemic bone loss, such as a calcium/ phosphorus imbalance leading to hyperparathyroidism, veterinarians must consider diagnostic test and examination findings in combination with a complete history of physical complaints as well as a history of where the horse has lived.
Treatment and Prevention
Treatment options include pain management with non-steroidal anti- inflammatory medications (NSAIDs such as phenylbutazone or flunixin meglumine) or steroids (e.g., dexamethasone), and administering bisphosphonates (e.g., Tildren and zoledronate) targeting the bone cells causing osteoporosis to prevent bone resorption. Managing pain using NSAIDs and steroids usually becomes ineffective as the disease progresses. Experimental use of zoledronate caused improvement in horses six months after beginning treatment, while the effects of Tildren are anecdotally beneficial for a few months. Thus, both bisphosphonates appear to provide pain relief seen as improvement in lameness and body stiffness; however, the long term effects of these medications on horses with BFS are unknown.
Because of the association between BFS and pulmonary silicosis, most veterinarians recommend dust control and avoiding toxic crystal inhalation as preventive measures. However, these tactics might only solve part of the problem.
Ongoing Research
Research into BFS continues at the University of California, Davis, where investigators are further examining what happens to affected horses’ bones. These studies’ results might provide more insight into treatment options. Additionally, researchers continue to assess zoledronate’s usefulness for treating BFS.
About the Author: Mandy Arens, DVM, MPVM, PhD, recently completed her PhD at the University of California, Davis, where she conducted research on equine bone fragility syndrome.
Article provided courtesy of AAEP Media Partner, The Horse.