Hypereosinophilic syndrome is a disorder which is the result of overproduction of white blood cells in the bone marrow in dogs. It can occur spontaneously and the exact cause is not known.  It is characterized by an increased number of eosinophils in the dog’s blood, and can possibly occur due to the response to certain drugs, parasites, or allergens. This blood disorder is known to lead to hepatitis and other abnormal organ function. Abnormal organ function is the result of the eosinophils permeating into the tissues. Organs and organ systems which are often affected are the spleen, lungs, lymph nodes, gastrointestinal tract, and bone marrow.

Overproduction of white blood cells in the bone marrow in dogs, or hypereosinophilic syndrome, is the abnormally high amount of eosinophils, or white blood cells, in the blood of dogs. This results in organ damage with an overpopulation of the eosinophils within organ tissue.

If your dog is exhibiting any symptoms that may point to hmi feeling unwell,  or if you are seeing behavioral changes, it is very important to make an appointment with the veterinarian. Symptoms of overproduction of white blood cells in the bone marrow in dogs include:

Although this rare illness can occur in any dog breed, either purebred or mixed, this disorder is known to be more prevalent in specific dog breeds. The breeds that are predisposed to an overproduction of white blood cells in the bone marrow are:

The precise cause of hypereosinophilic syndrome is unknown. Research is underway in an attempt to learn more about this rare condition, which affects both humans and canines. What is known is that the white blood cell (called the eosinophil), present in the circulating blood, is much higher in number than normal. These cells may also penetrate tissues, causing organ involvement in the form of thickening of tissues (such as in the spleen, gastrointestinal tract, and lungs).

Your veterinarian will listen to your concerns and ask questions about the onset and severity of the symptoms. He will take a look at the dog’s health history as well. The first plan of action will be to do a complete blood test, to check for hypereosinophilia. If marked increase in the white blood cells is present, the veterinarian will perform a bone marrow biopsy to reveal the condition even further. The medical professional may conduct a test with a bronchoscope, called a bronchoalveolar lavage, analyzing a fluid collected after insertion into the lungs, which will then be tested for the increased quantities of eosinophils. Biopsies of several different organs will also be conducted.

Other tests, including cytogenetic analysis, serum analysis, and biochemistry may be also performed, mainly to differentiate this illness from leukemia. The veterinarian will also need to rule out fungal infections, eosinophilic cellulitis, mast cell tumors, eosinophilic bronchopneumopathy, parasitic infections, and eosinophilic enteritis.

Treatment will require long-term dedication to therapy in helping reduce the abnormal white blood cell count and treating any organ damage. Methods include:

Prednisone may be given to reduce inflammation and grant the dog a much better prognosis in the long term. 

In some cases, chemotherapy medications may be successful by suppressing the reproduction of white blood cells.

Depending on the treatment given, the doctor will have instructions for you to follow in terms of after-care and therapy. Routine veterinary visits will be required in order to monitor the dog’s production of white blood cells and to also monitor the damaged organs to see if they are improving. It will be important to monitor side-effects from the therapy given, and prognosis of this disorder varies greatly on the amount of eosinophil infiltration into the affected organ tissue.