Multiple myeloma is a cancer of plasma cells, which develop from a type of white blood cell called a B cell. Plasma cells produce antibodies, which are used by the body to fight infections. In patients that develop multiple myeloma, these plasma cells multiply uncontrollably.
Multiple myeloma is rare in cats and dogs. Scientists have not yet been able to discover why this type of cancer occurs. Potential factors that lead to a pet developing multiple myeloma are genetics or inheritance from a parent, certain viral infections, exposure to carcinogens, and continual stimulation of the immune system (for example, having a chronic illness).
When multiple myeloma occurs, the number of plasma cells increase unchecked. They are created in the bone marrow, so typically over time, their overproduction crowds out other cells made in the bone marrow such as other types of white blood cells, red blood cells, and platelets. This form of multiple myeloma is the classic appearance in people and dogs. Cats may also develop this form of the disease, but more often develop plasma cell cancer in organs outside the bone marrow, such as the liver or spleen.
Secondary diseases, sometimes known as paraneoplastic syndromes, are common with multiple myeloma. Many of these occur because of changes in the immune system caused by plasma cell overproduction. Examples include renal/kidney disease, elevated calcium levels, bone loss (also known as osteolysis), decreased immune function, bleeding disorders, and increased blood thickness (known as hyperviscosity syndrome).
Symptoms include acting tired and/or weak, vomiting or throwing up, loose stools, and not wanting to eat. Unfortunately, many other issues can cause these symptoms as well, so at first it may be difficult to figure out what is wrong with your pet. Drinking and urinating a lot, trouble walking, and signs of bleeding (e.g. nosebleeds, bleeding gums, pale skin, bruising) may also be seen.
Because symptoms don’t point directly to the issue, different types of testing are needed to diagnose multiple myeloma. A blood test to evaluate how the red blood cells, white blood cells, and platelets are functioning, called a CBC or complete blood count, may be performed. Another blood test called a serum biochemistry or biochemistry profile is also commonly used. It gives the veterinarian information on how the internal organs are functioning. In multiple myeloma and a few other diseases, the globulin level (a type of protein) is usually increased. Serum biochemistry test will give information about the globulin level as well. Additional lab tests may include some for bleeding irregularities, urine testing, and a test to assess certain proteins in the blood, known as serum protein electrophoresis. X-rays, ultrasound, and bone marrow aspiration or biopsy are frequently done as well.
Treatments are available for multiple myeloma, but cure is rare. That being said, treatments used will help the pet feel better, with improvement in symptoms noted within a few weeks of starting therapy. Average survival times once a pet is diagnosed are 220-930 days in dogs (depending on which treatments are used) and 42-281 days for cats. Pets that do not receive any treatments do not live as long as most pets that are treated, but how long they can live without treatment is not clear.
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