Overproduction of White Blood Cells in Cats

The eosinophils release regulatory proteins into the tissues called eosinophil-derived cytokines and eosinophil granule products. When too many eosinophils release these proteins, organ damage and death may occur.

When the bone marrow produces a greater quantity than necessary of a type of white blood cell called eosinophils, the condition is known as hypereosinophilic syndrome. White blood cells are part of the immune system and help protect the cat's body from foreign invaders and infectious diseases. When the cat becomes ill, the hematopoietic stem cells in the blood marrow produce extra white blood cells to fight these foreign invaders. Normally eosinophils make up a small portion of the white blood cell production as they are typically produced in response to parasites and allergies.

Symptom severity typically increases gradually as the number of eosinophils increase. These symptoms include:

• Loss of appetite (anorexia)
• Weight loss
• Emaciation
• Vomiting
• Diarrhea that may contain blood
• Fever
• Weakness
• Lethargy
• Enlarged liver
• Enlarged spleen
• Abdominal masses
• Thickened, non-painful intestines
• Swollen lymph nodes
• Itching
• Seizures
• Skin lesions
• Chronic cough

It is not known what causes hypereosinophilic syndrome to occur. Researchers believe that it may be caused by an overreaction to an unidentified antigen. This antigenic stimulus may arise from two different viral strains, prompting the production of white blood cells. Cats who have had eosinophilic enteritis, a disease that causes inflammation in the small intestine, may be predisposed to hypereosinophilic syndrome.

The veterinarian will need to know the cat's health history, when the symptoms first began and a detailed list of the symptoms. The veterinarian will physically examine the cat, listening to its heart and lungs and feeling for swollen lymph nodes and masses in its body.

Several labs will be performed in order to identify the condition and rule out other conditions that may present with similar symptoms. These labs include a complete blood count, a biochemical blood profile, a cytochemical staining, a fecal flotation test and a urinalysis. These tests will typically show a high number of white blood cells, anemia, and organ dysfunction in the affected organs.

A bone marrow aspiration will also be performed. The cat will be given anesthesia while the veterinarian removes a small amount of the bone marrow in order to determine what is causing the high levels of white blood cells to occur. Because blood cells are made from cells in the bone marrow, the aspiration is an important test to rule out similar conditions. The veterinarian may also biopsy the lymph nodes, spleen, liver or intestines. The biopsy can be particularly helpful in distinguishing the condition from eosinophilic leukemia. During the biopsy, the cat will be placed under general anesthesia while a small sample of tissue is removed from the organs.

Radiography may also be used to look at the condition of the affected organs. A special radiocontrast dye will be injected into the cat. Computed tomography (CT) scans and X-rays will then be taken. These tests may show thickened intestines, abnormal intestinal lining, fibrosis, coagulation of the heart arteries and enlarged lymph nodes.

Medication

Steroids, such as prednisone or prednisolone, will be administered to the cat. Steroids will help to stop the production of eosinophils. Hydroxyurea, an antineoplastic drug, may also be administered. Hydroxyurea can also slow down the production of eosinophils, allowing the immunoglobulin concentrations to normalize and the organs to heal. If these medications are no longer working, the veterinarian may start the cat on chemotherapy, which can slow the reproduction of the white blood cells by inhibiting the DNA synthesis process.

Fluid Therapy

Cats who are dehydrated will need to receive intravenous fluids to correct fluid loss due to diarrhea or vomiting. The veterinarian will keep a close watch on the affected organs during fluid therapy to ensure that the kidneys and heart are processing the fluids normally.

Nutritional Support

If the cat refuses food, nutritional support will need to be administered to ensure that the cat is receiving adequate calories for healing. A feeding tube may be inserted through the cat's nose in order to deliver this nutrition.

Though medications normally work to resolve the overproduction of the white blood cells, they may lose their effectiveness over time. With treatment, cats typically live six months to three years after diagnosis. The cat will need to regularly follow up with the veterinarian in order to monitor its blood count levels and medication effectiveness. Because the prescribed medications have side effects, it's important to take note of any side effects the cat is experiencing in order to adjust medications accordingly.