Multiple Myeloma in Dogs

What Is Multiple Myeloma In Dogs?

Multiple myeloma is a cancer arising from plasma cells. Plasma cells are normal cells in animals’ bodies that are responsible for producing antibodies and other proteins which help to fight off infection and disease. When these cells become abnormal and accumulate in the bone marrow, they can cause damage to healthy tissue and interfere with normal blood cell production. Multiple myeloma is characterized by an abnormal production of malignant plasma cells also known as plasma cell neoplasia. Solitary plasmacytoma is a type of plasma cell cancer that affects a single area or location oftentimes, a dermal (skin) mass or oral mass. This sets it apart from multiple myeloma, which is a widespread, systemic cancer that affects multiple areas of the body. At times, solitary plasmacytoma precedes multiple myeloma.

Identifying Canine Multiple Myeloma

To diagnose multiple myeloma, at least three of the following defining features must be present.

1. Monoclonal gammopathy is a term used to describe an excess of an immune protein from a single clone of cells. A monoclonal gammopathy is typically found in multiple myeloma. The presence of this excessive protein accumulation can indicate malignant changes in the bone marrow and cancerous plasma cells that are interfering with the body’s ability to fight off infection and disease. Monoclonal gammopathy is usually detected through a blood test called a protein electrophoresis.
2. Plasmacytosis is characterized by the presence of a high number (>10-20%) of plasma cells within the bone marrow. Cancerous plasma cells are usually confirmed by bone marrow aspirate and is one of the defining characteristics of multiple myeloma. Plasmacytosis in the bone marrow can lead to damaging and reducing red blood cell production (anemia), white blood cell production (leucopenia) and platelet production (thrombocytopenia) .
3. Lytic bone lesions are areas of destruction in the bones caused by multiple myeloma. These lesions can cause pain or lameness as well as other symptoms such as fever, lethargy, anorexia, and weight loss. Lytic bone lesions can also lead to fractures due to the weakened bone structure. Radiographs and CTs are often used to detect these lesions.
4. Proteinuria, in multiple myeloma, is due to a specific type of light chain protein, called Bence-Jones proteins. Bence-Jones proteins can be found in the urine of multiple myeloma patients when there is an abnormally high number of malignant plasma cells present.
5. Excessive plasma cell infiltrate in affected organs such as the spleen, liver and lymph nodes. At times, this will cause enlargement of these organs. These can be found via ultrasound-guided aspiration cytology.
6. Hypercalcemia is found in a portion of patients with multiple myeloma. Patients will have abnormally high levels of calcium. This can cause excessive urination and hence excessive thirst. Long term, hypercalcemia can cause irreparable damage to the kidneys which can result in kidney insufficiency or even kidney failure.

What Causes Multiple Myeloma In Dogs?

The exact cause of multiple myeloma in dogs is unknown, but researchers believe that certain environmental factors like exposure to radiation or toxins can increase the risk of developing the condition. In dogs, age appears to be a major factor in development; older dogs are more likely to be afflicted with the condition. Certain breeds of dogs, such as German Shepherds, may also have an increased risk over mixed-breed dogs.

Symptoms Of Multiple Myeloma In Dogs

The signs and symptoms of multiple myeloma vary greatly from case to case and depend on the part of the dog’s body where it is found. At times, the initial clinical signs and test results for lymphoma can be hard to distinguish from this disease. Depending on the location, a wide variety of signs and symptoms are often seen in multiple myeloma including:

  • Lethargy
  • Weight loss
  • Poor appetite
  • Vomiting and/or diarrhea
  • Pale gums due to anemia
  • Increased thirst and urination
  • Dehydration
  • Fever
  • Infections that may not respond to treatment
  • Lameness due to pain in the bones affected by the malignant cells
  • Bleeding
    • Excessive from site where blood is drawn
    • From areas in the head including eyes, nose and mouth- sometimes seen as very small, red dots known as petechiation
    • In the gastrointestinal tract (may have dark/bloody stool)
  • Enlarged liver or spleen, sometimes showing as a pot-bellied appearance
  • Eye issues
    • Glaucoma
    • Detached retina
    • Bleeding behind the eyes
    • Blindness
  • Hyper-viscosity syndrome is caused by excessive proteins and results in a thickness to the blood which can lead to seizures, vision issues, dementia and cardiac issues.

Diagnosing And Staging Canine Multiple Myeloma

Because the symptoms for multiple myeloma vary widely and oftentimes resemble a whole host of other diseases, your veterinarian will need to take a deep dive into your dog’s health history, current symptoms, and diagnostics. Your veterinarian may need to exclude another disease to properly diagnose your dog.

Diagnosing multiple myeloma typically includes:

  • A thorough health history of your dog
  • Complete blood count which will be able to identify any abnormalities in the red blood cells, white blood cells or platelets.
  • Chemistry profile to assess total protein levels, kidney function, liver function, etc.
  • Urinalysis to help assess kidney function
  • Protein electrophoresis to assess if the elevation in proteins is due to one specific band (monoclonal gammopathy) or from many bands (polyclonal gammopathy).
  • Bence-Jones assay on the urine to assess for light chain proteins
  • Bone marrow aspirate is used to look for the percentage of cells that are plasma cells within the marrow.
  • Imaging such as 3-view chest/abdominal X-rays and/or CT to asses for bony lesions.
  • Abdominal ultrasound with aspiration cytology is important to assess for any signs of malignancy in the internal organs.

Once diagnosed, the disease is staged based on the number of malignant plasma cells present in the bone marrow and where they have spread in the body.

What Are The Treatment Options For Dogs With Multiple Myeloma?

Treatment options for multiple myeloma vary depending on the stage and severity of the condition. The most common treatment is chemotherapy. The main chemotherapy protocol for this disease is often a combination of pills (melphalan with prednisone) given orally on an every other day basis. At times, radiation therapy can be used to help reduce bone pain, to target local areas of disease or for dogs with solitary plasmacytomas. Surgery may also be employed for solitary plasmacytomas. Dogs with multiple myeloma may also benefit from supportive therapies such as pain medication, bisphosphonates, nutritional therapy, renal (kidney) support, and acupuncture.

What Is The Prognosis For Dogs With Multiple Myeloma?

The prognosis for dogs with multiple myeloma depends on the stage and severity of the condition as well as how quickly treatment can be started. Many dogs respond very well to treatment and have a good quality of life for an extended period of time (1-2 years) while others may only have a few months or less. In general, early detection and prompt treatment can improve the chances of a positive outcome and extend life expectancy in affected pets.

While there is no way to protect your dog from multiple myeloma, it is always best way schedule regular veterinary check-ups. Knowing the signs and symptoms of multiple myeloma can also help you to detect it early if it does occur. If your dog is showing any of the above-mentioned signs, contact your veterinarian right away for an evaluation. With quick diagnosis and treatment, your pet may be able to lead a longer, healthier life.

If your dog has been diagnosed with multiple myeloma, we invite you to reach out to PetCure Oncology’s Pet Advocate Team to get the information you need. Our pet advocates help pet cancer patients understand their diagnosis and it’s a complimentary service we offer to help you in your cancer journey toward healing.

Types of Cancers in Dogs

If your dog is displaying any symptoms of cancer or has been diagnosed with cancer, sort below by cancer type or tumor location to learn more about the most common types of cancer in dogs and available treatment options. Click on the links for more specific information on treatment and real patient stories.


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