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Ask a Vet: Causes of Swollen Lymph Nodes in Dogs

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Causes of Swollen Lymph Nodes in Dogs

The causes of swollen lymph nodes in dogs are various and require investigation by a veterinarian. In order to better understand what may trigger a dog's lymph nodes to enlarge it helps to take a closer insight into what functions a dog's lymph nodes have and how they react to challenges to a dog's body. Veterinarian Dr. Ivana Crnec discusses lymph nodes in dogs and several causes of swollen lymph nodes in dogs.

dog watermelon

Swollen Lymph Nodes in Dogs 

The lymph nodes or lymph glands are part of the lymphatic system (circulatory network that carries fluid called lymph and both produces and transports white blood cells).

Lymph nodes are an integral part of the dog’s immune system. As small tissue masses, lymph nodes can be found throughout the dog’s body. Lymph nodes can be classified as external and internal.

The external lymph nodes can be palpated from the outside because they are positioned just beneath the skin. Internal lymph nodes are found in the abdominal and chest cavity and can only be visualized through specific imaging techniques.

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In a nutshell, lymph nodes have two crucially important roles: 1) filtering the blood, and 2) storage of white blood cells. Lymph nodes act like first responders – they are the primary indicator that a threat or disease is present. Lymph nodes are important because they mediate the body’s response to diseases, allergic reactions and autoimmune threats.

Causes of Swollen Lymph Nodes in Dogs

 This dog shows swelling of the submandibular lymph nodes

This dog shows swelling of the submandibular lymph nodes

When a threat is presented, white blood cells accumulate in the lymph nodes. Their aim is to combat the threat. The increase accumulation or influx of white blood cells lead to enlargement of the lymph nodes.

More precisely speaking, the causes of enlarged lymph nodes in dogs can be classified as: bacterial causes including streptococci, septicemia, brucella canis, rickettsial causes including ehrlichiosis, salmon poisoning, fungal causes including histoplasmosis and aspergillosis, parasitic causes including babesiosis and toxoplasmosis.

Viral causes may include infectious diseases such as canine hepatitis and canine viral enteritis.

Non- infectious causes may include drug reactions, immune mediated disorders, rheumatoid arthritis. Neoplastic causes or infiltrative may include mast cell tumor, leukemia and multiple myeloma. Non-neoplastic causes may include mast cell infiltration and eosinophilic granuloma complex.

If your dog’s lymph nodes are enlarged, swollen or otherwise altered in general appearance, it is highly recommended to consult your trusted vet for a proper diagnosis and compatible treatment.

Enlarged lymph nodes can also be classified based on their range of extent in the body and based on their affection of the adjacent tissues. Based on the range of extent, the condition can be classified as:

  • Solitary – when a single lymph node is enlarged
  • Regional – the lymph nodes in a particular and specific area are enlarged but they do not interconnect
  • General – more than one body areas have enlarged lymph nodes which may be interconnected.

Based on the affection of adjacent tissues, the condition can be classified as superficial or deep.

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Lymphadenitis in Dogs 

When the lymph nodes are swollen due to an infection or inflammation, the condition is medically termed as lymphadenitis. Infections arise from infectious agents while inflammation develops when an injury provokes a local tissue reaction.

In both cases, the lymph nodes become enlarged due to increased accumulation of white blood cells which are supposed to combat the infectious or inflammatory agent.

Bacterial infections are particularly common among dogs. The most frequent causative agent of bacterial infections and consequently enlarged lymph nodes are representatives of the Streptococcus species.

Strep Throat in Dogs 

The most common bacterial infection in dogs is inflammation of the tonsils caused by Streptococci (consequently the condition is popularly known as Strep-throat). During a strep-throat the dog’s lymph nodes in the neck area become particularly enlarged and the dog shows symptoms like coughing, fever, pain and lethargy.

Due to their developing immune systems young dogs are more prone to strep-throat than grown up dogs with fully developed immunities. Fortunately, strep-throat is curable (antibiotics, plenty of fluids and rest) and easily preventable.

It should be noted that here are other bacterial and nonbacterial infectious agents that can cause similar symptoms. Therefore, it goes beyond saying that you should have your dog checked by a veterinarian.

lump on a dog's throat

A dog with lymphoma

Lymphadenopathy in Dogs 

The medical term used for enlarged lymph nodes is lymphadenopathy. The most common causes of lymphadenopathy in dogs are lymphoma and leukemia.

Lymphoma (Cancer of the Lymph Nodes)

Lymphoma is the most commonly diagnosed type of cancer in canines. The term lymphoma describes a variety of cancers that originate from the lymphocytes (type of white blood cells responsible for fighting off infections). Based on their aggressiveness, clinical signs and survival rates, lymphomas can be classified as: multicentric, alimentary, mediastinal and extranodal.

Multicentric lymphomas are by far the most common type. In fact 80 to 85 percent of the diagnosed lymphomas are classified as multicentric. Multicentric lymphomas affect the lymph nodes and as a result the lymph nodes become rapidly enlarged. Sometimes the affected lymph nodes may become 3-10 times larger than normally. The enlarged lymph nodes feel like painless and firm but rubbery lumps that move beneath the skin.

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Dogs with multicentric lymphomas may show signs like anorexia, lethargy, fever, weakness and dehydration. To diagnose the condition, the vet will take a small sample from the dog’s lymph nodes and evaluate the sample’s cells under a microscope. The most effective treatment is chemotherapy. Depending on the exact type of lymphoma and the dog’s overall health status, the vet may suggest additional treatment such as radiation and surgery.

Differential Diagnosis of Swollen Lymph Nodes in Dogs

The tissue sample taken from the liver is checked under a microscope.

Samples taken from lymph nodes are checked under a microscope.

Every routine physical examination includes palpation of the external lymph nodes. Untrained dog owners may find this task hard, but when it comes to veterinary professional determining enlarged lymph nodes is quite easy. In fact, most lymphadenopathies are discovered by accident when dogs are brought to the vet’s office for some other reason.

Lymph nodes that are enlarged due to infection or inflammation are tender and more or less painful while the surrounding area is warm. On the flip side, lymph nodes with neoplastic changes are hard and painless. These signs are not enough to set the right diagnosis.

Setting the right diagnosis includes examining some of the lymph node tissue under a microscope. Some lymph nodes can be removed completely, while for larger ones, your vet may either remove a small piece of abnormal tissue (known as taking a biopsy) or use a needle and syringe to withdraw a sample of cells from the tissue (fine-needle aspiration). Regardless of the technique, the sample is analyzed under a microscope.

About the Author

ivana crnec

Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia. She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.

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Photo Credits:

Wikipedia This is a 12 year old Golden Retriever with lymphoma. The left submandibular lymph node is swollen photo by Joel Mills, license: Creative CommonsAttribution-Share Alike 3.0 Unported

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