Hypertrophic Osteopathy (HO)

HO is a severely debilitating disease which occurs secondary to other diseases. The primary disease is usually a cancer, but occasionally infectious diseases such as tuberculosis can be the primary disease.  Most often they involve the lungs or are disease processes lying within the chest.  Affected dogs develop bilateral, symmetrical soft tissue swelling of the lower legs with periosteal new bone formation. These bony changes do not involve the joints or joint capsule.

The precise cause of HO is not yet understood, but the blood flow to the lower limb is greatly increased in the early stages of the disease. Secondary lung cancer is the disease most often associated with HO, and primary lung cancer and primary bone cancer with secondary spread to the lungs are also very commonly reported. Dogs that have had amputation for bone cancer have a predisposition to develop HO. Dogs infected with spirocercosis and heartworm may develop HO.

Any breed of dog can be affected, but large and giant breed dogs are most often taken to veterinarians with the disease. Except for large and giant breeds of dog which can develop bone cancer at an early age, the age of onset is usually middle-aged to older animals, reflecting the increasing incidence of cancers with advancing age. Females are more often affected than males, possibly related to the common occurrence of mammary carcinomas.

Usually dogs are taken to the veterinarian because they are lame and reluctant to move around. They have symmetrical firm soft tissue swellings of the lower legs. The limbs are warm to touch and often very painful when pressed.

The diagnosis is confirmed by X-rays. In the early stages soft tissue swelling is seen, but this is followed by new bone development which can appear to be smooth, or irregular. Most often the metacarpal or metatarsal bones are affected. Radiographs of the chest will frequently identify the underlying disease process. If the primary disease process can be successfully treated the bony changes regress.

In dogs, HO needs to be differentiated from osteomyelitis, bone tumors, hypertrophic osteodystrophy in young dogs, panosteitis, osteoarthritis (in the early stages) and the soft tissue swelling from edema.

Successful treatment depends upon the underlying cause. Secondary lung cancer brings with it a very poor prognosis and euthanasia usually results. However, some causes such as heartworm infestation and primary lung tumors can be treated by surgical removal of the underlying cause, with good results,
otherwise treatment is the use of analgesics to relieve pain.

Sometimes dealing with HO as with cancer it helps to know you are not alone.  Please visit Kelsey's story and please keep Kelsey in your prayers.

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