Swollen Lymph Nodes in Cats: Causes and Treatment

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-02

Swollen lymph nodes in cats are enlarged immune system structures that usually react to infection or inflammation somewhere in the body, though cancer such as lymphoma is also a possibility. You can often feel these nodes under the jaw, in front of the shoulders, and behind the knees. A veterinarian can usually tell a lot from where the swelling is and how the nodes feel.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

• Lymph nodes are normal immune organs, and they enlarge when immune cells multiply to fight something [1].
• The nodes you can most easily feel on a cat are under the jaw, in front of the shoulder blades, and behind the back legs (the popliteal nodes).
• Reactive swelling from infection or inflammation is common, but lymphoma is a real concern in middle-aged to older cats [2].
• Fine needle aspiration is usually the next step because it is quick, minimally invasive, and often gives a diagnosis without surgery.
• Swelling with lethargy, not eating, trouble breathing, or a node that keeps growing needs prompt veterinary care.

What Swollen Lymph Nodes in Cats Look Like

Lymph nodes are small, bean-shaped organs packed with white blood cells. They act as filters and meeting points where immune cells trap germs and mount a response [1]. That design explains why they swell. When the immune system ramps up, lymphocytes multiply quickly, and the node gets bigger [2].

Normal lymph nodes are small and soft. In a healthy cat, you usually cannot see them, and many are hard to feel through fur and fat. When a node is enlarged, it may feel like a firm pea, a grape, or even a plum. Some enlarged nodes are movable and slightly tender. Others feel fixed in place and rock hard.

Swollen Lymph Nodes in Cats Neck and Under Jaw

The mandibular nodes sit under the jaw and drain the head, mouth, and throat. Owners often notice these first because they are easy to see and feel. A cat with swelling here may have a lump under the chin, drool, have bad breath, or resist having the mouth touched. Dental disease, oral wounds, and infections of the mouth or throat commonly cause this pattern.

Swelling in the neck area can also involve the prescapular nodes, which sit just in front of the shoulder blades. A study of one cat with enlarged mandibular and prescapular nodes found pyogranulomatous inflammation caused by a Neisseria species, and the cat recovered after a four-week course of amoxicillin-clavulanate at 20 mg/kg by mouth every 12 hours [3]. That case shows how a bacterial infection can mimic more serious disease.

Swollen Lymph Nodes in Cats Under Jaw and Throat

Swollen lymph nodes in cats throat and under the jaw often go together. The throat region contains nodes that drain the mouth, tonsils, and upper airway. Causes range from dental abscesses to viral infections to cancer. Cat scratch disease, caused by Bartonella henselae, is a well-known cause of lymph node swelling in the nodes that drain a scratch or bite site, and it can look like a problem with the salivary glands or throat [4].

Swollen Lymph Nodes in Cats Back Legs

The popliteal lymph nodes sit behind the knee on the back of each hind leg. They drain the lower leg, paw, and skin of that limb. Swelling here often points to a wound, bite, or skin infection on that leg. Because these nodes are tucked behind the knee, owners sometimes mistake them for a growth or a knee problem. Your veterinarian can compare the left and right sides during an exam.

Main Causes of Swollen Lymph Nodes in Cats

Lymph nodes enlarge for two broad reasons. Reactive enlargement means the node is doing its job and responding to something nearby. Neoplastic enlargement means cancer cells, usually lymphoma, are growing inside the node itself [2].

Reactive nodes tend to be soft, movable, and sometimes painful. They often shrink once the underlying problem is treated. Cancerous nodes tend to be firm, rubbery, or fixed, and they keep growing. The only way to know for sure is to sample the node.

Lymphoma is the most common cancer concern when nodes stay enlarged. It occurs in middle-aged to older cats, and no breed is known to be at higher risk [2]. Infection with feline leukemia virus or feline immunodeficiency virus raises the risk [2]. Because lymphocytes live in every organ, lymphoma can start in the lymph nodes, chest, digestive tract, kidneys, nervous system, eyes, skin, nose, or blood [2].

In a review of 72 cats with neutrophilic or pyogranulomatous lymphadenitis, feline infectious peritonitis was the most common cause at 35 percent, and cancer was the next most common at 15 percent [5]. Nine cats, about 12.5 percent, had steroid-responsive lymphadenitis, meaning their nodes improved with anti-inflammatory or immunosuppressive treatment and no infection or tumor was found [5].

Fungal disease is uncommon but can look exactly like lymphoma. One immunocompetent cat with seizures and enlarged lymph nodes turned out to have mucormycosis, a fungal infection that caused generalized lymphadenopathy and lung masses [6]. Another Persian cat had systemic cryptococcosis with skin nodules and generalized lymph node swelling but no typical respiratory or neurologic signs, which made it easy to mistake for lymphoma [7]. These cases are why sampling matters.

Red Flags That Make It an Emergency

Some signs mean you should not wait for a routine appointment. Go to an emergency clinic now if your cat:

• Breathes with an open mouth, makes noise when breathing, or has blue gums
• Collapses, cannot stand, or seems barely responsive
• Has a rapidly growing lump that appeared over hours to a day
• Has a fever with severe weakness or vomiting
• Has a swollen belly along with the node swelling, which can point to fluid buildup or an abdominal mass

A swollen belly with lymph node changes deserves a close look. You can read more about possible causes in Cat Swollen Belly Causes and Why Is My Cat's Belly Swollen?.

Swelling around the head and ears can also have other explanations. If your cat has ear pain, discharge, or a fluid-filled pocket on the ear flap, see Cat Ear Infection with Swelling: What to Do and When to Worry and Cat Ear Hematoma: Causes and Treatment.

What You Can Safely Do at Home While Waiting

You cannot treat swollen lymph nodes at home, but you can keep your cat comfortable and give your veterinarian better information.

• Do not squeeze, poke, or massage the swollen node. You could cause pain or spread infection.
• Take photos of the lump from a few angles and note the date you first saw it. Measure it against a coin if you can.
• Write down any other signs, such as appetite changes, vomiting, diarrhea, sneezing, limping, or hiding.
• Check for wounds, scabs, or bite marks, especially on the legs, head, and tail base. Cat scratches and bites are common sources of infection [4].
• Keep your cat indoors and away from other cats until you know what is going on.
• Offer soft, smelly food if eating seems painful. Warm it slightly and avoid hard kibble if the mouth or jaw is sore.
• Do not give any human pain reliever. Many are toxic to cats, and the dose must be calculated by a veterinarian based on your cat's weight and health.

If your cat stops eating for more than 24 hours, seems painful when swallowing, or has trouble breathing, call your veterinarian right away instead of waiting.

What Your Veterinarian Will Check and Test

Your veterinarian will start with a full physical exam. They will feel all the accessible lymph nodes, including the ones under the jaw, in front of the shoulders, in the armpits, in the groin, and behind the knees. They will also check the mouth, eyes, skin, abdomen, and breathing.

Fine Needle Aspiration

Fine needle aspiration is usually the next step. Your veterinarian inserts a thin needle into the enlarged node, pulls out a small sample of cells, and looks at them under a microscope. This takes only a minute or two and rarely needs sedation. It can often distinguish reactive hyperplasia from lymphoma, and it can reveal infections such as fungal organisms or pyogranulomatous inflammation [5][6][3].

If aspiration does not give a clear answer, the next step may be a biopsy, which removes a piece of the node for a pathologist to examine [2].

Other Tests

Your veterinarian may also recommend:

• Blood work, including a complete blood count and chemistry panel, to look for anemia, organ changes, or high eosinophil counts [9]
• FeLV and FIV testing, because both viruses raise lymphoma risk [2]
• Imaging such as X-rays or ultrasound to look for enlarged internal lymph nodes or masses in the chest or abdomen [9][6]
• Infectious disease testing for feline coronavirus, Bartonella, mycobacteria, or fungal organisms when the pattern fits [5][4][7]
• Cultures from a node or wound if a bacterial or fungal infection is suspected [6][3]

Treatment depends entirely on the cause. Bacterial infections are treated with antibiotics chosen for the specific organism, and one reported cat recovered fully after four weeks of amoxicillin-clavulanate at 20 mg/kg by mouth every 12 hours [3]. Your veterinarian will calculate the right drug and dose for your cat.

Lymphoma is often treated with chemotherapy using several drugs [2]. Side effects can include vomiting, diarrhea, lack of appetite, and fever, but cats do not lose their hair from chemotherapy [2]. Steroid-responsive lymphadenitis is treated with anti-inflammatory or immunosuppressive drugs [5]. Fungal infections need specific antifungal therapy, and the outcome varies with the organism and how far it has spread [6][7].

Prevention and Monitoring

You cannot prevent every cause of lymph node swelling, but you can lower some risks.

• Keep your cat indoors to reduce fights, bites, and exposure to FeLV and FIV [2].
• Test new cats for FeLV and FIV before introducing them to your household [2].
• Keep up with dental care, since mouth infections can enlarge the nodes under the jaw.
• Treat wounds promptly. Clean minor scratches and call your veterinarian if the area swells.
• Do a monthly home check. Run your hands gently along the jaw, shoulders, and behind the knees so you learn what normal feels like for your cat.
• If a node was sampled and diagnosed, follow the recheck schedule. Nodes that shrink and then enlarge again need another look.

If you have a middle-aged or older cat, pay attention to subtle changes. Weight loss, vomiting, diarrhea, appetite loss, lethargy, increased thirst or urination, or breathing changes can all accompany lymphoma depending on where it grows [2]. A cat with frequent vomiting and an enlarged mesenteric lymph node may have alimentary lymphoma, which is the most common neoplastic subtype in cats [9].

Limitations and When to Contact a Veterinarian

This article gives general information, but every cat is different. Only a veterinarian who examines your cat can diagnose the cause of swollen lymph nodes and choose the right treatment.

Call your veterinarian the same day if your cat has a new swollen node, a fever, is eating less, is hiding more, or has a wound that looks infected.

Go to an emergency clinic now if your cat has trouble breathing, open-mouth breathing, collapse, severe weakness, a rapidly growing mass, or a swollen belly with vomiting or pain.

Schedule a routine visit if you found a small, stable lump and your cat is otherwise acting normal. Even then, do not wait weeks to see if it changes. Early sampling is simple and gives you answers.

Frequently Asked Questions

Are swollen lymph nodes in cats always cancer?

No. Most enlarged lymph nodes in cats are reactive, meaning they are responding to an infection or inflammation nearby. In one review, feline infectious peritonitis was the most common cause of lymphadenitis, and cancer was second. Fine needle aspiration is how your veterinarian sorts this out.

Can I feel my cat's lymph nodes at home?

Yes, some of them. The easiest to find are the mandibular nodes under the jaw, the prescapular nodes in front of the shoulders, and the popliteal nodes behind the knees. They should feel small and soft. If one feels like a firm pea or larger, have your veterinarian check it.

How long does it take to get aspiration results?

Cell samples from a fine needle aspiration are often reviewed in the clinic the same day. If the sample goes to an outside laboratory, results usually come back within a few days. A biopsy for tissue examination can take longer.

Will antibiotics make the swelling go away?

Only if a bacterial infection is the cause. Antibiotics will not shrink a node enlarged by lymphoma, a virus, or a fungal infection. Giving antibiotics without a diagnosis can delay the right treatment, so sampling first matters.

Should I wait and see if the swelling goes down on its own?

A small node that shrinks within a few days while your cat acts normal may be fine to monitor. A node that stays enlarged, keeps growing, feels hard, or comes with any other sign needs a veterinary visit. Waiting too long can let a treatable problem get worse.

Related Articles

• Cat Swollen Belly Causes
• Why Is My Cat's Belly Swollen?
• Cat Ear Infection with Swelling: What to Do and When to Worry
• Cat Ear Hematoma: Causes and Treatment
• Cat Ear Infection with Hair Loss: Causes and Treatment
• Cat Skin Rash with Swelling: When to Worry

References

1. The Immune System of Cats - Cat Owners. Merck Veterinary Manual.
2. Immune System Tumors in Cats - Cat Owners. Merck Veterinary Manual.
3. Pyogranulomatous lymphadenitis with Splendore-Hoeppli phenomenon caused by Neisseria species in a domestic shorthair cat. Journal of veterinary internal medicine, 2026.
4. Cat Scratch Disease - The Inconspicuous Cause of Cervical Lymphadenopathy. Journal of pharmacy & bioallied sciences, 2025.
5. Diagnosis of pyogranulomatous and neutrophilic lymphadenitis in 72 cats presenting to a referral hospital: with a focus on nine cats with steroid-responsive lymphadenitis. Journal of feline medicine and surgery, 2026.
6. Ultrasonographic and Radiographic Features of Mucormycosis Causing Generalized Lymphadenopathy and Cranioventral Pulmonary Masses in an Immunocompetent Cat. Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association, 2026.
7. Rare Case of Systemic Cryptococcal Lymphadenopathy in a Persian Cat. Veterinary medicine and science, 2025.
8. Immune System Responses in Cats - Cat Owners. Merck Veterinary Manual.
9. Feline paraneoplastic hypereosinophilic syndrome associated with lymphocytic intestinal lymphoma. Brazilian journal of veterinary medicine, 2026.

Further Reading

• Merck Veterinary Manual: Cat Owners
• Cornell Feline Health Center: Health Information
• American Veterinary Medical Association: Pet Care