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

Investigation typically begins with a clinical examination and a review of the patterns noticed at home—changes in energy, mobility, thirst, or unexplained bruising. Blood tests often reveal abnormalities that prompt further exploration, particularly when a characteristic protein pattern appears alongside anaemia or changes in kidney values. Imaging and bone marrow examination may follow, building a picture of whether plasma cells have expanded within the marrow and whether bone lesions are present.

Serum protein electrophoresis

Purpose: This test separates blood proteins by size and charge, revealing whether a single type of immunoglobulin is present in abnormally high amounts—a sharp peak on the trace, termed a monoclonal gammopathy. The pattern suggests clonal expansion of plasma cells.
Considerations: A monoclonal spike can occasionally appear in other conditions, including some chronic infections or immune-mediated processes, so the finding prompts further investigation rather than confirming the diagnosis alone. The test does not distinguish between different causes of clonal protein production.

Bone marrow cytology or biopsy

Purpose: Examination of marrow aspirates or core samples allows direct assessment of plasma cell numbers and appearance. In multiple myeloma, plasma cells typically comprise a much larger proportion of marrow cells than normal, often exceeding twenty per cent.
Considerations: The procedure requires sedation or general anaesthesia and sampling from the humerus, ilium, or femur. Marrow distribution can be patchy, so a single sample may occasionally underrepresent the extent of involvement. Interpretation depends on both the proportion and morphology of plasma cells.

Radiography

Purpose: Plain radiographs of the skeleton may reveal lytic lesions—discrete areas of bone loss caused by local plasma cell infiltration and osteoclast activation. These appear as punched-out radiolucent zones, most commonly in the skull, vertebrae, ribs, and long bones.
Considerations: Not all animals with multiple myeloma develop visible bone lesions, and early or diffuse marrow involvement may not be apparent on radiographs. Advanced imaging such as computed tomography or magnetic resonance imaging can detect lesions not visible on plain films, though availability and cost vary.

Urine protein electrophoresis

Purpose: Abnormal light chains produced by the clonal plasma cells may be filtered into urine and detected as Bence Jones proteins. Their presence supports the diagnosis and indicates that the kidneys are being exposed to these potentially damaging molecules.
Considerations: Collection of an adequate urine sample can be challenging in some animals, and not all cases produce detectable urinary light chains. The test is often performed alongside serum electrophoresis to build a fuller picture of protein abnormalities.

Blood biochemistry and haematology

Purpose: Routine blood tests often reveal anaemia, elevated total protein with altered globulin fractions, hypercalcaemia, and markers of kidney impairment such as raised creatinine or urea. These findings together can suggest plasma cell dyscrasia before more specific tests are performed.
Considerations: The abnormalities are not unique to multiple myeloma and can overlap with other conditions affecting older dogs, including chronic kidney disease, other tumours, or inflammatory disorders. The pattern of changes guides the choice of follow-up tests.

Options & trade-offs

Management typically combines approaches that aim to reduce the burden of abnormal plasma cells, support organ function, and address specific complications such as hypercalcaemia or anaemia. The combination chosen depends on the individual animal's overall health, the extent of organ involvement, and what is practical within the household. No single pathway suits every case, and the trajectory can vary considerably even when similar approaches are used.

Chemotherapy protocols

Combinations of alkylating agents such as melphalan or cyclophosphamide, often given alongside corticosteroids like prednisolone, can reduce plasma cell numbers and lower the production of abnormal proteins. Protocols are usually administered in cycles over weeks to months, with dosing adjusted according to blood counts and response. Some protocols are oral and can be given at home, whilst others require periodic hospital visits.

Trade-offs: Chemotherapy carries the risk of bone marrow suppression, gastrointestinal upset, and increased susceptibility to infection. Monitoring through regular blood tests is necessary, and not all animals tolerate the drugs equally well. Response varies—some individuals experience prolonged periods of stability, whilst others show limited or transient improvement.

Supportive care for organ complications

Management of kidney impairment may involve fluid therapy, dietary modification to reduce protein load on the kidneys, and medications to control secondary effects such as nausea or high blood pressure. Hypercalcaemia can be addressed with fluids, bisphosphonates, or corticosteroids. Anaemia may be managed with supportive care or, in some cases, blood transfusion if severe.

Trade-offs: Supportive measures do not reduce the plasma cell burden itself and are typically used alongside other approaches or when more targeted treatment is not feasible. The degree of kidney damage already present at diagnosis influences how much function can be preserved.

Radiation therapy for localised lesions

When plasma cell tumours cause pain or structural compromise in specific bones, targeted radiation can reduce the local tumour mass and provide relief. This approach is particularly relevant when a solitary lesion is causing lameness or spinal cord compression.

Trade-offs: Radiation requires referral to a specialist centre, involves general anaesthesia for each session, and addresses only the treated site—it does not control disease elsewhere in the marrow. Availability and cost can be limiting factors for many owners.

Monitoring without immediate intervention

In animals with minimal clinical signs and only mild laboratory abnormalities, some owners and veterinary teams choose to monitor closely with repeat blood work and imaging rather than starting active treatment straight away. This approach allows time to observe the pace of progression and defer treatment-related side effects until signs worsen.

Trade-offs: The window for effective intervention may narrow as disease progresses, and some complications such as kidney damage can become irreversible if left unchecked. This approach depends on the individual's stability and the availability of regular monitoring.

Palliative and quality-of-life focus

When the extent of disease or concurrent health problems make more intensive approaches unsuitable, management may centre on pain relief, nutritional support, and modifications to the home environment to maintain comfort. Corticosteroids may be used at modest doses for their anti-inflammatory and mild anti-tumour effects without the commitment to full chemotherapy protocols.

Trade-offs: This approach prioritises comfort over altering disease course and may result in a shorter overall time, though it can avoid the burden of frequent hospital visits and treatment side effects. The emphasis is on preserving quality during the time available.

Common misconceptions

Misconception:

"Multiple myeloma is always painful and animals suffer greatly from the moment of diagnosis."

Reality:

Pain is not universal and depends largely on whether bone lesions are present and their location. Some animals show minimal discomfort, particularly early in the course or when lesions are absent or small. Pain management, when needed, can often provide substantial relief and is tailored to the individual.

Misconception:

"Chemotherapy for multiple myeloma is as intensive and debilitating as chemotherapy protocols used in human oncology."

Reality:

Veterinary chemotherapy protocols typically use lower doses than those in human medicine, with the goal of managing disease whilst preserving quality of life rather than pursuing cure at any cost. Most dogs tolerate oral chemotherapy at home with minimal side effects, though monitoring remains necessary. The experience varies between individuals, and some do develop gastrointestinal upset or bone marrow suppression that requires dose adjustment.

Misconception:

"If blood tests and imaging are normal at one point, multiple myeloma can be ruled out permanently."

Reality:

The condition develops gradually, and early stages may not produce detectable abnormalities. A single normal set of results reflects the status at that moment, but does not exclude the possibility of changes emerging later. Repeat testing may be warranted if clinical signs evolve or new abnormalities appear.

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.

Understanding how plasma cell behaviour intersects with kidney function, bone health, and the immune response can provide context for the range of signs that may appear over time. Exploring the broader topic of how age-related changes in immune regulation influence the development of clonal cell populations may be useful. The patterns observed in this condition also overlap with other causes of monoclonal protein production and bone marrow disorders, which form part of the differential picture in older animals presenting with unexplained anaemia or hypercalcaemia.