Multiple Myeloma and Plasma Cell Tumours in Cats: Signs, Diagnosis and Treatment

Multiple Myeloma and Plasma Cell Tumours in Cats: Signs, Diagnosis and Treatment

By Dr Duncan Houston

A cat with lethargy, weight loss and very high globulin levels may have infection, inflammation, lymphoma or several other diseases. Less commonly, the underlying problem is a cancer of the plasma cells.

Plasma cell cancers are particularly confusing in cats because they do not always behave like classic multiple myeloma in dogs or people. Some cats have obvious bone marrow disease. Others have extensive involvement of the liver or spleen with only small numbers of abnormal plasma cells in the bone marrow.

The important questions are not simply whether an abnormal protein is present. They are where the cancerous cells are located, whether the blood has become dangerously viscous, whether the kidneys or bone marrow are being damaged and which treatment is most likely to preserve quality of life.

Quick Answer

Myeloma-related disorders are rare cancers involving plasma cells or closely related antibody-producing cells. Cats may develop bone marrow disease, liver or spleen infiltration, skin tumours, solitary bone lesions or, much more rarely, plasma cell leukaemia or an IgM-producing disorder.

Warning signs include lethargy, appetite loss, weight loss, pale gums, increased thirst, vomiting, unexplained bruising, bone pain, sudden vision changes and neurological abnormalities. Diagnosis usually requires serum protein electrophoresis together with bone marrow, liver, spleen, bone or tumour sampling. Treatment may involve chemotherapy, surgery, radiation therapy and supportive care, but the prognosis varies substantially according to the form and severity of disease.

What Are Plasma Cells?

Plasma cells are specialised immune cells derived from B lymphocytes.

Their normal job is to produce antibodies, also called immunoglobulins. Antibodies help the immune system recognise and respond to infectious organisms and other foreign material.

A plasma cell becomes neoplastic when it begins dividing uncontrollably. The resulting population is usually derived from one abnormal clone and may produce large quantities of one antibody or antibody fragment.

This abnormal protein may be called:

• A paraprotein

• Monoclonal protein

• M protein

• M component

• Monoclonal immunoglobulin

The cancer can cause problems through the physical growth of tumour cells, the abnormal protein they produce or both.

What Is a Myeloma-Related Disorder?

“Myeloma-related disorder” is an umbrella term covering several cancers arising from plasma cells or immunoglobulin-producing B-cell precursors.

This broader term is particularly useful in cats because feline disease commonly involves the liver, spleen or other tissues without the extensive bone marrow involvement expected in classic multiple myeloma.

The distinction between multiple myeloma and multicentric extramedullary plasmacytoma can therefore become blurred in cats. In practice, identifying the distribution, biological behaviour and complications is often more useful than forcing every cat into one rigid category.

What Types of Myeloma-Related Disorders Occur in Cats?

Disorder	What it means	Typical pattern
Multiple myeloma	Systemic plasma cell cancer involving the bone marrow	Paraprotein production, bone marrow plasmacytosis, cytopenias and possible bone, liver or spleen involvement
Multicentric non-cutaneous extramedullary plasmacytoma	Plasma cell cancer involving internal organs without substantial marrow infiltration	Most commonly affects the spleen, liver or abdominal lymph nodes
Cutaneous extramedullary plasmacytoma	One or more plasma cell tumours within the skin	May remain localised or occur as part of systemic disease
Solitary osseous plasmacytoma	One plasma cell tumour arising within bone	May cause pain, lameness, spinal compression or pathological fracture
IgM macroglobulinaemia	A rare immunoglobulin-producing disorder dominated by IgM	Particularly associated with hyperviscosity because IgM is a large molecule
Immunoglobulin-secreting lymphoma	A B-cell or lymphoplasmacytic cancer producing a paraprotein	Can closely mimic plasma cell myeloma
Plasma cell leukaemia	Large numbers of malignant plasma cells circulating in the blood	Rare and generally aggressive

These categories are recognised in the feline literature, but several are supported by only small case series or individual reports.

How Common Is Myeloma in Cats?

Myeloma-related disorders are rare, accounting for less than 1% of feline malignancies and approximately 1.9% of haematological cancers in cats.

They are diagnosed most often in mature or senior cats. A recent multicentre study also found male cats were overrepresented, although there is no established breed predisposition that should influence routine screening.

The rarity of these cancers creates an important limitation: most feline treatment and prognosis data come from retrospective studies involving relatively small numbers of cats.

How Is Feline Myeloma Different From Myeloma in Dogs and People?

Classic multiple myeloma is usually described as a bone marrow cancer associated with numerous destructive bone lesions.

Cats frequently break that rule.

In the largest recent feline study:

• Splenic infiltration was confirmed in 86% of assessed cats

• Hepatic infiltration was confirmed in 71%

• Both liver and spleen were involved in 62%

• Bone marrow plasmacytosis was identified in 63%

• Osteolytic bone lesions were identified in 29%

Some cats therefore had extensive visceral disease despite having little or no obvious bone marrow infiltration.

This means a normal or mildly abnormal bone marrow sample does not automatically exclude a feline myeloma-related disorder. The liver and spleen may be more diagnostically useful than they would be in a dog with suspected classic multiple myeloma.

What Causes Myeloma-Related Disorders in Cats?

The cause is usually unknown.

Possible mechanisms proposed across species include:

• Accumulated genetic damage within plasma cells

• Chronic immune stimulation

• Abnormal regulation of B-cell development

• Environmental carcinogen exposure

• Inherited susceptibility

None has been established as the routine cause in cats.

Unlike some feline lymphomas and leukaemias, there is no convincing evidence that FeLV, FIV or feline infectious peritonitis routinely causes feline multiple myeloma. Retrovirus testing may still be appropriate during the work-up because these infections can cause cytopenias, immune dysfunction and other cancers that affect diagnosis and treatment.

What Are the Signs of Multiple Myeloma in Cats?

The early signs are usually vague.

In a recent study of 50 affected cats, the most frequent presenting signs were:

• Lethargy

• Reduced or absent appetite

• Weight loss

Other findings included pale gums, increased thirst and urination, dehydration, vomiting, abdominal organ enlargement, fever, recurrent respiratory infections, lameness, neurological signs, bleeding and ocular abnormalities.

Common owner-observed signs include:

• Sleeping more than usual

• Hiding

• Reduced appetite

• Complete refusal of food

• Gradual or rapid weight loss

• Muscle loss

• Weakness

• Pale gums

• Vomiting

• Increased thirst

• Larger urine clumps

• Difficulty jumping

• Lameness

• Spinal or bone pain

• Bruising

• Nosebleeds

• Blood in the mouth, urine or stool

• Recurrent infection

• Skin nodules or masses

• Swollen abdomen

• Sudden visual changes

• Abnormal behaviour or seizures

The mistake is expecting every affected cat to have bone pain or obvious tumours. Many initially present as an older cat that is simply losing weight, eating poorly and becoming progressively quieter.

Why Can Myeloma Cause So Many Different Problems?

Myeloma-related disorders can affect the body in several ways simultaneously.

Excessive Abnormal Protein

Neoplastic plasma cells may produce enormous quantities of one immunoglobulin or antibody fragment.

This can cause:

• Hyperproteinaemia

• Hyperglobulinaemia

• Rouleaux formation on a blood smear

• Hyperviscosity

• Kidney injury

• Proteinuria

• Abnormal bleeding

• Interference with normal antibody function

The serum may become physically thicker, while the abnormal protein can interfere with platelets, circulation and organ function.

Bone Marrow Infiltration

Cancerous plasma cells may replace normal bone marrow tissue.

This can reduce production of:

• Red blood cells, causing anaemia

• White blood cells, increasing infection risk

• Platelets, increasing bruising and bleeding risk

In the recent 50-cat study, anaemia was present in 67% and thrombocytopenia in 34%. Both were independently associated with shorter survival.

Liver and Spleen Infiltration

Cats frequently develop plasma cell infiltration of the liver and spleen.

This may cause:

• Organ enlargement

• Abdominal discomfort

• Liver enzyme elevations

• Reduced appetite

• Weight loss

• Abdominal fluid in some cats

• Reduced normal organ function

These organs can contain neoplastic plasma cells even when their ultrasound appearance is subtle or normal.

Bone Destruction

Myeloma cells can stimulate bone breakdown.

Possible consequences include:

• Bone pain

• Lameness

• Reluctance to jump

• Spinal pain

• Neurological deficits

• Pathological fractures

• Hypercalcaemia

Bone lesions were found in approximately 29% of cats in the recent study and commonly involved vertebrae, the pelvis, ribs and long bones. Pathological fractures were uncommon but possible.

Kidney Injury

Kidney dysfunction may develop because of:

• Immunoglobulin light-chain injury

• Protein deposition

• Dehydration

• Hypercalcaemia

• Reduced renal blood flow

• Infection

• Concurrent chronic kidney disease

Azotaemia was reported in 42% and proteinuria in 57% of assessed cats in the recent cohort. These findings are not automatically caused by myeloma, but they deserve careful investigation.

Immune Dysfunction

Although the tumour may produce a large quantity of one antibody, that antibody is usually not useful for normal immune protection.

At the same time, production of the cat’s other normal immunoglobulins may be reduced. Bone marrow disease and chemotherapy can further weaken immune defences.

Affected cats may therefore develop recurrent or unusually severe infections.

What Is Hyperviscosity Syndrome?

Hyperviscosity syndrome occurs when excessive circulating protein makes the blood abnormally thick.

This slows blood flow through small vessels and places additional strain on the eyes, brain, heart and other organs.

Possible signs include:

• Sudden blindness

• Dilated pupils

• Retinal haemorrhage

• Retinal detachment

• Seizures

• Head tilt

• Abnormal eye movements

• Confusion

• Weakness

• Collapse

• Abnormal bleeding

• Rapid breathing

• Congestive heart failure

In the recent feline cohort, hyperviscosity syndrome was clinically suspected in one-third of the cats assessed for it. Earlier reports described retinal haemorrhage, neurological signs and cardiovascular complications in affected cats.

Why are eye changes important?

The retina allows a veterinarian to see small blood vessels directly.

A dilated-eye examination may reveal:

• Enlarged and tortuous retinal vessels

• Retinal haemorrhage

• Retinal detachment

• Chorioretinal inflammation

These findings may be the first visible clue that excessive paraprotein is disrupting circulation.

Sudden blindness in a cat with severe hyperglobulinaemia is an emergency.

How Worried Should You Be?

Risk level	What you may notice	Recommended action
Suspicious but stable	Mild weight loss, reduced energy, an unexplained skin mass or increased globulins, but still eating and behaving reasonably normally	Arrange a veterinary examination and diagnostic plan within the next few days
Moderate concern	Persistent appetite loss, progressive weight loss, vomiting, increased thirst, enlarged abdominal organs or recurrent infections	Arrange assessment within 24 to 48 hours
High concern	Pale gums, significant weakness, bruising, bleeding, lameness, marked bone pain, kidney abnormalities or rapidly increasing proteins	Seek same-day veterinary assessment
Critical	Sudden blindness, seizures, collapse, breathing difficulty, uncontrolled bleeding, inability to stand or a suspected pathological fracture	Go to an emergency veterinary hospital immediately

The level of concern is determined by more than the globulin concentration. Neurological function, breathing, vision, hydration, blood-cell counts, kidney function and the cat’s ability to eat matter more when deciding whether immediate treatment is required.

How Is Myeloma Diagnosed in Cats?

There is no single test that confirms every feline myeloma-related disorder.

Diagnosis is usually built from evidence of an abnormal protein combined with evidence of a clonal plasma cell population or associated organ damage.

1. Complete Blood Count

A CBC may identify:

• Non-regenerative anaemia

• Neutropenia

• Other forms of leucopenia

• Thrombocytopenia

• Circulating plasma cells

• Rouleaux formation

Rouleaux describes red blood cells forming stacked chains. Some rouleaux can occur normally in cats, but marked rouleaux alongside severe hyperglobulinaemia increases concern about abnormal plasma proteins.

Anaemia and thrombocytopenia are particularly important because both were associated with a poorer outcome in the largest recent feline study.

2. Serum Biochemistry

Important findings may include:

• High total protein

• Markedly high globulin

• Low albumin-to-globulin ratio

• Low albumin

• Azotaemia

• Increased liver enzymes

• Hyperbilirubinaemia

• Hypercalcaemia

• Electrolyte abnormalities

A marked globulin increase is an important clue, but it is not a diagnosis.

High globulins are also seen with:

• Feline infectious peritonitis

• Chronic bacterial infection

• Fungal disease

• Immune-mediated disease

• Chronic inflammation

• Lymphoma

• Some other cancers

The pattern of proteins must be investigated rather than assuming every high globulin result represents myeloma.

3. Serum Protein Electrophoresis

Serum protein electrophoresis separates the major blood proteins according to their physical properties.

A broad increase in several immunoglobulin types is called a polyclonal gammopathy. This more commonly reflects infection, inflammation or broad immune stimulation.

A narrow, tall peak is compatible with a monoclonal gammopathy, meaning one clone is producing a large amount of one protein.

In a study of 155 cats undergoing protein electrophoresis, monoclonal gammopathy was uncommon and occurred with splenic plasmacytoma, lymphoma and feline infectious peritonitis. A monoclonal peak therefore increases suspicion of an antibody-producing cancer but does not independently confirm myeloma.

Is immunofixation different?

Immunofixation electrophoresis can help identify the type of heavy and light chains making up the paraprotein.

This may help distinguish:

• IgG

• IgA

• IgM

• Light-chain disease

• Biclonal patterns

Availability varies between veterinary laboratories.

Should serum globulin or the M protein be monitored?

When possible, treatment response should be followed by measuring the abnormal electrophoretic M-protein rather than relying only on total globulin.

Globulin contains several proteins and may change because of inflammation, hydration or other disease. Densitometric measurement of the paraprotein provides a more specific assessment of the neoplastic protein.

4. Urine Testing

Urinalysis helps assess:

• Urine concentration

• Proteinuria

• Kidney function

• Infection

• Blood

• Glucose

• Urinary sediment

A urine protein-to-creatinine ratio may be used to quantify protein loss.

What are Bence Jones proteins?

Bence Jones proteins are monoclonal immunoglobulin light chains that pass into the urine.

They support a diagnosis of myeloma-related disease and may directly damage the kidneys.

Modern assessment may involve:

• Urine protein electrophoresis

• Urine immunofixation

• Other laboratory methods for identifying immunoglobulin light chains

Only 47% of tested cats in the recent cohort had detectable Bence Jones proteinuria, so a negative result does not exclude myeloma.

5. Bone Marrow Aspiration and Biopsy

Bone marrow sampling may be recommended when:

• Anaemia is present

• White blood cells are reduced

• Platelets are low

• Multiple myeloma is suspected

• Circulating abnormal cells are seen

• The distribution of the disease remains uncertain

The pathologist assesses:

• Percentage of plasma cells

• Cellular appearance

• Degree of atypia

• Replacement of normal marrow

• Other blood-cell precursors

• Evidence of lymphoma, leukaemia or infection

Normal feline marrow usually contains fewer than 5% plasma cells. A high percentage strongly supports myeloma, but small numbers of markedly atypical plasma cells can also be significant.

Can a normal bone marrow result rule out feline myeloma?

No.

Plasma cell infiltration may be patchy, and cats frequently develop liver or spleen disease without substantial marrow involvement.

A normal aspirate from one site cannot exclude extramedullary plasma cell cancer. This is one of the most important feline differences.

6. Abdominal Ultrasound and Organ Sampling

Abdominal ultrasound evaluates:

• Liver

• Spleen

• Kidneys

• Abdominal lymph nodes

• Gastrointestinal tract

• Abdominal fluid

• Other masses

Possible findings include enlargement, nodules, altered echogenicity or a mottled appearance.

However, ultrasound appearance alone cannot diagnose plasma cell infiltration.

In the recent study, some cats had cytologically confirmed liver or spleen involvement despite having a normal or nonspecific ultrasound. Fine needle aspiration, biopsy or both may therefore be needed even when imaging changes appear mild.

This is a case where “the ultrasound looked normal” should not necessarily end the investigation.

7. Cytology, Histopathology and Immunophenotyping

Samples from the liver, spleen, lymph nodes, skin, bone or another mass may be examined by:

• Cytology

• Histopathology

• Immunohistochemistry

• Flow cytometry in selected cases

• Tests assessing immunoglobulin clonality

These tests help determine whether the cells are:

• Reactive plasma cells

• Neoplastic plasma cells

• Lymphoma cells with plasmacytic differentiation

• Another round-cell tumour

The distinction can be difficult, particularly when cells are poorly differentiated. Specialist pathology review may be useful before committing to long-term treatment.

8. Imaging for Bone Disease

Imaging may include:

• Skeletal radiographs

• Whole-body CT

• Targeted CT

• MRI

• Bone biopsy in selected cases

Myeloma-associated lesions may appear as:

• Discrete areas of bone loss

• Diffuse osteopenia

• Vertebral lesions

• Cortical destruction

• Pathological fracture

• Soft-tissue extension from bone

CT is more sensitive than conventional radiographs for many bone lesions. MRI is particularly useful when spinal cord compression or neurological disease is suspected.

A solitary vertebral plasmacytoma in one published feline case responded to melphalan and prednisolone, with complete MRI resolution documented two years later. This is encouraging, but it represents an individual case rather than a predictable outcome for every cat.

9. Eye, Blood Pressure and Cardiac Assessment

When hyperviscosity is suspected, the work-up may include:

• Retinal examination

• Blood pressure measurement

• Echocardiography

• Electrocardiography

• Chest imaging

• Serum or plasma viscosity measurement where available

A heart murmur in an older cat with high globulins should not automatically be assumed to be unrelated. Hyperviscosity can increase cardiac workload and contribute to heart failure in susceptible cats.

What Diagnostic Criteria Are Used?

Feline criteria are less firmly established than human criteria.

Commonly recommended evidence includes:

1. More than 10% bone marrow plasma cells, or more than 5% markedly atypical plasma cells

2. Serum paraproteinaemia

3. Osteolytic bone lesions

4. Immunoglobulin light-chain proteinuria

5. Confirmed visceral plasma cell infiltration

A diagnosis of a feline myeloma-related disorder is commonly supported when at least two of these criteria are present.

The exact label may still depend on where the cells are located. Marrow-dominant disease may be called multiple myeloma, while liver and spleen disease without substantial marrow involvement may be classified as multicentric extramedullary plasmacytoma.

What Else Can Look Like Myeloma?

Chronic Infection or Inflammation

Long-term infection and inflammatory disease commonly cause a broad polyclonal increase in globulins.

Examples include:

• Feline infectious peritonitis

• Chronic bacterial infection

• Fungal infection

• Severe dental or oral disease

• Chronic inflammatory intestinal disease

• Immune-mediated disease

Rarely, infection or inflammation can produce a narrow electrophoretic pattern that resembles a monoclonal gammopathy.

Lymphoma

B-cell lymphoma and lymphoplasmacytic lymphoma may produce an immunoglobulin and create a monoclonal gammopathy.

Tissue morphology, immunohistochemistry and the distribution of disease help distinguish lymphoma from a plasma cell neoplasm.

Reactive Plasmacytosis

Plasma cells may increase reactively in the bone marrow, spleen, liver or lymph nodes during immune stimulation.

A modest increase in normal-looking plasma cells does not automatically represent cancer. The degree of infiltration, cellular atypia, clonality, protein pattern and clinical findings must agree.

Monoclonal Gammopathy of Undetermined Significance

A monoclonal protein can occasionally be identified without evidence of organ damage or a demonstrable plasma cell tumour.

This has been reported rarely in cats. One cat in a retrospective multiple myeloma study had an M protein detected nine years before other evidence of myeloma-related disease was found.

Such cats require monitoring rather than automatically being treated with chemotherapy.

Other Causes of Bone Lesions

Osteolytic lesions may also be caused by:

• Lymphoma

• Osteosarcoma

• Metastatic cancer

• Bone infection

• Fungal disease

• Other primary bone tumours

Biopsy may be required when imaging and protein studies do not provide a secure diagnosis.

Plasma Cell Pododermatitis

Feline plasma cell pododermatitis is an inflammatory disorder affecting the paw pads.

It may cause soft, swollen, violaceous or ulcerated pads and prominent plasma cell infiltration on histopathology. Despite the name, it is not usually a malignant plasma cell tumour.

It must not be confused with a cutaneous plasmacytoma.

How Is Multiple Myeloma Treated in Cats?

Treatment depends on whether the disease is:

• Systemic

• Confined to one skin mass

• Confined to one bone

• Dominated by liver or spleen involvement

• Causing hyperviscosity

• Producing severe cytopenias

• Associated with kidney or neurological complications

There is no single protocol proven to be best for every cat.

Chemotherapy for Systemic Disease

Systemic myeloma-related disorders are usually treated with an alkylating chemotherapy drug combined with a corticosteroid.

Drugs reported in cats include:

• Cyclophosphamide

• Melphalan

• Chlorambucil

• Prednisolone or another corticosteroid

• Other rescue chemotherapy combinations

Historically, melphalan and prednisolone were commonly used. More recent feline data suggest that cyclophosphamide combined with a corticosteroid can produce similar response rates with less frequent bone marrow toxicity.

In a retrospective study of 50 cats, responses were common with both melphalan-based and cyclophosphamide-based treatment. Adverse effects were reported in 65% of melphalan-treated cats and 23% of cyclophosphamide-treated cats, with neutropenia being a major concern during continuous melphalan treatment. The study did not demonstrate a significant survival difference between the two drugs.

Does a high response rate mean the disease is cured?

No.

In the study, treatment response was largely measured by a reduction or normalisation of globulin levels.

A cat may achieve a major protein response while still harbouring neoplastic cells. Relapse and drug resistance remain possible.

The objectives of chemotherapy are usually to:

• Reduce the abnormal protein

• Improve appetite and activity

• Correct cytopenias

• Reduce organ infiltration

• Relieve pain

• Protect kidney function

• Improve quality of life

• Extend survival

What Are the Risks of Chemotherapy?

Potential adverse effects include:

• Neutropenia

• Anaemia

• Thrombocytopenia

• Increased infection risk

• Reduced appetite

• Nausea

• Vomiting

• Diarrhoea

• Lethargy

• Cumulative bone marrow suppression

Melphalan requires particularly careful CBC monitoring because delayed and potentially severe myelosuppression can occur.

Chemotherapy must be prescribed, dispensed and monitored by a veterinarian. Owners should also receive instructions for handling tablets and bodily waste safely.

Is Bortezomib Used in Cats?

Bortezomib is a proteasome inhibitor widely used for human multiple myeloma.

Its feline use remains investigational.

One published cat that had not achieved durable control with melphalan and prednisolone responded to bortezomib, with disappearance of the monoclonal gammopathy and recovery of blood-cell counts. Significant bone marrow toxicity occurred at the higher dose used in that case.

This single case is promising but does not establish bortezomib as routine first-line feline treatment. Access, cost, dose selection and toxicity monitoring currently limit its use.

How Are Cutaneous Plasmacytomas Treated?

A solitary skin plasmacytoma may be treated with complete surgical excision.

Before assuming that surgery alone is enough, the cat should be staged for systemic disease because feline plasma cell cancers frequently involve internal organs.

Staging may include:

• CBC and biochemistry

• Protein electrophoresis

• Urinalysis

• Abdominal ultrasound

• Liver and spleen sampling where appropriate

• Bone marrow assessment

• Imaging for bone lesions

Older feline case series suggest that cats with apparently isolated skin masses can experience prolonged survival after complete excision. However, multiple skin lesions, paraproteinaemia or internal organ involvement indicate a more systemic disorder that may require chemotherapy.

How Are Non-Cutaneous Extramedullary Plasmacytomas Treated?

Treatment depends on whether the tumour is solitary or multicentric.

A single accessible lesion affecting the intestine, oral cavity, eye or another site may be treated with:

• Surgery

• Radiation therapy

• Chemotherapy

• A combination of treatments

Multicentric disease involving the liver, spleen or several organs is generally managed as a systemic myeloma-related disorder.

Removing one enlarged spleen does not necessarily treat neoplastic cells elsewhere in the body, which is why complete staging remains important.

How Is a Solitary Bone Plasmacytoma Treated?

Possible treatments include:

• Radiation therapy

• Chemotherapy

• Surgery when instability, fracture or spinal compression is present

• Pain relief

• Bone-supportive medication in selected cases

Radiation is often considered for local control of a painful bone lesion, although feline evidence is limited.

Chemotherapy may be recommended because a solitary lesion can later progress to additional bone, skin or systemic plasma cell disease. One cat with a vertebral lesion experienced a prolonged response to melphalan and prednisolone, but later developed cutaneous plasmacytomas.

How Is Hyperviscosity Treated?

A cat with neurological, ocular, cardiovascular or bleeding complications may require emergency hospitalisation.

Treatment can include:

• Carefully planned intravenous fluids

• Oxygen

• Management of heart failure

• Blood pressure support

• Treatment of seizures

• Transfusion when severe anaemia is present

• Rapid initiation of treatment against the underlying cancer

• Therapeutic plasma exchange where available

Plasma exchange physically removes paraprotein-containing plasma and can reduce viscosity more quickly than chemotherapy alone.

It is a temporary bridge rather than a cure. The neoplastic cells will continue producing paraprotein unless the underlying cancer is controlled.

Small feline case series have reported improvement in congestive heart failure and other hyperviscosity-associated signs following plasmapheresis.

What Supportive Treatment May Be Needed?

Supportive treatment is selected according to the cat’s complications.

It may include:

• Intravenous or subcutaneous fluids

• Anti-nausea medication

• Appetite support

• Nutritional support

• Pain relief

• Blood transfusion

• Antibiotics for documented or strongly suspected infection

• Kidney support

• Management of hypercalcaemia

• Treatment of heart failure

• Radiation for painful focal lesions

• Treatment of pathological fractures

• Physiotherapy or mobility support

• Palliative and end-of-life care

Fluids must be individualised. A dehydrated cat with hyperviscosity may benefit from fluid therapy, but a cat with cardiac compromise or severe renal dysfunction can deteriorate if fluids are administered too aggressively.

Can Steroids Alone Treat Myeloma?

Corticosteroids may reduce some neoplastic plasma cells and temporarily improve appetite or inflammation.

However, corticosteroids alone produced a substantially lower response rate than alkylating chemotherapy combinations in the recent feline cohort.

Steroids may be selected when:

• Chemotherapy is declined

• The cat is too unwell for a full protocol

• The aim is strictly palliative

• Another medical issue changes treatment options

Starting corticosteroids before obtaining diagnostic samples can make lymphoma and other round-cell tumours more difficult to classify. When the cat is stable enough, important tissue samples should ideally be collected first.

How Is Treatment Monitored?

Monitoring may include:

• Physical examination

• Body weight

• Appetite and activity

• Complete blood count

• Kidney and liver values

• Calcium

• Total protein and globulin

• Serum protein electrophoresis

• Urinalysis

• Urine protein-to-creatinine ratio

• Repeat organ cytology or imaging

• Repeat bone imaging

• Eye examination

• Blood pressure

• Assessment for treatment toxicity

In the recent study, cats were commonly reassessed every 10 to 15 days during the first month and then at least monthly until a response, progression or chemotherapy toxicity was identified. Individual monitoring schedules should be adapted to the drug and patient.

What should owners monitor at home?

Record:

• Daily food intake

• Water consumption

• Urination

• Vomiting

• Stool quality

• Activity

• Body weight

• Ability to walk and jump

• Signs of pain

• Bruising or bleeding

• Gum colour

• Breathing

• Vision and pupil size

• Medication administration

A falling globulin result is encouraging, but treatment is not successful if the cat remains anorexic, weak, painful or clinically deteriorating.

What Is the Prognosis?

The prognosis depends heavily on the form of disease.

A completely excised solitary skin plasmacytoma may have a much better outlook than a systemic disorder causing severe anaemia, thrombocytopenia, hyperviscosity and kidney injury.

Prognosis for systemic myeloma-related disorders

The latest multicentre study reported:

• An overall median survival of 122 days

• A median survival of 315 days among cats initially treated with melphalan or cyclophosphamide combined with corticosteroids

• Individual survival ranging from no survival after diagnosis to more than 1,400 days

Anaemia and thrombocytopenia at diagnosis were independently associated with shorter survival.

These statistics are substantially more guarded than the commonly repeated claim that affected cats routinely survive for approximately 12 months.

They should not be treated as a countdown for an individual cat. The study included cats with widely different stages, treatments and complications, and many were lost to follow-up.

Factors that may support a better outcome include:

• Localised rather than systemic disease

• Complete excision of a solitary mass

• Absence of severe cytopenias

• Preserved kidney function

• No hyperviscosity syndrome

• No pathological fracture

• Good appetite and body condition

• A strong response to initial treatment

• Ability to continue treatment without major toxicity

Factors associated with a more guarded outlook include:

• Anaemia

• Thrombocytopenia

• Severe bone marrow replacement

• Kidney dysfunction

• Marked hypoalbuminaemia

• Hyperviscosity syndrome

• Significant neurological or cardiac complications

• Pathological fracture

• Progressive disease despite chemotherapy

• Severe appetite loss and weight loss

• Inability to tolerate treatment

When Is Myeloma an Emergency?

Seek immediate veterinary care if your cat develops:

• Sudden blindness

• Very large pupils

• Bumping into objects

• Retinal bleeding

• Seizures

• Head tilt or abnormal eye movements

• Severe disorientation

• Collapse

• Inability to stand

• Rapid or laboured breathing

• Open-mouth breathing

• Blue, grey or extremely pale gums

• Continuous or heavy bleeding

• Black, tar-like stool

• Vomiting blood

• Sudden severe lameness

• Suspected fracture

• Severe spinal pain

• Sudden paralysis

• Complete refusal of food with marked lethargy

• Rapid deterioration over several hours

These signs may indicate hyperviscosity, profound anaemia, severe thrombocytopenia, heart failure, spinal compression, pathological fracture, kidney failure or another life-threatening complication.

Do not wait for a routine oncology appointment when vision, breathing, neurological function or bleeding is unstable.

What Should You Do Next?

1. Obtain the complete laboratory results

Ask for copies of:

• CBC

• Blood smear interpretation

• Biochemistry

• Globulin and albumin

• Calcium

• Kidney values

• Urinalysis

• Urine protein-to-creatinine ratio

Look at trends rather than one result in isolation.

2. Ask whether protein electrophoresis has been performed

A high globulin result alone does not distinguish inflammation from a paraprotein-producing cancer.

Ask whether the laboratory identified:

• A monoclonal peak

• A biclonal peak

• A polyclonal pattern

• The size of the M protein

• A heavy or light-chain type

3. Determine where the neoplastic cells are located

Discuss whether your cat needs:

• Bone marrow sampling

• Liver aspiration

• Spleen aspiration

• Lymph node sampling

• Biopsy of a skin or other mass

• Imaging of painful bones

• Whole-body CT

• MRI for neurological signs

4. Assess for hyperviscosity

Ask whether your cat needs:

• Retinal examination

• Blood pressure measurement

• Cardiac assessment

• Blood-viscosity testing

• Emergency plasma exchange referral

5. Request oncology or internal medicine referral

Referral is particularly valuable when:

• The diagnosis remains uncertain

• Serum electrophoresis is abnormal

• Bone marrow or organs contain atypical plasma cells

• Hyperviscosity is suspected

• Chemotherapy is being considered

• A solitary bone lesion may benefit from radiation

• A major surgical decision is required

Referral does not commit you to aggressive treatment. It provides a clearer understanding of the realistic options.

6. Decide on the treatment goal

Ask whether the intended plan is to:

• Achieve remission

• Reduce the paraprotein

• Control one local tumour

• Relieve pain

• Restore appetite

• Stabilise the kidneys

• Treat hyperviscosity

• Provide comfort-focused care

7. Create an emergency plan

Know:

• Which signs require an immediate visit

• Where the nearest emergency hospital is

• Whether a blood transfusion is available

• Whether plasma exchange is available

• What to do if your cat stops eating

• What to do after vomiting chemotherapy

• Who to contact after hours

Common Mistakes Owners and Veterinary Teams Should Avoid

Assuming every high globulin result means myeloma

Inflammation, infection and lymphoma are more common explanations. Protein electrophoresis and tissue sampling are needed.

Assuming a monoclonal peak proves multiple myeloma

Monoclonal gammopathy can also occur with lymphoma, rare infections or an apparently benign gammopathy.

Stopping after a normal bone marrow sample

Feline plasma cell disease often involves the liver and spleen without marked marrow infiltration.

Relying on ultrasound appearance alone

A normal-looking spleen or liver can still contain neoplastic plasma cells.

Treating a skin plasmacytoma as harmless without staging

Some lesions are localised, but cats can develop multicentric or systemic plasma cell disease.

Assuming bone lesions must be present

Most cats in the recent systemic cohort did not have identified osteolytic lesions.

Measuring only total protein during treatment

The individual M protein is a more specific marker when electrophoretic measurement is available.

Increasing chemotherapy despite falling blood-cell counts

Treatment-associated myelosuppression can become severe, particularly with melphalan.

Ignoring vision or neurological changes

These can indicate hyperviscosity and require urgent treatment.

Treating published median survival as an expiry date

Individual outcomes vary from days to several years according to tumour type, disease burden and response.

Can Myeloma in Cats Be Prevented?

There is no proven method of preventing feline myeloma-related disorders.

Practical steps that may support earlier detection include:

• Routine blood testing in appropriate senior cats

• Investigating persistent hyperglobulinaemia

• Rechecking unexplained anaemia or thrombocytopenia

• Biopsying unusual skin masses

• Investigating persistent bone or spinal pain

• Recording body weight during senior visits

• Seeking assessment for recurring infections

• Investigating sudden vision changes immediately

• Following up abnormal protein electrophoresis results

Earlier diagnosis cannot guarantee a cure, but it may identify a localised tumour before systemic complications develop.

Frequently Asked Questions

Is multiple myeloma in cats curable?

Systemic multiple myeloma is rarely considered curable. Chemotherapy can produce remission and improve quality of life, but relapse is common. A completely removed solitary skin plasmacytoma or successfully controlled solitary bone lesion may have a much better outcome.

Can a cat have myeloma without bone lesions?

Yes. Cats commonly develop liver or spleen infiltration without obvious bone lesions or marked bone marrow involvement. The absence of bone destruction does not rule out a myeloma-related disorder.

Does a monoclonal gammopathy always mean cancer?

No. It strongly raises suspicion of a plasma cell or B-cell cancer, but rare inflammatory, infectious and apparently benign gammopathies occur. The result must be interpreted alongside tissue samples, imaging and evidence of organ damage.

Can a skin plasmacytoma spread?

Yes. Some cutaneous plasmacytomas remain localised and respond well to surgery, while others occur as part of multicentric disease or are followed by additional lesions. Complete staging is recommended before assuming that a skin mass is isolated.

How long can a cat live with multiple myeloma?

Survival varies from days to several years. A recent systemic feline study reported an overall median survival of 122 days and approximately 315 days among cats initially treated with melphalan or cyclophosphamide plus corticosteroids. Localised tumours may have a substantially better outlook.

Final Takeaway

Myeloma-related disorders are rare plasma cell cancers that can affect the bone marrow, liver, spleen, skin, bones and other tissues.

Cats do not always develop the classic bone marrow and bone-lesion pattern recognised in dogs and people. Extensive liver or spleen infiltration can occur even when bone marrow involvement is mild and the ultrasound changes are subtle.

The most important diagnostic steps are:

• Determine whether the elevated protein is monoclonal

• Identify where the abnormal plasma cells are located

• Assess the bone marrow and blood-cell counts

• Evaluate the liver and spleen

• Look for bone and kidney damage

• Check for hyperviscosity complications

Chemotherapy can produce meaningful responses, but systemic feline disease has a guarded prognosis. Solitary skin or bone tumours may behave very differently and can sometimes be controlled for much longer.

The immediate priorities are always the cat’s appetite, comfort, blood-cell counts, kidney function, vision, neurological status and ability to breathe normally. Sudden blindness, seizures, collapse, major bleeding or breathing difficulty should be treated as an emergency.

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If you are unsure what your cat’s globulin result, protein electrophoresis, bone marrow findings or plasma cell diagnosis means, ASK A VET™ can help you organise the results and understand what questions to discuss with your veterinarian next.