What You Should Know About Bone Marrow Cancer in Dogs

We tend to take bone marrow for granted -- that is, until it goes wrong.

Bone marrow works away in the background, manufacturing blood cells that are essential for life. But if it produces too many of one type of blood cell called a “plasma cell,” this is a form of cancer known as myeloma.

The good news is, this is a rare condition. Myeloma makes up only 1% of all the most serious malignant cancers.

Symptoms

Plasma cells produce infection-fighting proteins called “immunoglobulins,” which are essential to a healthy immune system.

Unfortunately, dogs with myeloma produce too much of this protein, which thickens the blood and makes it too sticky to pass easily through blood vessels.

This is a bit like making a cordial drink -- a small amount of cordial and a lot of water makes for a refreshing drink, but all cordial and no water is thick, sticky and undrinkable. This thick blood, full of protein, may soon prompt kidney failure.

Bone marrow is so preoccupied with producing plasma cells that it neglects to make platelets, which are vital for blood clotting. This means a dog with myeloma is prone to bleed from minor cuts and scratches, and may suffer from nosebleeds or show blood in his urine.

Sometimes, overactive bone marrow causes bone pain, and the dog is uncomfortable, restless and limps. Symptoms of myeloma: Lameness (from bone pain) Prolonged bleeding from minor wounds Sudden blindness (due to bleeding inside the eye) Thirst Weight loss and poor coat condition Fever

Causes

There is no known cause for bone marrow cancer.

The condition is rare and tends to occur in middle-aged or old dogs.

German Shepherds account for more than their fair share of cases.

Diagnosis

As with so many veterinary conditions, diagnosing myeloma requires detective work.

A specialized test looks for specific proteins in the urine that are the “signature” of myeloma. This sounds straightforward until you appreciate that these “Bence-Jones” proteins are only present in 30 to 40% of cases -- a negative result may be misleading.

The clinician looks for hints on screening blood tests such as anemia, low platelet numbers and raised calcium levels. Another clue is an abnormal balance of blood protein levels, and kidney or liver damage.

If your vet is suspicious of myeloma and the dog is lame, radiographs may show typical “punch hole” patterns in the long bones, which are characteristic of myeloma, but frustratingly are not present in every case. A definitive diagnosis is made on bone marrow biopsy.

Treatment

Thick blood causes damage as it is forced through organs, and so the first step is to thin the blood with intravenous fluids.

While chemotherapy is not a cure, some dogs show encouraging improvements and go into long-term remission. This treatment usually involves taking pills regularly. However, these drugs suppress already-weak immune systems and make the patient more vulnerable to infection.

Any dog in treatment for myeloma needs careful monitoring for signs of infection, such as coughing, sneezing or tummy upsets.

Prevention

Sadly, at the present time, there is no known preventative treatment for this cancer.

References

• The Five-Minute Veterinary Consult. Tilley, Francis & Smith. Publ: Williams and Wilkins.
• Small Animal Internal Medicine. Nelson & Couto. Publ: Mosby. 5th edition.
• “Hematopoietic tumors.” MacEwan & Young. Clinical Veterinary Oncology. 1989: 402–411.

This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.