The swelling of normally non edematous tissue which lines the outer surface of the long bones, which enables the musculature attachment to the bones, is generally an outward sign of an internal malady that is most likely neoplastic or infectious in nature.  It has also been referred to as hypertrophic pulmonary osteoarthropathy because the underlying disease has most often been found to be pulmonary in nature.  Hypertrophic osteopathy has not only been found in humans and dogs but also in horses, cows, sheep, cats, fowl and other species of animals.

Hypertrophic osteopathy in dogs is defined as an abnormal growth of soft the tissue (periosteum) which lines the outside of the long bones in dogs, generally being secondary  to neoplastic or infectious masses of the abdominal or thoracic cavity.

This condition, normally found in large or giant breeds of dogs, is generally noted at the middle age of the animal, though the underlying cause usually begins at an earlier age.  Here are some of the symptoms you might notice in your canine:

These symptoms not only suggest the abnormal growth and swelling of the soft tissue surrounding the bone (periosteum) but also signal that there are underlying issues at the root of the problem.

Types  

The types of hypertrophic osteopathy are related to the underlying cause of the condition, which most often is pulmonary and neoplastic in nature.  

As noted above, hypertrophic osteopathy can occur as a result of a number of underlying conditions which can afflict various parts of the canine host.  While the pathogenic processes continue to elude research and investigation, the veterinary community has predominantly found:

Large breeds, with Boxers being high on the list, females, and animals average age of 8.5 years or older (considered middle aged) seem to be the most often afflicted with hypertrophic osteopathy and its complications.

Diagnosis of this condition will require your complete history of the patient, which should include diet, known hereditary conditions, activity level, symptoms noted and the duration of those symptoms.  Your veterinary professional will do a physical examination in which he will be watchful of thickening of limbs, non-edematous and firm swelling in the limbs.  This swelling will be distal in location (further away from joint) and will be located in all four limbs and likely with pain elicited with palpation and movement.  He will be noting if the limbs are warm to the touch and if the skin over the metatarsal and metacarpal areas is loose or tight. 

He will likely order blood work and perhaps tissue samples but, ultimately, the diagnosis will be confirmed by radiographic imaging (x-ray). Hypertrophic osteopathy will be displayed on the radiographic imaging as bilateral and symmetrical primarily along the long bones of the skeletal frame.  In the early stages, it is likely that only soft tissue swelling will be noted as the development of the abnormal bony elements of the condition occurs over time.

Sometimes, the skeletal changes will appear months before the onset of any other systemic signs and symptoms of the underlying disease. This makes it ever so important that soft tissue changes be noted and evaluated as early as possible in an attempt to catch the underlying condition as early as possible for treatment.

Once the results of the lab testing (if ordered), radiographic imaging and physical examination are combined with your complete history, your veterinary professional will be able to develop and initiate a treatment plan.  This treatment plan may include any of the following options:

In the case of the underlying cause being found to be primary lung cancer, generally the mass can be removed successfully if caught early enough, thereby giving a better prognosis for the patient.  However, if the cause is determined to be secondary lung cancer, the prognosis is much poorer with euthanasia being the end result.  Keeping up with regular physical examinations and evaluations with your veterinary professional will help identify some of the early symptoms and clinical signs of hypertrophic osteopathy.  

Early evaluation and detection of the condition can frequently show the root cause early enough to allow successful treatment of the underlying cause.  Since the symptoms of hypertrophic osteopathy can show up months before the symptoms of the underlying disease, early detection and treatment of the underlying cause will increase the survival chances of your beloved canine family member.