CONDITION
Multiple Myeloma
Multiple myeloma is a condition in which a type of white blood cell called a plasma cell begins to multiply abnormally in the bone marrow. These cells can crowd out healthy blood cells and produce abnormal proteins that circulate in the blood and may be filtered into the urine. The condition tends to affect older dogs more commonly than cats, and it develops gradually. Owners often notice signs that can seem unrelated at first—lethargy, weakness, increased thirst, or lameness that may come and go. Some dogs develop nosebleeds or bruise more easily. In other cases, the condition is detected through routine blood work before any outward signs appear. The variety of possible presentations reflects the different ways these abnormal cells and their proteins can affect the body. This page explores what signs may prompt investigation, the mechanisms by which plasma cells behave this way, how the condition is identified through blood tests and imaging, and the range of approaches that exist to manage it. The course and outlook vary considerably between individuals.
Why this matters now
Multiple myeloma tends to appear in older dogs, typically those beyond eight years of age, though the precise timing varies between individuals. Certain breeds may be represented more frequently in case series, though the condition can develop in any dog. Cats are affected far less commonly, and when the condition does occur in feline patients, it often follows a similar age pattern. No single environmental or nutritional factor has been clearly linked to its development.
The condition typically develops gradually over months, with signs accumulating as abnormal plasma cells multiply and their effects on the bone marrow and other tissues become more pronounced. Some dogs show subtle changes in energy or mobility long before blood work reveals the underlying process. The pace of progression can vary considerably—some individuals deteriorate relatively quickly, whilst others may have a more protracted course with periods of apparent stability. The pattern reflects both the behaviour of the abnormal cells and how the body responds to their presence.
Signals & patterns
Early signals
Reduced stamina or energy
An owner may notice that their dog tires more easily on familiar walks or seems less interested in activities they previously enjoyed. This can reflect anaemia developing as abnormal plasma cells crowd out the cells responsible for producing red blood cells in the bone marrow.
Intermittent lameness or stiffness
A dog may favour one leg or appear reluctant to jump or climb stairs, with the discomfort sometimes shifting from one limb to another. This pattern can occur when plasma cells accumulate in bone, weakening it or triggering localised inflammation and pain.
Increased drinking and urination
The abnormal proteins produced by myeloma cells can interfere with normal kidney function, prompting the body to produce larger volumes of dilute urine. Owners often notice the water bowl needing refilling more frequently and more frequent requests to go outside.
Weight loss despite normal appetite
A dog may continue to eat as usual but gradually lose body condition over weeks to months. The metabolic demands of the proliferating plasma cells and the effects of abnormal proteins on nutrient processing can both contribute to this pattern.
Occasional nosebleeds or bruising
Small bleeding episodes can occur when abnormal proteins interfere with normal blood clotting or when the bone marrow's capacity to produce platelets is reduced. These signs may be noticed as spots of blood on bedding or unexplained bruises under the skin.
Later signals
Visible swelling over bones
Firm lumps may become palpable over the ribs, skull, or long bones of the limbs as plasma cell tumours expand within or around the bone. These areas may or may not be painful to the touch.
Marked weakness or collapse
As anaemia worsens or if calcium levels in the blood become significantly elevated due to bone breakdown, a dog may struggle to stand or appear profoundly weak. This reflects the compounded effects of reduced oxygen delivery and metabolic disturbance.
Difficulty breathing or exercise intolerance
Severe anaemia or, less commonly, thickening of the blood due to high levels of abnormal protein can reduce the efficiency with which oxygen reaches tissues. Owners may notice panting at rest or an unwillingness to move even short distances.
Neurological changes
In some cases, abnormal proteins can affect blood flow to the brain or plasma cells can invade the spinal column, leading to confusion, unsteadiness, or weakness in the hind limbs. These signs indicate more advanced involvement of the nervous system.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
Related conditions
Plasmacytoma
Plasmacytoma is also a tumour arising from plasma cells, but typically appears as a solitary growth in the skin or mouth rather than within the bone marrow. In some cases, a solitary plasmacytoma can progress over time to involve multiple sites in a pattern more characteristic of multiple myeloma.
Multicentric Lymphoma in Dogs
Both multiple myeloma and multicentric lymphoma involve uncontrolled proliferation of white blood cells—plasma cells in myeloma and lymphocytes in lymphoma—and both can cause similar clinical signs such as lethargy, weight loss, and enlarged lymph nodes, though the cell types and patterns of spread differ.
Osteosarcoma in Dogs
Osteosarcoma and multiple myeloma can both present with lameness and bone pain, and imaging may show bone changes in either condition. The key distinction lies in where the abnormal cells originate—bone-forming cells in osteosarcoma versus plasma cells in the marrow in myeloma.
Glomerulonephritis
The abnormal proteins produced by plasma cells in multiple myeloma can sometimes be deposited in the kidney's filtering units, contributing to glomerular damage and protein loss in the urine, a pattern that overlaps with other causes of glomerulonephritis.
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