Lymph Node Diseases of Animals
The lymph nodes are part of the lymphatic system. They have several important functions regarding the immune system, and are good indicators of disease. The mammalian body has many internal lymph nodes. These can only be visualized by exploratory surgery, a CT scan, an MRI, a radiograph, or an ultrasound. The lymphatic system is part of your dog’s immune system. It includes lymph nodes and a network of lymph vessels called lymphatics that run alongside your dog’s regular blood vessels. The lymph system performs several important functions in your dog’s body, including transporting white blood cells, removing waste products from tissues and cells, and helping to produce disease-fighting antibodies.
Lymph nodes are small, bean-shaped organs that contain immune cells. When your dog’s body is invaded by viruses or bacteria, or your dog has a disease that triggers an immune response, the lymph nodes become enlarged as they work to fight off the invader. Swollen lymph nodes are called lymphadenopathy or lymphadenomegaly.
Lymph nodes, sometimes referred to as lymph glands, are an important part of the immune system. Lymph nodes are clustered throughout the body and function as filters, removing foreign particles from fluids that run through the vessels of the lymphatic system.
Within lymph nodes are white blood cells called lymphocytes that help neutralize foreign agents like bacteria. Swollen lymph nodes are a sign that the body is fighting infection, and they may be tender and painful. In some cases, swollen lymph nodes may be a sign of cancer.
Lymph nodes are very important anatomical structures. Lymph nodes can be found by careful palpation to identify these small soft structures. The palpable lymph nodes are called peripheral lymphnodes. Peripherial indicates that they are on the outside. Internal lymph nodes are present, but unless they are very large, they cannot be felt. Lymph nodes are located at points of the lymphatic system. The lymphatic system is a system of very thin walled vessels that carry lymph. Lymph is fluid that circulates through the entire body much like blood. Lymph flow is essential to life yet is one of the least understood systems of the body. Lymph fluid is composed of water, proteins (antibodies) and lymphocytes. Lymphocytes are the white blood cells responsible for producing antibodies. The lymph fluid circulates but does not have a pump like the heart for circulation. Lymph circulates by the action of muscles and takes advantage of other areas of the body such as the negative pressure of the chest cavity. When limbs do not move the lymph flow stagnates which leads to swelling. The fluid present in such swelling is usually lymph. Lymph nodes are located strategically along the lymph circulatory system. These nodes house many lymphocytes, which process antigen for antibody production. Lymphnodes become very active in the production of antibodies for a diseased organ which it receives the lymph drainage from. If you have an abscessed tooth on your left jaw, then the lymph node under that jaw will be inflamed. That is it is trying to build antibodies to fight the infection in your jaw. When we have strep throat our lymph nodes in our neck are enlarged. The lymph node will capture the draining fluid from an infected organ and process the foreign material to use to make antibodies to protect the body. Therefore, we need to learn to feel for the lymph nodes that drain various parts of the body. Enlargement of these nodes can give us an indication of disease of these regions. If a lymph node is enlarged, it can be biopsied to help determine the type of disease process that is occurring.
For example, dogs with Demodex will actually have mites present in their lymph nodes. Pets with bacterial infections will have bacteria within their lymph nodes. Dog Lymph nodes should be small, soft and non-painful. If a lymph node is hard, hot, or painful then a concern about that region of the body is developed. The common locations for the peripheral lymph nodes in dogs are the cervical nodes under the back of the jaw, the pre-scapular which are between the shoulder and the neck. The axillary lymph nodes are under the front legs and the inguinal lymph nodes are in the inguinal region of the back legs. The popliteal nodes are behind the knee. Please practice feeling for these nodes, it would be great for you to be responsible for finding a previously unknown infection or other illness. Lymph nodes are also enlarged in cancer. Leukemia is cancer of the lymphocytes and can be put in remission if caught early. Other cancers can be diagnosed by biopsy of an affected lymph node. Lymph node removal has been shown to slow the growth of cancer in an area as well. Poorly functioning lymphatics (lymph vessels) cause swelling or edema of an organ. The largest lymph vessel is called the thoracic duct and is located in the chest. Rupture of this duct occurs in dogs and cats and causes a condition called chylothorax. This is a white fluid (lymph) which floods the chest causing the animal to have severe breathing problems. Surgical ligation of the thoracic duct may be helpful. Congenital absence of the lymphatics is also possible and can occur in the intestines. The lymph in the intestines absorbs a large amount of the fat that we eat and absence of the lymphatics (lymphangiectasia) is a serious cause of diarrhea in young affected dogs (this condition is rare). W/D food is used for this disease.
White blood cells apart from some lymphocytes are produced in the bone marrow. The white blood cell act to protect the body from disease. White blood cells are the policemen of the body. Just as there are different types of policemen there are different types of white blood cells.
Neutrophils
Neutrophils are the first on the scene when invaders are detected. When the body detects foreign invaders it sends out a chemical signal that attracts the neutrophils. The can move through the blood vessel walls to get to wherever they are needed. They contain granules which kill bacteria and viruses. The life span of a neutrophils is very short, only 8 hours.
Macrophages/Monocytes
Monocytes are circulating cells macrophages are found in the tissues. These are the Crime Scene Investigators. They inspect the scene of the crime after the neutrophils have killed something and pick up the antigens and take them back to the lymph node. They are five times as big as a neutrophil.
Eosinophils
Like the neutrophil the eosinophil contains granules, the difference being that the granules stain red instead of purple. Allergic reactions are caused by mast cells degranulating. Eosinophils neutralize the mast cells. Their job is to fight parasites and allergies. Eosinophils live for 24 – 35 hours.
Basophils
Basophils have blue staining granules. They are a second line of defense against parasites and allergies and are present in severe allergic and parasitic infections.
Lymphocytes
Only 10% of lymphocytes are in the circulation. They prefer to stay at headquarters and analyze the evidence and synthesize new antibodies to fight infection. B-lymphocytes are produced in the bone marrow. T-lymphocytes are produced in the thymus. T-lymphocytes act like smart bombs and kill specific invaders. B-lymphocytes manufacture antibodies. Lymphocytes are very long lived and are capable of division or transforming into more active forms in the lymph node.
Lymph nodes
Lymph nodes act as police headquarters collecting the evidence (antigens) from the macrophages and producing antibodies to fight disease.
Your vet can tell the difference between swollen lymph nodes and regular lymph nodes by feeling the lymph nodes that are closer to the skin. Lymph nodes that can be felt through the skin are known as “palpable” nodes. These are located in a few areas:
- Submandibular: Just under the jaw where it meets the neck
- Pre-scapular: Under the submandibular lymph nodes at the front of the shoulders
- Axillary: In the “armpit” of the dog, or where the front legs meet the chest
- Inguinal: On the underside of the dog where the rear legs meet the abdomen (groin)
- Popliteal: Just behind the stifles (“knees”) of the rear legs
During a physical exam when your veterinarian looks like she is petting your dog, she is actually feeling for abnormalities in the lymph nodes, as well as unusual lumps or bumps. Generally, the only palpable lymph nodes are the submandibular and popliteal in a healthy dog.
Symptoms of Swollen Lymph Nodes in Dogs
Swollen lymph nodes can sometimes be detected by pet parents at home. If you’re petting your dog and feel a new or unusual bump in one of the areas listed above, it may be a swollen lymph node.
In most cases, there are no outward symptoms that accompany your dog’s swollen lymph nodes, particularly if they are only mildly enlarged. However, if the lymph nodes are significantly enlarged—including the nodes inside the thorax and abdomen— then you should watch for symptoms including:
- Vomiting
- Coughing
- Lethargy
- Fever
- Poor appetite
- Enlarged abdomen
Causes of Swollen Lymph Nodes in Dogs
Lymph nodes enlarge when the immune system is activated, usually by a disease process. If just one or two lymph nodes are enlarged, this often indicates a localized disease. For example, an infected toe could result in enlarged lymph nodes that drain that area.
A systemic infection in which the whole body is affected will often cause many or all of the lymph nodes to be enlarged. Examples include:
- Demodectic mange
- Puppy “strangles” (i.e., juvenile cellulitis)
- Tick-borne diseases (e.g., Lyme disease, ehrlichiosis)
- Bacterial infection (e.g., Yersinia pestis, which causes canine plague)
- Reactive hyperplasia (e.g., active immune response)
- Fungal infection (e.g., Coccidioidomycosis)
- Immune-mediated diseases (e.g., pemphigus)
- Cancer (e.g., lymphosarcoma)
Dog Breeds Prone to Swollen Lymph Nodes
There aren’t specific breeds that are susceptible to swollen lymph nodes. However, some breeds are susceptible to diseases that will cause swollen lymph nodes. Other breeds are prone to developing lymphosarcoma (cancer of the lymphatic system), including Golden retrievers, Boxers, Dobermans, Rottweilers, and others.
Toy breeds (such as Yorkies, Poodles, and Dachshunds) are very susceptible to dental disease, and often have enlarged submandibular lymph nodes when they have infected teeth and gums.
In most cases, your dog’s lifestyle is a better predictor of their susceptibility to certain diseases that cause enlarged lymph nodes. For example, a hunting dog or a dog that spends a lot of time in the woods is far more likely than an indoor dog to contract tick-borne diseases like Lyme disease and ehrlichiosis, as well as fungal, bacterial, or parasitic diseases that can lead to enlarged lymph nodes.
How Vets Diagnose Swollen Lymph Nodes
Enlarged lymph nodes are usually fairly obvious on physical exam. If your vet finds swollen lymph nodes, they may collect a sample through one of these methods:
- FNA: Fine needle aspirate (FNA) is a procedure in which a syringe and needle are used to collect cells that can be examined under a microscope. Your vet will examine these cells on a slide, or they might send the sample out to an external lab for analysis.
- Biopsy: Your vet may decide instead to perform a biopsy under general anesthesia. In this procedure, a larger piece of the lymph tissue is removed for analysis by a histopathologist. Usually the histopathologist’s diagnosis is available in 7-10 days.
Treatment for Swollen Lymph Nodes
Treatment of swollen lymph nodes depends on the underlying cause. Sometimes your vet may start treatment for your dog before receiving a confirmed diagnosis from histopath. This is usually done if your vet is certain of the diagnosis. Treatment might include:
- Antibiotics
- Antifungals
- Anti-inflammatories
- Steroids
- Surgery
If cancer is confirmed, chemotherapy may be started.
What causes swollen lymph nodes in dogs?
- Tick-borne diseases. Make sure that if your dog is exposed to ticks that you have them on an effective tick control product. Speak with your vet about what product is right for your dog based on their medical history.
- Foreign bodies such as plant awns in feet. Do not let your dog wander off-leash, especially in an area with longer grass.
- Fungal and bacterial diseases. Avoid letting your dog wander while unleashed. This will help minimize contact with fungal and bacterial diseases.
- Cancer (lymphosarcoma). Be aware of what is “normal” for your dog’s lymph node size. Report any abnormal swellings to your vet as soon as you notice them. Be extra wary if your dog is a high-risk breed such as a Golden Retriever, Boxer, Doberman, or Rottweiler.
- Immune-mediated diseases such as pemphigus.
What do swollen lymph nodes in dogs feel like?
Swollen lymph nodes feel like grapes just under the skin surface. They can double in size overnight with diseases like lymphosarcoma.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
Image-Courtesy-Google
Reference-On Request.
