What are the common causes of enlarged lymph nodes?

Common causes of enlarged lymph nodes include local infection, skin wounds, and systemic inflammation, and they may also be linked to immune reactions or tumours. A vet will need to perform blood tests or a fine-needle aspirate to confirm the cause — consulting your vet is strongly recommended.

What initial steps can I take at home?

You can monitor temperature, appetite, and changes to the lump each day, photograph the area for reference, and avoid pressing on it. If symptoms worsen or persist, visit a vet as soon as possible.

What tests are typically run at the clinic?

Common tests include a complete blood count, blood biochemistry panel, X-ray or ultrasound, and fine-needle aspirate cytology. A tissue biopsy or further imaging may be arranged depending on the results.

Will enlarged lymph nodes cause my pet pain?

Swollen lymph nodes can sometimes be tender, especially when accompanied by inflammation or infection — your pet may flinch when touched or show a reduced appetite. If you suspect pain, bring your pet in for a vet check.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Lymphadenopathy & Lymphadenitis in Dogs & Cats: Symptoms, Diagnosis & Care [2025]

Enlarged lymph nodes can signal infection, immune response, or tumour — cytology or biopsy is needed to identify the cause and guide treatment.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: AVMA, WSAVA, National Taiwan University College of Veterinary Medicine

When to See a Vet

Seek immediate veterinary care (emergency)

•Persistent high fever lasting more than one day with no improvement
•Rapidly enlarging lump or skin breakdown with bleeding
•Rapid breathing or signs of severe lethargy and altered consciousness

Schedule a clinic visit soon (within 24–72 hours)

•A noticeable lump in the neck or armpit area that persists for two or more days
•Pet visibly flinches or trembles when the area is touched
•Significant decrease in energy or appetite, or unexplained weight loss

01What symptoms suggest something is wrong?

Enlarged lymph nodes are often accompanied by local discomfort or systemic signs — owners can monitor through touch and observation to assess whether a vet visit is needed.

Noticeable lumps felt at the neck, armpits, or groin
Pet flinches or shows pain when the lump is pressed
Persistent fever or abnormal body temperature requiring medical evaluation
Lethargy, reduced activity, or decreased appetite
Local skin redness, broken skin, or purulent discharge around the lump
If the lump persists or grows, seek veterinary attention promptly

Seek emergency care immediately if you notice the following symptoms:

⚠️ High fever lasting more than one day with no improvement
⚠️ Rapidly enlarging lump or skin breaking open and bleeding
⚠️ Laboured breathing or signs of severe lethargy or altered consciousness

02How to assess the situation at home — what to monitor and when to go to the emergency clinic

At-home monitoring should focus on tracking temperature, alertness, and changes to the lump — detailed records help the vet assess the situation quickly.

Take your pet's temperature at the same time each day and log the readings
Note any changes in alertness, activity level, and responsiveness
Record appetite, water intake, and elimination habits
Weigh your pet regularly to track any weight changes over time
Take close-up photos of the lump and video of any behavioural changes for comparison
If medications or supplements are being given, note the name and time of each dose

03How will the vet make a diagnosis? Common diagnostic procedures

The vet will combine clinical examination with laboratory or imaging findings to evaluate the likely cause and severity of the lymph node enlargement.

Full-body and localised palpation to evaluate lymph node size and tenderness

Complete blood count (CBC) to assess infection or inflammatory response

Blood biochemistry panel to evaluate liver, kidney, and overall organ function

X-ray or ultrasound to detect changes in thoracic or deep lymph nodes

Cytology or fine-needle aspirate (FNA) as an initial screen for neoplasia or infection

Tissue biopsy or specialist referral arranged if indicated

04How to treat and care for your pet after diagnosis — medications, diet, and care guide

Treatment and follow-up are determined by the test results — medication, surgery, or long-term monitoring may all be used, and home care and recheck visits are essential.

A medication or treatment plan tailored to the diagnostic findings and underlying cause
Scheduled follow-up visits to monitor lymph node size and clinical response
Supportive care at home: adequate rest and good nutrition
Avoid squeezing or irritating the affected area to minimise discomfort
Periodic blood work or imaging recommended to track disease progression
Complex cases may be referred to an oncology or internal medicine specialist

05What to prepare before the vet visit — key information to help the vet identify the cause quickly

Note when the problem started and describe the first symptoms you noticed in detail

List any daily changes in appetite, water consumption, and elimination

Prepare a log of body temperature, weight, and how symptoms have progressed

Bring a list of all current medications and supplements your pet is receiving

Take photos and videos of the lump to show the vet at the appointment

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.