Panosteitis

Panosteitis, sometimes shortened to pano among breeders, is an occasionally seen long bone condition in large breed dogs. It manifests with sudden, unexplained pain and lameness that may shift from leg to leg, usually between 5 and 14 months of age, earning the nickname "growing pains. " Signs such as fever, weight loss, anorexia, and lethargy can also be seen. The cause is unknown, but genetics, stress, infection, metabolism, or an autoimmune component may be factors. It has also been suggested that rapid growth and high-protein food are involved in the pathogenesis. Whole blood analysis may show an elevated white blood cell count; this finding lends support to the theory that panosteitis is due to an infection.

Panosteitis is characterized histologically by an increase in activity of osteoblasts and fibroblasts in the periosteum, endosteum and bone marrow, resulting in fibrosis and the formation of connective tissue in the medullary cavity of the affected bone. Pain may be caused by increased pressure in the medullary cavity and the stimulation of pain receptors in the periosteum.

The humerus is most commonly affected. Males are more commonly affected than females.