Lymph nodes (or glands), are small masses of tissue that can be found throughout the body. They play an integral part in the functioning of the dog's immune system, acting as filters for the blood, and as storage places for white blood cells. Consequently, they are often the first indicators of disease in the tissues.
When tissues become inflamed, the regional lymph nodes that these tissues drain into will also become inflamed and swollen in response. This swelling is due to a reactive increase in white blood cells (hyperplasia) due to the localized presence of an infectious agent. This is medically defined as reactive hyperplasia: when white blood cells and plasma cells (antibody secreting cells) multiply in response to a substance that stimulates their production (antigenic stimulation), causing the lymph node to enlarge.
Lymphadenitis is a condition in which the lymphatic glands have become inflamed due to infection. Neutrophils (the most abundant type of white blood cell, and the first to act against infection), activated macrophages (cells which eat bacteria and other infectious agents), and eosinophils (cells which fight parasites and allergy causing agents) will migrate into the lymph node during an episode of lymphadenitis. This convergence of cells results in the swollen feel and appearance of the nodes.
Cancerous cells may also be found in a lymph node biopsy (tissue sample). Cancer cells may be primary, originating in the lymph node (malignantlymphoma), or may be there as a result of the spread of cancer from another location in the body (metastasis).
Symptoms and Types
Lymph nodes can usually be detected by touch, but sometimes there will be no clinical symptoms. Swelling can be felt in the area beneath the jaw (submandibular), or around the shoulder. Swelling in one of the legs is also possible as a result of swollen lymph nodes at the back of the leg (popliteal), or near the joint of the leg (axillary – correlating with the armpit). Swollen nodes in the area near the groin (inguinal) may make defecation difficult for your dog. Your dog may also lose its appetite due to nausea, and have an urge to regurgitate when it does eat. You can also expect your dog to feel a general malaise as its body fights off the infection. If your dog has severely enlarged lymph nodes it may have trouble eating, or have difficulty with breathing.
Lymphoid hyperplasia: when lymph nodes react to an infectious agent by producing an excess of white blood cells, but are not themselves infected
Lymphadenitis: when the lymph nodes themselves are infected either primarily or secondarily
Sporotrichosis: fungal infection of the skin, acquired from soil, hay, plants (most notably, garden roses); affects the skin, lungs, bones, and brain
Rickettsia: transmitted by ticks and fleas
Bartonella spp: transmitted by biting flies
Brucella canis: sexually transmitted; acquired during breeding
Pasteurella: transmitted through the respiratory system
Yersinia pestis : transmitted by fleas and possibly rodents; also known as the plague
Fusobacterium: infection of the mouth, chest, throat, lungs
Francisella tularensis: tularemia; transmitted by ticks, deer flies, and by the dispersion of gases from an infected animal carcass (frequently occurring during lawn-mowing)
Mycobacterial: transmitted by infected water supply
Allergens: lymph glands respond to an allergic reaction in the body by producing more cells – usually occurs in the lymph nodes near the site of the reaction
Immune-mediated disease: the body’s immune system over-reacts to an invasion, or reacts inappropriately
Eosinophilic infiltration: multiplication of white blood cells responsible for controlling allergy response, or for fighting parasitic agents
Canine hypereosinophilic syndrome: excessive eosinophils, may be associated with leukemia, blood marrow infection, asthma, or allergy
Your veterinarian will perform a thorough physical exam on your dog. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, an electrolyte panel, urinalysis, and a blood smear.
Lymph node aspirates (liquid) will also be taken for microscopic (cytologic) examination. Abnormal tissue growth, or tumors (neoplasia), and fungal infections can also be confirmed via cytologic examination of lymph node aspirates.
You will need to give a thorough history of your dog's health, including a background history of symptoms, and possible incidents that might have precipitated this condition. The history you provide may give your veterinarian clues as to which organs are causing secondary enlargement of the regional lymph nodes.
Other useful blood tests include serologic (blood serum) tests for antibodies against systemic fungal agents (Blastomyces and Cryptococcus), or bacteria (Bartonella spp.). Radiograph and ultrasound imaging will allow your doctor to visually inspect the affected lymph nodes, and may also enable detection of lesions associated with lymph node enlargement in other organs.
Your veterinarian will prescribe medication dependent on the underlying cause of the lymph node enlargement.
Living and Management
Some infections are zoonotic, meaning that they can be transmitted to humans. Systemic diseases, like sporotrichosis, Francisella tularensis, Yersinia pestis, and Bartonella spp, are zoonotic. If your dog has one of these zoonotic diseases, ask your veterinarian what precautions you will need to take to avoid infection.
Something that becomes worse or life threatening as it spreads
General discomfort of the body
A term for a type of neoplasm that is made up of lymphoid tissue; these masses are usually malignant in nature
The growth of pathogens away from the original site of the disease
Underneath the lower part of the jaw
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
Something that is related to the whole body and not just one particular part or organ
Anything pertaining to the blood vessel system in the body
Returning food that has been swallowed into the mouth; often results in vomiting
A medical condition in which the lymph nodes are inflamed
The process of removing tissue to examine it, usually for medical reasons.
The area under the arm; the arm pit.
An allergic disorder that results in difficulty breathing.
The exiting of excrement from the body; bowel movements.
The area between the abdomen and thighs; the inguinal area
Small structures that filter out the lymph and store lymphocytes
An increase in the number of bad white blood cells
A protein in the body that is designed to fight disease; antibodies are brought on by the presence of certain antigens in the system.