Cat Swollen Lymph Nodes: Causes & Treatment

Swollen lymph nodes in cats, medically termed lymphadenopathy, represent enlargement of the lymphoid tissue responsible for immune system function. Lymph nodes swell in response to infection, inflammation, immune system stimulation, or serious disease processes including cancer. Because lymph nodes are distributed throughout the body, swelling may be obvious (externally visible neck or jaw swelling) or hidden internally (only detectable via ultrasound or imaging). Lymphadenopathy is never normal and always warrants veterinary investigation, as swollen lymph nodes may indicate anything from a minor infection to life-threatening conditions such as lymphoma or feline leukaemia virus (FeLV) infection. Understanding what lymph nodes are and what they do, recognising symptoms of lymphadenopathy, understanding the full range of causes from benign to serious, knowing the diagnostic approach, understanding treatment options, and recognising when urgent care is needed, helps cat owners identify serious illness early and ensure appropriate veterinary management.

This comprehensive guide explores lymph node function, explains lymphadenopathy causes ranging from infections to cancer, details clinical presentation, discusses diagnostic procedures, presents treatment approaches, addresses prognosis for various causes, and provides guidance on when immediate veterinary care is essential.

Understanding Lymph Nodes in Cats

What Are Lymph Nodes?

Lymph nodes are small, bean-shaped organs throughout the body that produce and store lymphocytes (immune cells) and filter lymphatic fluid to trap pathogens and foreign substances.

Lymph Node Function:

• Immune cell production: Lymphocytes (white blood cells) produced and stored within lymph nodes; these cells fight infection
• Filtering function: Lymphatic fluid circulates through lymph nodes; pathogens, bacteria, cancer cells trapped and destroyed
• Immune response: When pathogens detected, lymph nodes enlarge as immune system mobilises and produces more lymphocytes
• Distributed location: Lymph nodes located throughout body: neck (cervical), jaw (mandibular), armpit (axillary), groin (inguinal), abdomen, chest

Normal vs Enlarged Lymph Nodes

• Normal size: Healthy lymph nodes small (5–10 mm); difficult to feel
• Enlarged: Swollen lymph nodes easily palpable; >10 mm; sometimes visible as lumps
• Lymphadenopathy definition: Abnormal enlargement of one or more lymph nodes; always abnormal and warrants investigation

Common Causes of Swollen Lymph Nodes

1. Infections (Most Common Benign Cause)

Bacterial Infections:

• Upper respiratory infection: Viral URI causes reactive lymph node enlargement in neck/jaw
• Dental disease: Mouth bacteria cause regional lymph node swelling
• Abscess: Localised infection causes swelling in draining lymph nodes
• Generalised infection: Systemic bacterial infection causes diffuse lymphadenopathy

Viral Infections:

• Feline leukaemia virus (FeLV): Causes lymphadenopathy; serious retroviral infection
• Feline immunodeficiency virus (FIV): Causes lymphadenopathy; progressive immunodeficiency
• Feline infectious peritonitis (FIP): Causes lymphadenopathy among other signs
• Upper respiratory viruses: Feline herpesvirus, calicivirus cause transient lymphadenopathy

Fungal Infections:

• Cryptococcosis: Fungal infection causing lymph node enlargement
• Histoplasmosis: Fungal infection affecting lymph nodes

Parasitic Infections:

• Toxoplasmosis: Parasitic infection causing lymphadenopathy
• Bartonellosis: Cat scratch disease; causes regional lymphadenopathy

2. Lymphoma (Cancer of Lymphocytes) — Most Common Neoplasia

Lymphoma is the most common feline cancer and a major cause of lymphadenopathy in cats, particularly senior cats.

What Is Lymphoma?

• Definition: Malignancy of lymphocytes (white blood cells); cancer cells multiply uncontrollably in lymphoid tissue
• Incidence: One of most common feline cancers; accounts for 30% of feline cancers
• Age predilection: Most common in cats >7 years old; can occur in younger cats, especially with FeLV/FIV

Lymphoma Types by Location:

• Gastrointestinal (GI) lymphoma: Most common form (50-60% of lymphoma cases); affects intestines, stomach, oesophagus
• Lymph node (multicentric) lymphoma: Affects multiple lymph node sites throughout body; classically linked to FeLV, now less common
• Mediastinal lymphoma: Affects chest lymph nodes; historically linked to FeLV; less common today
• Other sites: Kidneys, spine, skin, nasal cavity, liver, spleen (less common)

Risk Factors for Lymphoma:

• Feline leukaemia virus (FeLV): Most significant risk factor; FeLV-positive cats at dramatically increased lymphoma risk
• Feline immunodeficiency virus (FIV): Lesser risk factor than FeLV, but increases lymphoma risk
• Chronic inflammation: Ongoing inflammatory conditions increase risk
• Immunosuppression: Conditions weakening immune system increase risk
• Environmental toxins: Tobacco smoke exposure associated with increased lymphoma risk
• Age: Senior cats (>7 years) at higher risk

3. Other Cancers

• Carcinomas: Can metastasise to lymph nodes; cause secondary lymph node enlargement
• Melanoma: Can spread to lymph nodes
• Sarcomas: Soft tissue cancers can affect draining lymph nodes
• Mast cell tumours: Can metastasise to lymph nodes

4. Inflammatory Conditions

• Inflammatory bowel disease (IBD): Intestinal inflammation causes abdominal lymph node enlargement
• Chronic inflammation: Persistent inflammatory conditions cause reactive lymph node hyperplasia
• Autoimmune disease: Immune system attacking own tissues causes lymphadenopathy

5. Vaccination Reaction

• Recent vaccination: Lymph nodes draining vaccination site may swell temporarily (benign reactive hyperplasia)
• Timing: Swelling typically develops 1–4 weeks post-vaccination; resolves within 4–6 weeks
• Regional swelling: Typically only lymph nodes near vaccination site affected

6. Allergy or Hypersensitivity Reactions

• Environmental allergies: Uncommon in cats; can cause lymphadenopathy in some cases
• Food allergies: May contribute to lymphadenopathy in hypersensitive cats

Clinical Signs and Symptoms

Externally Visible Signs:

• Swelling in neck: Visible or palpable enlargement of cervical lymph nodes; lumpy neck
• Jaw swelling: Mandibular lymph node enlargement visible under jaw
• Swelling under front leg: Axillary lymph node enlargement visible/palpable
• Groin swelling: Inguinal lymph node enlargement palpable in groin area

General Illness Signs (Often Accompany Lymphadenopathy):

• Fever: Temperature >39.2°C (102.5°F); indicates infection or immune stimulation
• Lethargy: Lack of energy; reduced activity
• Appetite loss: Reduced interest in food; weight loss
• Weight loss: Progressive weight loss; particularly common with lymphoma or FeLV
• Vomiting: Particularly with GI lymphoma; also seen with other causes
• Diarrhoea: Associated with GI disease or intestinal lymphoma
• Poor coat quality: Dull, unkempt coat; dry skin

Symptoms Specific to Lymphoma:

• GI lymphoma: Weight loss (despite appetite sometimes normal), vomiting, diarrhoea, abdominal pain, palpable abdominal mass
• Multicentric lymphoma: Visible/palpable lymph node enlargement in neck, jaw, axilla, groin; systemic signs
• Mediastinal lymphoma: Breathing difficulty, cough, fluid in chest

Why Internal Lymphadenopathy May Not Show Obvious Symptoms:

• Not palpable: Internal lymph nodes (abdominal, chest, mediastinal) not accessible to physical examination
• Gradual onset: Disease develops insidiously; cats adjust to gradual changes
• Cats hide illness: Evolutionary survival strategy; cats mask symptoms until advanced disease

Diagnosis of Swollen Lymph Nodes

Physical Examination

• Lymph node palpation: Veterinarian carefully feels all accessible lymph nodes; assesses size, consistency, mobility
• Whole body examination: Assesses overall health, notes fever, weight loss, other physical findings
• Regional assessment: Notes any infection or inflammation draining to specific lymph nodes

Fine Needle Aspiration (FNA)

Fine needle aspiration is the quickest, simplest, least invasive diagnostic test for evaluating lymph node enlargement.

• Procedure: Small needle inserted into enlarged lymph node; cells drawn into syringe; spread on microscope slide; examined under microscope
• Painless: Minimally invasive; no sedation required; quick procedure
• Cell analysis: Cytology (cell appearance) assessed; can identify lymphoma, infection, inflammation
• Limitations: Cannot definitively diagnose in all cases; tissue biopsy sometimes required for definitive diagnosis

Tissue Biopsy

• Definitive diagnosis: Only way to definitively diagnose certain conditions, especially lymphoma
• Procedure: Small piece of lymph node tissue removed; examined microscopically (histopathology)
• More invasive: Requires sedation or anaesthesia; greater discomfort than FNA
• Accuracy: Histopathology more accurate than cytology for lymphoma diagnosis and subtype classification

Blood Tests

• Complete blood count (CBC): Assesses white blood cells; lymphoma may alter white cell patterns
• Chemistry panel: Evaluates organ function (kidney, liver); important for treatment planning
• FeLV/FIV testing: SNAP test or ELISA; critical because positive results significantly affect lymphoma prognosis and treatment decisions

Imaging

• X-rays (radiographs): Show lymph node size in chest; may reveal other abnormalities
• Ultrasound (abdominal): Excellent for visualising abdominal lymph nodes; can measure internal lymph nodes; assess organs
• CT scan: More detailed imaging; used for staging/extent assessment in cancer cases
• PET/CT scan: Advanced imaging showing areas of increased metabolic activity; helps identify cancer spread

Treatment of Lymphadenopathy

Treatment Depends on Underlying Cause:

Infections:

• Antibiotics: For bacterial infections; specific antibiotic chosen based on suspected/identified organism
• Antiviral treatment: Limited options for viral infections; primarily supportive care
• Antifungal medication: For fungal infections; long-term treatment often required
• Antiparasitic treatment: For parasitic infections

Lymphoma (Cancer):

• Chemotherapy: Modified CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) or other protocols
• Prednisolone (corticosteroid): Single-agent treatment; slower response but easier administration; common palliative approach
• Radiation therapy: For localised lymphomas in some cases
• Surgery: Rarely curative; sometimes used for specific situations (e.g., localised mediastinal lymphoma)
• Palliative care: Many owners choose supportive care (appetite stimulants, pain management) rather than aggressive chemotherapy

Inflammatory Conditions:

• Corticosteroids: Reduce inflammation; may shrink reactive lymph nodes
• Dietary management: Especially important for IBD; novel protein or limited-ingredient diet

Supportive Care:

• Pain management: Analgesia for comfort
• Appetite stimulation: Medications to encourage eating; important during cancer treatment
• Nutrition: High-quality diet; adequate protein important for cancer patients
• Monitoring: Regular check-ups to assess treatment response

Prognosis and Outcomes

Varies Dramatically by Cause:

• Infection-related: Excellent prognosis with appropriate treatment; often fully resolve
• Post-vaccination: Benign; resolves spontaneously within weeks
• Lymphoma: More guarded; depends on lymphoma type, stage, FeLV status, treatment chosen

Lymphoma Prognosis Details:

• GI lymphoma: With chemotherapy: median survival 1–2+ years; without treatment: 4–6 weeks
• Prednisolone monotherapy: Median survival 4–6 months; slower response than chemotherapy
• FeLV-positive: Significantly worse prognosis; shorter median survival than FeLV-negative cats
• High-grade lymphoma: Worse prognosis than low-grade; more aggressive disease
• Partial remission achievable: Some cats achieve temporary remission; relapses common
• Eventually fatal: Lymphoma in cats is sadly ultimately nearly always fatal despite treatment; goal is quality of life extension

Lymphadenopathy Related to FeLV and FIV

Feline Leukaemia Virus (FeLV):

• Retroviral infection: Serious virus suppressing immune system
• Lymphadenopathy common: Virus directly affects lymphoid tissue; lymph nodes enlarge
• Associated disease: FeLV dramatically increases lymphoma risk (primary risk factor); also causes anaemia, immunodeficiency
• Transmission: Saliva, blood, urine; spread through close contact
• Prognosis: No cure; management supportive; many cats die within 1–3 years of diagnosis

Feline Immunodeficiency Virus (FIV):

• Retroviral infection: Virus attacking immune system cells; progressive immunodeficiency
• Lymphadenopathy: Common in early/acute infection
• Secondary infections: Immunodeficiency makes cats susceptible to opportunistic infections
• Lymphoma risk: Increased risk but less dramatic than FeLV
• Prognosis: Some cats live years with FIV with supportive care; eventually opportunistic infections develop

When to Seek Veterinary Care

• Any visible/palpable lymph node swelling: Requires veterinary evaluation
• Fever + lethargy + appetite loss: Suggests infection or systemic illness
• Progressive weight loss: Especially in senior cats; could indicate lymphoma or other serious disease
• Persistent vomiting or diarrhoea: Could indicate GI lymphoma or other GI disease
• Breathing difficulty: Could indicate mediastinal lymphoma or other chest disease; emergency
• Senior cat with unexplained illness: Lymphoma screening appropriate; diagnostic workup warranted

This guide is based on research from PetMD, Cats.com, VCA Animal Hospitals, PDSA, Cornell University College of Veterinary Medicine, DVM360, and peer-reviewed case reports (PMC). Lymphoma accounts for 30% of feline cancers. GI lymphoma now most common (50-60% cases; historically less common than multicentric); shift likely due to FeLV vaccination/testing prevalence reducing FeLV-associated multicentric lymphoma. Historically (decades ago), mediastinal and multicentric lymphoma most common; directly linked to FeLV; mediastinal lymphoma now rare due to FeLV control. FeLV-positive cats at 60-fold increased lymphoma risk compared to FeLV-negative cats. FIV-positive cats at increased risk but less dramatic than FeLV. Lymphoma median survival without treatment 4–6 weeks; with prednisolone monotherapy 4–6 months (longer treatment time but slower response); with chemotherapy 1–2+ years possible. High-grade lymphoma more aggressive, shorter median survival than low-grade. Chemotherapy protocols: modified CHOP (cyclophosphamide, doxorubicin, vincristine, prednisolone); alternative protocols available. Chemotherapy response rates 50-90% with various protocols; toxicity moderate in most cats. Some cats achieve complete remission; relapses common. FNA accuracy ~80% for lymphoma diagnosis; cytology can identify lymphoma but tissue biopsy (histopathology) more accurate for subtype and grade. PET/CT detects metabolically active cancer cells; guides staging and treatment planning. Environmental tobacco smoke associated with increased lymphoma risk. Most common presenting signs: weight loss, vomiting, diarrhoea, anorexia (GI lymphoma); visible lymph node enlargement (multicentric); breathing difficulty (mediastinal). Fine needle aspiration safe, minimally invasive, can be done without sedation, useful screening test.