Dog Swollen Lymph Nodes - Causes, Diagnosis & When to See a Vet

> Disclaimer: This article is for informational purposes only and is not intended to replace professional veterinary advice. If your dog has swollen lymph nodes or any health concerns, please consult your veterinarian for diagnosis and treatment.

Quick Summary

Swollen lymph nodes in dogs indicate that the immune system is responding to infection, inflammation, or disease. Lymph nodes filter harmful substances and help fight illness, so enlargement often means the body is actively responding to a threat. While many causes are treatable—such as infections—swollen lymph nodes can sometimes indicate serious conditions like lymphoma. Any unexplained swelling warrants a veterinary exam.

What Does Swollen Lymph Nodes Look Like in Dogs?

Lymph nodes are small, bean-shaped glands that normally feel firm but subtle when gently palpated. In a healthy dog, you may barely notice them.

• Visible lumps under the jaw, in front of the shoulders, in the armpits, or behind the knees
• Firm, sometimes painful swellings that grow over days or weeks
• One node enlarged (localized) vs. multiple or generalized enlargement
• Warmth or tenderness when touched in some cases

• Mild: Slightly enlarged, often from dental disease or local infection
• Moderate: Noticeably swollen, possibly from systemic infection
• Severe: Large, fixed, or rapidly growing nodes—may suggest lymphoma or other serious disease

Common Causes of Swollen Lymph Nodes in Dogs

1. Bacterial or viral infections – Infections trigger lymph nodes to filter pathogens and produce immune cells, causing temporary swelling. Often seen with: fever, lethargy, reduced appetite. Breeds: Any; young or immunocompromised dogs may be more affected.

1. Dental or oral disease – Infections or abscesses in the mouth drain to nearby submandibular lymph nodes. Often seen with: bad breath, difficulty eating, pawing at mouth. Breeds: Small breeds prone to dental issues (Chihuahuas, Yorkshire Terriers).

1. Tick-borne diseases – Lyme disease, ehrlichiosis, or anaplasmosis cause lymphadenopathy as the immune system responds. Often seen with: fever, lameness, joint swelling. Breeds: Dogs in endemic tick areas.

1. Allergies or skin infections – Dermatitis or skin infections can cause regional lymph node enlargement where they drain. Often seen with: itching, hair loss, skin lesions. Breeds: Breeds prone to allergies (Golden Retrievers, Bulldogs).

1. Lymphoma – Cancer of the lymphocytes; lymph nodes become enlarged, often firm and non-painful. Often seen with: lethargy, weight loss, enlarged spleen or liver. Breeds: Golden Retrievers, Boxers, Bullmastiffs have higher risk.

1. Other cancers – Metastatic cancer can spread to lymph nodes, causing enlargement. Often seen with: depends on primary tumor site. Breeds: Varies by cancer type.

1. Fungal infections – Blastomycosis, histoplasmosis, or valley fever can cause lymphadenopathy. Often seen with: respiratory signs, skin lesions. Breeds: Dogs in endemic regions.

1. Immune-mediated disease – Conditions like immune-mediated polyarthritis may involve lymph node enlargement. Often seen with: joint pain, fever. Breeds: Varies.

1. Reaction to vaccination – Lymph nodes near injection sites (e.g., neck) may briefly swell after vaccines. Often seen with: mild swelling, resolves within days. Breeds: Any.

1. Parasitic infections – Leishmaniasis or other parasites can cause lymphadenopathy. Often seen with: skin changes, weight loss. Breeds: Dogs in endemic areas.

When Is Swollen Lymph Nodes an Emergency?

Seek emergency care if your dog:

• Has rapidly growing or very large lymph nodes
• Shows severe lethargy, difficulty breathing, or collapse
• Has multiple swollen nodes with fever, not eating, or weakness
• The node is red, hot, draining, or the skin over it is broken
• Has sudden onset with high fever or signs of sepsis

How Veterinarians Diagnose the Cause

Diagnostic steps typically include:

1. Physical exam – Palpation of all accessible lymph nodes for size, shape, consistency, pain, and mobility

1. Fine-needle aspiration (FNA) – A needle withdraws cells from the node for microscopic review; helps distinguish infection from lymphoma

1. Blood work – CBC, chemistry, and tests for tick-borne diseases or other infections

1. Biopsy – Surgical removal of a node or tissue sample for definitive diagnosis, especially if cancer is suspected

1. Imaging – X-rays or ultrasound to check for internal node involvement, organ enlargement, or masses

1. Culture – If infection is suspected, fluid or tissue may be cultured for bacteria or fungi

Treatment Options

Treatment depends entirely on the cause:

At home, avoid squeezing or aggressively manipulating swollen nodes. Follow your vet's treatment plan and return for rechecks as recommended. If your dog is diagnosed with lymphoma or another cancer, your vet will discuss staging, prognosis, and long-term care options. Many dogs with lymphoma respond well to chemotherapy and can enjoy good quality of life for months to years. For infectious causes, ensure your dog completes the full course of antibiotics or other medications to prevent relapse.

Prevention Tips

• Keep your dog on year-round flea and tick prevention
• Maintain good dental care with brushing and professional cleanings
• Keep vaccinations current to reduce infectious causes
• Perform regular checks for lumps while petting or grooming
• Ensure a balanced diet and healthy weight to support immune function
• Minimize exposure to endemic fungal regions when possible

Frequently Asked Questions