Posted on March 29, 2015
Multiple myeloma is a cancerous process that dogs, cats, and people happen to share in common. This disease is also referred to as myeloma and plasma cell myeloma. It is relatively uncommon in dogs and rare in cats. Although not considered curable, myeloma can be successfully treated.
What is multiple myeloma?
Multiple myeloma cells originate from lymphocytes, a normal type of white blood cell that resides in the bone marrow. These lymphocytes differentiate into a variety of different types of cells, one of which is the plasma cell, an important component of the body’s immune system.
In cases of multiple myeloma, plasma cells developing within the bone marrow undergo a malignant transformation, and way too many plasma cells are manufactured. This results in a “crowding out” of the normal bone marrow production of infection fighting white blood cells, oxygen carrying red blood cells, and platelets, the cells responsible for controlling bleeding in the body. Myeloma patients often have dangerously low numbers of these normal cells within their bloodstream.
Once released from the bone marrow, the malignant plasma cells often spread to other sites. Their favorite place to set up housekeeping is within bones where the damage caused by the cancer cells can create significant pain.
Plasma cells produce proteins called immunoglobulins that are the foot soldiers of the immune system. An overabundance of plasma cells, as is the case with multiple myeloma, translates into an overabundance of immunoglobulin found in the bloodstream. This immunoglobulin excess alters the normal viscosity or thickness of the blood, transforming its normal water-like consistency to that of syrup. This viscosity change wreaks havoc within smaller blood vessels where the blood sludges and causes damage to the tissues. This is referred to as hyperviscosity syndrome and can be life threatening, particularly if the brain is affected.
Cause of myeloma
Multiple myeloma in people has been associated with exposure to toxic chemicals present in tobacco smoke and emissions from petroleum refinery waste dumps and industrial operations.
The cause of multiple myeloma in companion animals is unknown, and there is no breed or sex predilection. Middle aged to older dogs and cats are most commonly affected.
The major symptoms associated with multiple myeloma are caused by the spread of cancer cells, hyperviscosity syndrome, and the underproduction of normal cells within the bone marrow (see explanations above). Additionally, some dogs and cats with myeloma develop hypercalcemia, a higher than normal level of calcium in the bloodstream. This hypercalcemia can produce a number of serious consequences over time, the most significant of which is kidney failure.
Because multiple myeloma cells can wreak havoc in so many ways, the symptoms associated with this disease vary from patient to patient. Most commonly reported symptoms include:
- Loss of appetite
- Lameness and or bone pain caused by spread of cancer cells
- Unexplained bleeding caused by inadequate platelet production or hyperviscosity syndrome
- Loss of vision caused by inadequate platelet production or hyperviscosity syndrome
- Abrupt onset of neurological symptoms or seizures caused by hyperviscosity syndrome
- Increased thirst and urine output caused by hypercalcemia
The diagnosis of multiple myeloma is made when two or more of the following criteria are satisfied:
- Radiographs (x-rays) document characteristic bony changes caused by the spread of myeloma.
- Bone marrow analysis reveals an overabundance of plasma cells.
- Protein electrophoresis results demonstrate a monoclonal gammopathy. Protein electrophoresis is a laboratory test that detects the types of immunoglobulins circulating within the bloodstream. Normal blood contains several types. Blood from a multiple myeloma patient contains an overabundance of strictly one type produced by the cancerous population of plasma cells. This “monoclonal gammopathy” is characteristic of multiple myeloma.
- The patient’s urine contains Bence-Jones proteins, a characteristic type of immunoglobulin (protein) produced by many dogs and cats with multiple myeloma.
A battery of tests is typically performed to make the diagnosis as well as to evaluate the patient’s overall health. In addition to a thorough physical examination, testing may include:
- A complete blood cell count, chemistry profile, and urinalysis
- Full body radiographs
- Abdominal ultrasound
- Bone marrow collection and evaluation
- Protein electrophoresis (performed on blood sample)
- Screening for Bence-Jones proteins (performed on urine sample)
The key to successful treatment of multiple myeloma is getting therapy started as soon as possible, so as to eliminate the excess plasma cells before they manage to cause a life-threatening problem such as a stroke, hemorrhage, infection, or kidney failure. Whenever possible, it is ideal for myeloma therapy to be initiated by a veterinarian who specializes in oncology or internal medicine. Such specialists have significantly more experience treating this relatively uncommon disease.
Chemotherapy: The mainstay of multiple myeloma treatment is chemotherapy. Chemotherapy refers to medication that is absorbed systemically, therefore fights cancer cells throughout the body. The most commonly used medications to treat myeloma are administered orally at home. They are typically well tolerated, but relatively frequent monitoring, including physical examinations and blood testing, is required. The drug dosages are adjusted up or down based on trends in the patient’s blood test results.
The chemotherapy most commonly employed to treat myeloma consists of a combination of two drugs- melphalan and prednisone. Melphalan is typically continued lifelong, and the prednisone is tapered over time. If melphalan is not well tolerated, cyclophosphamide is often substituted.
Radiation therapy: Multiple myeloma cells are quite sensitive to radiation therapy. This mode of treatment can be used to rapidly diminish the pain associated with spread of the cancer to bony sites. Radiation therapy is considered palliative (providing comfort), but does not replace chemotherapy in terms of fighting the disease.
Biphosphonates: These are drugs that can be used to help manage bone pain caused by myeloma. They may also be helpful in reducing hypercalcemia (excess calcium in the bloodstream). Use of bisphosphonates is rarely warranted when chemotherapy is used.
Although multiple myeloma is not considered a curable disease, it is one of the more treatable forms of cancer. Most dogs respond well to chemotherapy with restoration of a good quality of life. In a study of 60 dogs with myeloma treated with melphalan and prednisone, 92% experienced remission (evidence of the cancer partially to completely resolved). Average survival time for these dogs was 540 days.
Have you cared for a dog or cat with multiple myeloma? If so, what was your experience like?
Nancy Kay, DVM
Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
Become a Fan of Speaking for Spot on Facebook
Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health. There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.