Hypertrophic Pulmonary Osteopathy

Dear Dr. Jody:  Our 7 year old German shepherd, Harley, has suddenly become quite painful in all four legs.  His paws seem swollen, and he is having a very hard time walking.  He doesn’t even want to get up to eat his meals because it hurts too much for him to move.  We tried giving him aspirin but it didn’t seem to help.  What could be going on with Harley?

Although there are numerous possibilities that could explain painful limbs in an older German shepherd, my main concern for Harley is a condition known as Hypertrophic Pulmonary Osteopathy (HPO).
 

HPO is a poorly understood but well documented disease of middle-aged and older large breed dogs, most notably German shepherds and Rottweilers.  Interestingly, the condition does not start in the limbs.  Most affected patients have some sort of significant lung disease (hence the word “pulmonary” in the name of the illness) which in turn may have originated elsewhere in the body.  The usual presentation is a dog with underlying lung cancer (either a primary lung cancer or cancer that has spread to the lung from another part of the body) or other severe lung disease such as a widespread fungal infection.

 

But why would lung disease result in a painful swelling of the feet?  It has been suggested that affected dogs have an unusual nerve message being transmitted from the chest to the extremities.  This unhelpful nerve impulse causes increased blood flow to the paws and results in excessive growth of new connective tissue and bone in these areas.  This sudden increase in blood flow and unnecessary growth of tissues results in excruciatingly painful swelling of all four limbs.  Affected patients may have a history of recent unexplained weight loss, coughing, or wheezing due to the underlying lung disease.

Your veterinarian will need to x-ray Harley’s limbs as well as his chest to arrive at a diagnosis.  Sedation may be required for this procedure, as the necessary manipulation of the painful limbs would be unbearable in a conscious patient.  The characteristic radiographic lesions that your veterinarian is searching for are periosteal inflammation and evidence of pulmonary disease.  Periosteal inflammation is a fuzzy-looking growth along the edges of the bones in the paws.  Patches of consolidation on the lung x-ray would point towards cancer or fungal infection.

In cases where the primary lung condition is treatable (such as a fungal infection), the painful swelling in the limbs can resolve after successful treatment of the lung disease.  Sadly, most patients with HPO do in fact have lung cancer.  Without aggressive and costly treatment of the cancer at a referral centre, the only humane treatment for HPO is euthanasia.  Early recognition of the condition is the key to avoiding unnecessary distress in your four-legged friend.