How Lymph Nodes on Dogs Work and Why They're Important

What is the Lymphatic System? 

The lymphatic system is an important part of your dog’s body’s ability to keep itself safe from toxins and sicknesses. It provides the body with a separate path for fluid to move from tissue to tissue without being in the bloodstream, as there are some things that the bloodstream wouldn’t benefit from or simply can’t transport on its own. Substances like proteins, fats, white blood cells, and waste products are transported through the lymphatic system.^1,2

The purpose of the lymphatic system is to keep your dog’s internal ecosystem clean and protect and defend your dog’s immune system. 

There are several organs that make up the lymphatic system: the lymph nodes, lymph,  gut-associated lymphoid tissue (GALT), thymus, bone marrow, and spleen.^1,2  

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Parts of the Lymphatic System

Lymph Nodes: 

Lymph nodes are the main touch points of the lymphatic system, they are small glands found around the body that act as checkpoints for the lymph to pass through. Lymph nodes are connected throughout the body with vein-like structures to allow the lymph fluid to pass and for waste, nutrients, and oxygen to be passed to cells throughout the body. 

Lymph nodes are signalers to vets and pet parents alike that there may be a threat to a dog’s health, so we will go into more detail on them in this post. 

Lymph Fluid 

Lymph fluid, often simply called lymph, is a milky fluid that flows through the lymphatic system. It is the transport vessel for all of the cells, proteins, fats, and waste that the lymphatic system manages in your dog’s body. Lymph flows through lymphatic capillaries that are easily passable, allowing it to trap pus, metabolic wastes, dead cells, and other pathogens.

Lymph is what allows the lymphatic system to work twofold, by both being a vessel that can remove the unwanted materials in the body and also providing another way for the body to provide necessities throughout the system without overburdening the bloodstream. It takes away fats and oils from your small intestine, using something called the Gut-Assocoated Lymphoid Tissue (GALT). Then, it moves them through special nodes in your body to be cleaned up by your liver. The healthy stuff goes back into your blood. It also gets rid of other bad things like fungi, viruses, and chemicals from your body.²

Lymph isn’t pumped the same way that blood is because it is not connected directly with the heart. Lymph is manually stimulated through movement in the body, so to keep the lymph moving through the system to remove waste and keep up on immune system defenses, it is important to keep your dog active.

Gut-Associated Lymphoid Tissue (GALT)

GALT is just the tissue located throughout the GI tract that works on behalf of the lymphatic system; it is present in the tonsils and intestines and is part of the larger mucosa-associated lymphoid tissue (MALT). 

Thymus

The thymus is a part of the lymphatic system that is located in the front of the chest cavity, it’s between the windpipe and ribs, in front of the heart. The thymus is a location in the body where T-cell lymphocytes are able to get stronger and multiply. T-cells are one of the main forms of immune system defense cells.⁶ 

Bone marrow

Bone marrow is inside of the center of a bone, usually more present in the long bones of the body, like the limbs. Bone marrow is an important part of the immune system because it is where the body develops and produces white and red blood cells. Those white and red blood cells are the body’s main defense against infections and foreign substances.²

Spleen

The spleen, which is located near the stomach, is the largest part and is sometimes considered the start of the lymphatic system. The spleen filters blood, rather than lymph fluid, and has lymphatic tissues.¹ 

The lymphatic tissue in the spleen does two things, the first is that it holds B- and T-cell lymphocytes close to filter the blood that comes through the spleen. B-cells create antibodies to fight infections and T-cells attack pathogens in the blood. The second thing the lymphatic tissue in the spleen does is help store blood platelets and remove faulty red blood cells from the blood to keep everything moving smoothly.²

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The Importance of Lymph Nodes on Dogs

There are over a hundred lymph nodes throughout a dog’s body, but there are only a handful of which that can be felt by a pet parent or a vet, and those are often the ones that are able to be diagnosed if there is a problem. 

Lymph nodes are located throughout the entire body and act as stopping points for the lymph fluid to check in so that if there is too much waste or infectious cells in the fluid, they can be dropped off in the lymph nodes. So if a lymph node starts to swell that is often a clear sign that your dog is fighting off an infection.¹ 

Where are the lymph nodes you can check?

There are 5 sets of lymph nodes that are located on the outer part of the body, closest to the skin, which makes them easy to feel and check for their size. Lymph nodes are located in groups and feel like a small, round, or sometimes bean-like shape under your dog’s skin. Generally, you should not be able to feel them unless you are consciously looking for them; in small dogs, a healthy lymph node will be about the size of a pea, and in large dogs, it should be about the size of a grape.³ 

The 5 places that you can feel lymph nodes on your dog are:^3,4,5

1. On either side of your dog’s jaw where the neck and jaw meet. (Submandibular lymph nodes)
2. In front of the shoulder blade, where the neck and shoulder meet near the chest (Prescapular lymph nodes)
3. In the armpit (Axillary lymph nodes) 
4. In the groin area (Inguinal lymph nodes)
5. At the back of your dog’s knee (Popliteal lymph nodes) 

What do canine lymph nodes do?

The lymph nodes are a location in the body that houses lymphocytes and allows them to work on the bacteria, viruses, and cancer cells in the lymph fluid. Thanks to the lymph nodes, there is a site for white blood cells to organize an attack on the foreign substances and not allow them into the bloodstream.^1,2 

Healthy lymph nodes are incredibly important for your dog’s overall health and well-being, if they are not working properly it is entirely possible that your dog may be more susceptible to disease or infection. 

The lymph nodes trap and remove waste and excess fluids from the body; they destroy bacteria and protect the entire body. 

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Swollen lymph nodes on your dog: What does it mean?

There are a number of reasons that a lymph node will swell, and all are signs that your dog is fighting off infection but not all of them will be life-threatening. No matter what, if you find a swollen lymph node, or if you think a lymph node may be swollen, please have your vet check it out for your dog’s health and safety.²

Potential causes of swollen lymph nodes

A swollen lymph node can be called lymphadenopathy, there are many causes for lymphadenopathy to occur. 

Cancer is one of the most dangerous potential causes of a swollen lymph node. Lymphoma or lymphosarcoma affects the lymphocyte cells directly and requires treatment immediately after receiving a diagnosis. Currently, it is not a curable cancer but with treatment, a dog with lymphoma can achieve remission and live a happy life.^1,2,3,4 

Other than cancers of the lymphatic system itself, some swollen lymph nodes can be caused by cancer developing near that node. For example, if there is dental cancer developing then the submandibular lymph node below it may swell. This swelling could be reacting to the local inflammation, or it could be a sign the local cancer has spread into the lymph node.

Infections are also another common cause of a swollen lymph node. Lymph nodes swell when there is a need for more white blood cells to defend the area. More white blood cells can be needed for a number of reasons—wounds, skin infections, fungal infections, and tick-borne diseases (such as Lyme disease and others).^3,4

Allergies can also cause swollen lymph nodes. Allergic reactions to food, environments, and fleas can all lead to the lymph nodes working to filter out that unwanted input.^3,4,5 

Autoimmune diseases can sometimes lead the system to mistakenly attack healthy tissue and cells, leading to swollen lymph nodes.^4,5 

Medications and vaccinations can cause the lymph nodes to swell and react as well, but that reaction is extremely rare. Medications like antibiotics, anticonvulsants, and vaccinations used to introduce a virus to the body will trigger a response from lymph nodes and is not always a call for concern.⁴ 

Other localized infections, such as an ear infection, respiratory infections, or dental disease may lead to the lymph nodes located closest to the active infection swelling as they work to defend that area.⁴ 

Physical trauma to the lymph node can also result in swelling, just as bruising and swelling can occur on any part of the body due to physical trauma.^4,5

Symptoms of swollen lymph nodes

For many dogs, swollen lymph nodes will be the symptom that says something is wrong and needs to be checked out. While others may have other symptoms along with it, if you notice swelling, that should be enough to take your dog to the vet.^3,4 

• Discomfort when area is touched
• Fever
• Loss of appetite or weight
• Lethargy
• Coughing/sneezing/difficulty breathing 

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Diagnosis and Treatment for Swollen Lymph Nodes on Dogs

Diagnosis 

The first step to diagnosing and treating any illness is always going to be to find the cause of the symptom. Because swollen lymph nodes will not always mean cancer for dogs, a vet will start with simple diagnostic procedures and perform additional tests as needed. 

For most vets, that first step will be to get a sample, whether it be blood or direct fluid from the swollen lymph node.

To get a sample from the lymph node your vet will perform an FNA, or fine needle aspirate. The FNA will allow them to look at the sample under a microscope and see what the cells look like. The fluid will show the presence of cancer cells, bacteria, or other forms of abnormal cells.^3,4 

If your vet takes a blood sample they will perform a blood test called the complete blood count (CBC) and chemistry which will help create a biochemical profile on the dog’s underlying health problems. The biochemical profile will measure organ function and can also rule out many infections, as well as cancer, from the reason behind the swelling.^4,5

If there is a reason for your vet to suspect cancer then the next step can often be a biopsy of the tissue in the lymph node. A biopsy is the most definitive way to diagnose a lymph node problem and rule out cancer, or determine the extent and type of cancer that your dog may be facing.⁵ 

Other tests that some vets may perform include diagnostic imaging like x-rays and ultrasounds to assess the size and shape of the lymph nodes, and urinalysis to test the urine for any abnormal cells and substances that would lead to a diagnosis.^3,5

Treatment options

Treatment will, of course, depend on the cause of the swelling, and you will have to trust that your vet has done the testing needed to find the most effective treatment. 

For dogs with dental problems, infections, or diseases that have caused the swelling, a dental procedure may be necessary. Anything from cleaning a dog’s teeth to removing diseased ones. They could also be given antibiotics or antifungal medication to help the lymph nodes defend against the infection. It should be noted that it will take some time after treatment for the lymph nodes to return to their normal size once the infection is managed, anywhere from a few days to a few weeks.³ 

For dogs with cancer, specifically lymphoma, the most effective treatment will be a multi-agent chemotherapy protocol. Over time, this treatment will lessen the swelling and in best case situations bring the dog into remission, allowing them to live happily and comfortably for that period of time. Chemotherapy for dogs is designed to help them live comfortably during treatment and doesn’t have anywhere near as many side effects as human chemotherapy treatments will. 

You can learn more about chemotherapy treatments for canine lymphoma on our blog.

For dogs with other cancers that have cells affecting the lymph nodes, treatment can vary depending on what the best option is for that type. For some cases, surgery will be the best option, while others may respond best to radiation or chemotherapy drugs. 

Other medications may be prescribed for the various other reasons that a lymph node will swell. For dogs with autoimmune diseases, immunosuppressive drugs may be given to help the immune system work at the right level and lower the swelling. For dogs with bacterial infections, antibiotics can be prescribed to help the lymph nodes fight off the infection and lessen their burden, thus bringing the swelling down.⁴ 

Preventative care - Stop the swelling before it starts 

Keeping your dog’s lymph nodes healthy will keep their whole body healthy. It’s always important to keep these things in mind as a pet parent, but if swollen lymph nodes are not something you want to worry about, then adding some of these practices to your routine may benefit your dog greatly.⁴ 

Keep up with their vaccinations: why let sickness in when you don’t have to? Let your dog’s immune system learn the best way to defend itself from common illnesses so it doesn’t have to work so hard in the future. 

Routinely visit your vet for check ups: with most health factors, catching something early is the easiest way to prevent trouble. Going to the vet regularly to have your dog checked out for a good bill of health is a great way to find out if something might be up before it shows symptoms—or else treat it before it becomes a real problem.

Brush your dog’s teeth: A lot of lymph node problems stem from dental issues, keeping your dog’s teeth clean will help them stay healthy and put less bacteria into the body over time. The best practice would be to brush your dog’s teeth daily, but you can work your way up to that, getting yourself and your dog used to the activity. 

Regular exercise: The lymphatic system doesn’t have a pump that keeps it moving the way that blood does. Exercise will keep the lymph fluid moving through your dog’s body so that you won’t have to worry about toxins or waste building up. 

Flea and tick prevention: With the amount of damage that a tick-borne disease can cause, protecting your dog from them with prevention is the easiest way to stop the danger before it starts. Find the most effective flea and tick prevention that you can keep track of and regularly give, as well as one that is an appropriate defense to your area. If you live somewhere that has a tick problem, be sure to talk to your vet about the flea and tick prevention method you are using. 

Limit exposure to toxins: While it’s not entirely possible to prevent cancer, lessening your dog's interaction with things that might cause cancer will be your best bet to having some control over it. Try to limit, or entirely avoid, any interactions between your pet and pesticides or other strong chemicals, as these have been shown to increase the risk of cancer development.

Learn about how ImpriMed helps vets find the best canine lymphoma treatment possible for each individual patient.