Women aren't the only ones suffering from decreased bone density and bone mass loss--horses in Central California have experienced a systemic osteoporotic disorder. At the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif., Amanda Murray, DVM, MPVM, of the University of California, Davis, presented a paper on equine bone fragility syndrome, a systemic osteoporotic (characterized by a decrease in bone mass) syndrome identified in specific areas of California and thought to be caused by exposure to cristobalite. This mineral is found in chalk rock in the Carmel/Monterey Bay region and is thought to occur in volcanic formations in Sonoma and Lake Counties of California. Exposed cristobalite-rich soils are readily aerosolized when the ground is disturbed by excavation.

This syndrome is thought to be associated with pulmonary silicosis (a silicate dust-caused respiratory disease that in humans might be accompanied by rheumatoid arthritis). With disease progression an affected horse suffers from skeletal deformities and, ultimately, pathologic fractures.

In a previous study 19% of horses affected by bone fragility syndrome had concurrent pulmonary silicosis, and 58% of horses with chest radiographs had signs of lung disease. In many cases the pulmonary disease can be silent (no obvious clinical lung signs). This disease is not restricted to any particular age, breed, or gender.

Skeletal deformities most often begin with bowing of the scapula (shoulder blade). While bone disease can manifest years after exposure to the mineral, scapular bowing might be noted suddenly, beginning on one side and progressing to both shoulders. Excessive bone production leads to thickening of the scapular spine and irregular contours of the scapula due to ongoing bone destruction and resorption.

Another skeletal deformity that occurs is lordosis (extreme swaying of the back). Dropping of the tuber coxae (points of the hip) of the pelvis can also be present. The disease might affect the cervical vertebrae (in the neck), causing reduced range of motion, pain on palpation, and, in some cases, reluctance to extend the neck to eat off the ground. Only occasionally are there skeletal changes in the lower limbs.

Respiratory disease might be characterized by flaring of the nostrils at rest. Pulmonary fibrosis (the formation of excess fibrous connective tissue as a result of a reparative or reactive process) related to persistent inflammation caused by cristobalite crystals might be visualized on radiographs. Once a horse is exposed, these crystals are not broken down, released, or eliminated from the lungs.

Lameness is variable, as are gait abnormalities and stiffness. Early signs might include vague lameness or stiffness. Nuclear scintigraphy that reveals the hallmark of multiple "hot spots" in multiple bones is the best means of early diagnosis, along with lung radiographs. Fluid washes of the lungs and trachea can used to diagnose pulmonary disease.

Research at UC Davis is under way to identify serum markers that can be used for early detection. Current treatments involve minimizing inflammation and distress. In advanced cases, the most humane option is euthanasia. Prevention is key--avoid excavation in endemic areas of this mineral deposit, mulch or cover exposed soil, and use sprinklers to decrease dust.

Read more.

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from TheHorse.com. Learn More