A swollen lymph node is one of the most common findings families bring us, and it almost always raises the same first question: should I be worried? The answer is that an enlarged node is genuinely worth investigating, but most of the time the explanation turns out to be something manageable. A lymph node is essentially a checkpoint where immune cells gather to respond to threats, and it swells whenever that response ramps up, whether the trigger is a tick-borne infection, a chronically inflamed skin allergy, a bad tooth, an autoimmune process, or a cancer. The node itself does not announce which of these is happening. What it does is signal that the body is working on something, and our job is to figure out what.

At The Gentle Vet in West Caldwell, our diagnostic capabilities include in-house blood work, real-time abdominal and cardiac ultrasound, and ultrasound-guided biopsy when a tissue answer is needed. We focus on giving you a complete picture, with the reasoning behind every step explained as we go. If you have noticed a lump under the jaw, a swelling behind a knee, or any change that does not seem right, get in touch with us and we will work through it together.

What the Swelling Tells You

  • Immune activation is the common thread: the node enlarges because cells inside it are multiplying to address something.
  • Infection and inflammation outnumber cancer: the worst-case scenario is real but not the statistical default.
  • The pattern carries most of the diagnostic weight: location, count, firmness, and accompanying signs each shift the suspicion.
  • A short workup usually resolves the question: a fine-needle aspirate frequently delivers an answer the same day.

Why Does a Lymph Node Get Larger in the First Place?

Lymph nodes are filters scattered along the lymphatic system, and each one collects fluid draining from a specific area of the body. Pathogens, inflammatory debris, and abnormal cells flow through these stations, where resident immune cells inspect what arrives and mount a response when something needs addressing. When that response gets loud, the node fills with multiplying lymphocytes and other cells, expanding in size until you can feel it from the outside.

The accessible nodes families can feel from home cluster in five predictable areas, all described in detail in this guide to the lymph nodes you can check at home. Those locations are under the jaw, in front of the shoulders, in the armpits, in the groin, and behind the knees. We palpate all of these at every preventive visit, and our wellness and preventive care exams are where a subtle change is most often caught early, while it is still easy to investigate.

What Could the Swelling Be?

The list of possible causes sorts into a handful of broad categories, each with its own pattern of clues.

Cause category What the node is doing What you might also notice
Reactive to local infection Filtering a nearby threat Often tender, soft, near a wound or sore tooth
Systemic infection Responding throughout the body Several nodes enlarged, fever, lethargy
Cancer (especially lymphoma) Abnormal cells multiplying Firm, painless, multiple nodes, pet acts well
Immune-mediated disease Activating against the body’s own tissues Other systemic signs, anemia, skin disease
Chronic local irritation Draining ongoing inflammation One node near a chronic problem like skin allergy

Each row gives a starting point, not a verdict. The real diagnostic value comes from reading these clues alongside the exam and following them where they lead.

Is It an Infection?

Infections are responsible for the majority of enlarged lymph nodes we see, and they break down by category.

Tick-borne disease is a year-round concern in New Jersey:

  • Lyme disease: commonly enlarges nodes near the bite site, often paired with fever, joint pain, or lameness.
  • Ehrlichia and anaplasma: produce both reactive node enlargement and direct effects on platelets and white cell counts.

The strongest preventive lever here is consistent year-round protection, and our pharmacy carries flea and tick prevention for dogs and flea and tick prevention for cats to help prevent tick-borne diseases.

Other bacterial infections:

  • Leptospirosis: transmitted through wildlife urine and standing water, with systemic illness accompanying the node activation.
  • Mycobacteriosis: sometimes presents in cats as enlarged regional nodes with little else.

Fungal disease varies by region but matters for any pet who has traveled:

Cat-specific viruses:

Parasites:

Local causes deserve their own mention. A bad tooth, an infected wound, an ear infection, or a chronic skin problem can each enlarge whichever node drains that area, often without affecting any others. These are common, treatable, and resolve completely once the underlying cause is addressed.

Is It Lymphoma or Another Cancer?

This is the category families fear most, and it deserves a thorough explanation rather than a brief mention. Lymphoma is the most common cancer that presents with enlarged lymph nodes in dogs, and understanding what it actually looks like helps families distinguish concerning changes from routine ones.

Canine lymphoma is a cancer of the lymphocytes themselves, the immune cells that normally populate lymph nodes. When those cells turn cancerous, they multiply and accumulate in the nodes, producing the characteristic enlargement. Roughly 1 in 15 dogs and 1 in 8 Golden Retrievers will develop it during their lifetime, which makes it one of the most common cancers we see in companion animals.

What Lymphoma Looks Like

The classic presentation has features that distinguish it from infection-driven node enlargement:

  • Painlessness. Lymphoma nodes are firm and rubbery to the touch without bothering the pet at all, while infection-related nodes are usually tender.
  • Symmetry. Multiple nodes on both sides of the body enlarge at once, so matching swellings under both jaws or behind both knees are characteristic, in contrast to the single-sided pattern of local infection.
  • A normal-acting pet. The most paradoxical feature, and the one that causes the most missed diagnoses, is that affected dogs often act completely well in the early stages. They eat, play, and behave normally even as the nodes become strikingly large.
  • Steady growth. Nodes that grow noticeably over a week or two without explanation deserve evaluation rather than continued observation.
  • Speed of progression. Once symptoms do develop, lymphoma can progress quickly, which is why early diagnosis matters for treatment planning.

Subtypes and Why They Matter

Lymphoma is not a single disease. Several subtypes exist, and they respond very differently to treatment. The most common form in dogs is multicentric lymphoma, which affects peripheral nodes and is what most families encounter. Other forms include alimentary lymphoma (involving the gastrointestinal tract), mediastinal lymphoma (affecting nodes in the chest), and cutaneous lymphoma (affecting the skin). Within these anatomical categories, the cancer is further classified by the type of lymphocyte involved, with B-cell lymphomas generally responding better to chemotherapy than T-cell lymphomas, and high-grade tumors progressing faster than low-grade tumors but often responding more dramatically to treatment.

This is why lymphoma diagnosis and subtype shapes treatment in meaningful ways. A fine-needle aspirate is usually the first diagnostic step and can often confirm lymphoma, but flow cytometry or immunohistochemistry is needed to determine the specific subtype, which guides treatment decisions and the realistic expectations we set with families.

Treatment and What to Expect

When lymphoma is diagnosed, treatment options range from observation with palliative care to multi-agent chemotherapy protocols. Chemotherapy in dogs differs substantially from chemotherapy in humans: doses are calibrated to maintain quality of life, side effects are usually mild, and most dogs continue normal activities throughout treatment. The realistic goal is remission and an extended period of good quality time, not a cure. With the most common chemotherapy protocols, the majority of dogs with multicentric B-cell lymphoma reach remission, and many enjoy a year or more of normal life after diagnosis. Some live considerably longer.

Other Cancers That Affect Nodes

Lymphoma is not the only cancer that enlarges lymph nodes. Other tumors, including mast cell tumors, melanoma, and various carcinomas, can spread to regional lymph nodes from a primary site elsewhere in the body. A firm, fixed lymph node near a known skin mass or tumor warrants prompt testing for this reason, since detecting metastasis early changes treatment planning significantly.

Screening for At-Risk Breeds

The good news is that the diagnostic landscape continues to improve. Blood-based screening tests can now detect lymphoma months before visible lymph node enlargement, which is particularly relevant for breeds at higher risk. Golden Retrievers, Boxers, Bullmastiffs, Bernese Mountain Dogs, Rottweilers, and Scottish Terriers all show meaningfully elevated rates of lymphoma compared to the general population. For middle-aged and senior dogs in these breeds, adding lymphoma screening to annual bloodwork is increasingly common and catches the disease at a more treatable stage.

Feline lymphoma follows different patterns. In cats, the disease more commonly affects the gastrointestinal tract than the peripheral nodes, and the presentation, treatment, and prognosis differ from canine lymphoma in important ways.

Could It Be an Immune Problem or Allergy?

A smaller but real category of causes is neither infectious nor cancerous. Immune-mediated hemolytic anemia and related autoimmune conditions can activate lymph nodes as the body mounts an immune response against its own tissues. Chronic allergies, particularly when secondary skin infection has developed, keep the draining nodes activated through ongoing inflammation. A recent vaccine can produce mild, temporary enlargement of the closest node, which is an expected immune response, while vaccination reactions that persist or spread beyond the expected pattern deserve a closer look. None of these can be distinguished from infection or cancer by feel alone, so they warrant the same diagnostic approach.

How Does the Pattern Help Us Narrow It Down?

Before any test runs, the pattern of what you found does meaningful diagnostic work. A single soft, painful node next to an obvious local problem nearly always reflects reactive inflammation from that local cause. Several firm, painless nodes in a dog who otherwise seems completely healthy raises strong concern for lymphoma. Generalized enlargement accompanied by fever, lethargy, or other systemic signs points toward a body-wide infection or immune-mediated process. A node that has become fixed to the tissue beneath it is more concerning than one that slides freely under your fingers. None of this replaces testing, but it tells us where to begin and which test to run first.

How Do We Confirm What Is Going On?

Confirming the cause usually moves quickly. A fine needle aspiration is typically the first step: a small-gauge needle collects cells from the node for microscope evaluation, the procedure rarely requires sedation, and it often distinguishes among reactive inflammation, infection, and cancer in a single visit. When cytology results are inconclusive, or when confirming a lymphoma subtype is essential for treatment planning, a biopsy provides a larger tissue sample and more definitive answers. We can perform that procedure through our soft tissue surgery services. Complete bloodwork, tick-borne disease panels, and our in-house ultrasound, including ultrasound-guided sampling of deeper nodes, fill in the rest of the picture.

What Does Treatment Actually Involve?

Once we know what we are treating, the approach is matched to the diagnosis. Bacterial infections respond to targeted antibiotics, often guided by culture and sensitivity. Tick-borne disease typically requires a course of doxycycline. Fungal infections need extended antifungal therapy, sometimes for months. Immune-mediated disease calls for immunosuppression. Lymphoma is treated with chemotherapy protocols designed to reach remission while preserving quality of life, and we coordinate with specialty oncology for these cases.

One common and entirely fixable cause deserves direct mention: chronic dental disease maintains constant activation in the jaw nodes, and our dental care services address that at the source. Starting treatment before the cause is confirmed almost always delays the right answer.

A macro, close-up shot focusing on the muzzle of a fluffy white dog lying down on its side, with its mouth slightly open revealing its pink tongue and teeth.

When Does the Swelling Mean Act Now?

Several patterns of swelling warrant a same-day call: multiple nodes that have enlarged suddenly, swelling that interferes with breathing or swallowing, or any node finding combined with lethargy, fever, or lack of appetite in your pet. A single firm, painless lump without accompanying signs should be evaluated within a day or two. A stable, mildly enlarged node noticed on a routine home check, in a pet who seems otherwise well, can usually be evaluated within the week. When the urgency is unclear, call us and describe what you are finding, and our sick visits handle same-day evaluation when it is appropriate.

Frequently Asked Questions About Enlarged Lymph Nodes

My Dog Has a Lump Under His Jaw. Does It Mean Cancer?

Not necessarily. A lump in that location could be an enlarged submandibular lymph node, a salivary gland issue, a fatty lipoma, an abscess, or several other possibilities. A fingertip exam, followed in most cases by a fine-needle aspirate, sorts these out quickly. Bring it in for evaluation rather than assuming the worst.

Does the Number of Swollen Nodes Change What It Might Be?

Yes, significantly. A single enlarged node usually points to a local problem draining into that specific filtering station, while multiple enlarged nodes simultaneously raise concern for a systemic process such as a body-wide infection, immune-mediated disease, or lymphoma. This is precisely why we examine all the accessible nodes at every visit, not only the one you noticed at home.

Can a Swollen Node Sometimes Be Nothing Serious?

Yes, frequently. Many enlarged nodes are reactive to a minor and self-limiting cause, and they shrink back to normal once that cause resolves. The challenge is that a reactive node and a more serious one can feel identical to your fingertips, so confirming that a node truly represents nothing serious requires actual evaluation rather than wishful observation.

Does the Speed of Growth Help Identify the Cause?

The pace of change is a useful clue. A node that swells rapidly over a day or two alongside an obvious wound or illness usually reflects active infection. One that enlarges suddenly in a dog who otherwise feels fine raises more concern for lymphoma. A node that has gradually crept upward over months might fit a chronic infection or an indolent process. The growth rate does not provide a diagnosis on its own, but it helps direct the workup.

Can a Node Stay Enlarged Long-Term Without It Being Serious?

It can. Some nodes remain mildly enlarged after a resolved infection or alongside a chronic but benign condition like a skin allergy, without anything concerning underlying them. The key is whether the node is stable or changing over time. A node that holds steady at a small size is generally reassuring; one that continues to grow, becomes firmer, or fixes to the surrounding tissue needs reevaluation.

From Finding the Lump to Getting a Clear Answer

The hardest part of finding a swollen node is the uncertainty of not knowing what it represents, and a structured workup, reading the pattern first and then confirming with a quick test, resolves that uncertainty quickly. Most enlarged nodes turn out to be reactive and resolve as the cause is treated, and even the more serious diagnoses come with more treatment options when they are caught early.

If you have found something on your pet, contact us and our team will work through it with you.