The lymphatic system is a series of tubular structures (similar to veins) known as lymphatic ducts which pick up excess fluid leaked from the blood capillaries, returning it back to the bloodstream, as this occurs, the fluid (known as lymph) passes through the lymph nodes (bean-shaped organs), where bacteria, viruses, fungi, cancer cells and trapped and destroyed by white blood cells known as lymphocytes.
Lymph nodes are found in various locations throughout the body, including the throat (mandibular), armpits (axillary), chest (tracheobronchial), mesentery (mesenteric), pelvis (iliac), groin (inguinal), rear leg, close to the knee (popliteal). Lymph nodes are sometimes referred to as "glands", this is incorrect, they are not glands.
When an infection occurs, the lymph nodes closest to the site of infection become swollen. This is known as 'lymphadenopathy'. Swelling occurs as a result of an increase in the number of immune cells.
What causes swollen lymph nodes?
There are four main causes of swollen lymph nodes:
- Infection (bacterial, viral, fungal, protozoal).
What are the signs of swollen lymph nodes?
Obviously, swollen lymph nodes are the main symptom, these may be painful to the touch. Other symptoms may be present depending on the underlying cause. For example, if your cat has a dental abscess, the lymph nodes in the throat may become enlarged. Common signs of infection include loss of appetite, fever, lethargy.
Cancer cells can also be found in the lymph nodes. They may have originated in the lymph nodes (primary) or cancer cells which have originated from another location and been transported to the lymph nodes (secondary).
How to check for swollen lymph nodes:
Some lymph nodes are located deep within the body, others lie close to the skin. The easiest locations to check for swollen lymph nodes in cats is the following:
- Where the jaw meets the neck (submandibular).
- Where the front leg meets the shoulder (prescapular).
- In the armpit area behind the front legs (axillary).
- In the rear leg, opposite the knee (popliteal).
Locating the lymph nodes can be quite tricky, and is best attempted by your veterinarian.
How are swollen lymph nodes diagnosed and treated?
If you notice your cat has swollen lymph nodes, it is important to see a veterinarian to determine the cause.
Treatment is aimed at addressing the underlying condition, for example, antibiotics to treat a bacterial infection, or anti-fungal medication to treat fungal infections, removal of the allergen (if possible). Many viral infections require supportive care such as hospitalisation and IV fluids while your cat fights off the infection.
Sometimes infection may be present without symptoms, if your veterinarian suspects your cat has an infection, he may perform the following tests:
Complete blood count, biochemical profile, and urinalysis. These tests can check for signs of infection as well as measure your cat's overall health.
Once an infection has run its course, or an allergy treated, the swollen lymph nodes will eventually shrink back to their original size. This can take a few weeks to occur. If however, they remain swollen, or if no infection has occurred, it can indicate a more serious underlying problem, namely cancer. If your cat has swollen lymph nodes, and infection has been ruled out, your veterinarian will need to run some diagnostic tests to look for cancer. This may include:
- Lymph node biopsy - A sample is removed for microscopic evaluation.
- X-ray or ultrasound - To evaluate the lymph nodes and look for possible tumours.
If cancer is diagnosed, then the most common treatment options include surgical removal (where possible), and/or chemotherapy and radiotherapy. Affected lymph nodes will also be removed at this time. If the cancer has spread from another location (metastasized), the prognosis is usually guarded.