What is Bone Fragility Syndrome?
Horses that live or have lived in certain coastal counties in northern California can develop a degenerative disorder known as bone fragility syndrome. Affected animals develop progressive bone loss that starts out as vague signs of lameness and stiffness, but leads to skeletal deformities like bowing of the scapula, severe swayback, and dropping of the pelvis. Although there is still a great deal to learn about this disease, but new treatments are being researched to slow or stop the progression of the disease.
Bone fragility syndrome is a disorder that is restricted to horses who live or have lived in areas of northern California where toxic crystalline silica called cristobalite is found.
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Symptoms of Bone Fragility Syndrome in Horses
This disease is restricted to horses that live or have spent considerable time in some parts of California. Signs that a horse has developed this disorder can include:
- Bowing of the shoulder blades
- Dropping of the hip
- Incomplete bone fractures
- Reduced range of motion
- Reluctance to exercise
- Weight loss
Horses with bone fragility syndrome have lived in the regions of northern California where the soil containings a toxic crystalline silica known as cristobalite. Cristobalite is just one of several crystalline and cryptocrystalline polymorphs of silica. The crystalline polymorphs of silica include:
The cryptocrystalline silicas are made up of crystalline shapes so small that they are nearly undetectable. These types of silica include:
Causes of Bone Fragility Syndrome in Horses
This is a relatively recent disorder that is localized to just a few counties in northern California. Scientists are still trying to understand the underlying cause, but signs point toward exposure to a high-temperature polymorph of silica known as cristobalite. Cristobalite is found in the soil of the areas that the disease is found in which is prone to becoming aerosolized and inhaled. It is not understood why horses that are exposed to cristobalite in other geographical areas do not develop this disease.
Diagnosis of Bone Fragility Syndrome in Horses
If the disease has not progressed very far, the horse may present with only a few vague symptoms of stiffness and mild lameness. In these cases, the diagnosis will generally start with a complete physical, with particular attention being paid to the legs and feet. A full history of the animal is usually requested at any diagnostic appointment, including its activity levels, diet, and living conditions, and the examining veterinarian will also probably conduct a lameness exam to evaluate the animal moving at different gaits.
Radiography is usually the first imaging technique that is used in equine medicine and will help to diagnose if any microfractures have occurred, and ultrasound technology may uncover the amount of bowing of the scapulas. The final diagnosis is generally made by a bone scintigraphy. In a bone scintigraphy, the patient is injected with a short-acting radioisotope, sedated, and then visualized using a specialized gamma camera.
Treatment of Bone Fragility Syndrome in Horses
There is no treatment that will reverse the course of this disorder, however, there are several treatments that can be used to ease the symptoms. NSAID pain medications are used to reduce pain and inflammation, and corticosteroids have also been utilized for horses with bone fragility syndrome, particularly when the spine has been compromised. Tiludronate is a biphosphate medication that is designed to prevent the breakdown of the bone and increase bone density, but initial attempts to medicate horses with tiludronate have been less than promising.
The medication zoledronate, or zoledronic acid, is designed to slow down bone reabsorption and is utilized as a treatment for humans with the degenerative disorder of the bone known as Paget’s disease. Preliminary trials to treat bone fragility syndrome with zoledronate have shown some improvement in the amount of lameness and musculoskeletal pain, although further research is required before it is more widely used. This disorder is eventually fatal.
Recovery of Bone Fragility Syndrome in Horses
A high percentage of horses who develop bone fragility syndrome frequently develop concurrent cases of pulmonary silicosis. Pulmonary silicosis is a disease of the respiratory system that can strike when specific types of silicate dust are inhaled. These tiny crystalline structures lodge in the lungs causing scarring of the lung tissues, and immune responses are often launched by the body as well, causing further inflammation. In extreme cases, silicosis can cause auto-immune disorders as well.
The prognosis for this disease is poor, and although there are some therapies that may temporarily improve the patient’s situation, Bone fragility syndrome is eventually fatal.