The most common type of plasma cell tumor is called multiple myeloma.  The cells of this tumor can be found in the bone marrow or circulating in the blood.

The symptoms an owner may notice can include lethargy, weakness, lameness, bleeding from the nose or gums, increased drinking or urination, altered level of consciousness or seizures. 

Primary treatment of multiple myeloma includes chemotherapy to decrease the number of plasma cells that are present. 

Affected dogs can potentially survive for about 1 1/2 years when treated with chemotherapy.

What is multiple myeloma?

• One major part of the body’s immune system is the white blood cell (WBC).  The function of one particular type of WBC, the plasma cell, is to make antibodies.  In a normal animal, the antibodies are produced against a foreign substance within the body, for example a virus.  The antibodies then mark the virus or other substance as “foreign” to help it be quickly eliminated by the body.  When the dividing of a certain plasma cell is uncontrolled and it develops many, many copies of itself, we consider it a plasma cell tumor.  The most common type of plasma cell tumor is called multiple myeloma.  The cells of this tumor can be found in the bone marrow or circulating in the blood.
  
• One significant problem associated with multiple myeloma is that the cancerous plasma cells produce so many antibodies, it makes the blood very viscous.  The thick blood can be hard for the heart to pump and cause heart disease and decreased delivery of oxygen to tissues.  The large quantity of antibodies can also cause damage within the kidneys and the eyes, and prevent normal clotting.  If the body is using all its energy and resources to produce these plasma cells, it does not have as many resources to make healthy WBC’s.  Therefore, patients with multiple myeloma are more likely to develop serious infections. 
  

Clinical Signs

• Multiple myeloma is much more common in dogs than in cats, and seems to occur mostly in older pets. 
• The symptoms an owner may notice can include lethargy, weakness, lameness, bleeding from the nose or gums, increased drinking or urination, altered level of consciousness or seizures. 
• Cats often will have indistinct clinical signs of refusing to eat and weight loss. 

Diagnosis

• Your veterinarian may choose to perform a CBC, serum chemistry panel, special bloodwork to look for the presence of antibodies, urinalysis, x-rays of the chest and possibly the limbs. 
• Definitive diagnosis requires bone marrow aspirate or biopsy with analysis of the sample by a pathologist, however, the previously mentioned tests may give the doctor a high suspicion of multiple myeloma.
  

Treatment

• Primary treatment of multiple myeloma includes chemotherapy to decrease the number of plasma cells that are present.  The medication is orally administered and requires regular monitoring of your pet’s CBC with your veterinarian.  Although the treatment is highly effective and most animals become free of symptoms, eventual relapse of the disease is expected.  Your veterinarian will want to monitor your pet’s response to treatment as well.  This can be completed with repeated x-rays of the limbs, bloodwork, or urinalysis.
  
• Secondary treatment for the complications of multiple myeloma is sometimes indicated as well.  For instance, if your pet has viscous blood from the high number of antibodies, whole blood can be removed from your pet and the plasma with its antibodies removed.  The red blood cells can then be returned via transfusion.  If your pet has experienced damage to its kidneys, hospitalization with intravenous (IV) fluid therapy will be indicated. 
• If your pet has a decreased clotting ability, a transfusion of plasma can be helpful in preventing future bleeding.  Because pets with multiple myeloma have a higher risk of developing infections, preventative antibiotic therapy may be used.
  
• If your pet does not respond to the initial treatment, other medications are available.  These medications are also useful for patients that relapse with disease.  Unfortunately, most animals do not have as good of a response or as long of a period of remission as they initially would. 

Prognosis

• The prognosis for dogs with multiple myeloma with good initial control and return to a good quality of life is about 1 ½ years.  If complications occur secondary to the multiple myeloma, the prognosis decreases with the severity of that disease.  The prognosis for cats with multiple myeloma is not as favorable as it is for dogs.

References

• Small Animal Clinical Oncology:  Third Edition. Withrow, Stephen J., DVM, and E. Gregory MacEwen, VMD.  Philadelphia, PA:  W.B. Saunders Company, 2001.
  
• Textbook of Veterinary Internal Medicine:  Fifth Edition. Editors:  Ettinger, Stephen J., DVM, and Edward C. Feldman, DVM.  Philadelphia, PA:  W.B. Saunders Company, 2000.