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 to the bloodstream. As this occurs, the fluid (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 node locations
- Below the jaw – submandibular
- Cervical – neck
- Armpits – axillary
- Chest – tracheobronchial
- Mesentery/intestines – mesenteric
- Pelvis – iliac
- Groin – inguinal
- Rear leg, close to the knee – popliteal
When an infection occurs, the lymph nodes closest to the site of infection become swollen (lymphadenopathy). Swelling occurs as a result of an increase in the number of immune cells.
The three leading causes of swollen lymph nodes:
- Infection – Can include bacterial, viral, fungal and protozoal infection
- Cancer – Cancer of the blood (leukemia), lymph nodes (lymphoma) or cancer of a nearby organ
- Immune-mediated – Allergies, eosinophilic reactions
Swollen lymph which may be painful to the touch. Other symptoms will depend 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 which may have originated there (primary) or originated from another location and been transported to the lymph nodes (secondary).
If you notice your cat has swollen lymph nodes, it is important to see a veterinarian to determine the cause. The age of the patient can narrow down probable causes. Infections are more common in young cats and cancer in old cats.
The veterinarian will perform a complete physical examination and evaluate the swollen gland(s). The number of affected glands, size and location, can give a clue.
- Has your cat had a recent infection?
- What other symptoms (if any) does your cat have?
- Do the symptoms come and go?
- Have there been any changes to your cat’s weight?
Some veterinarians may recommend a wait and see approach if they suspect an infection. Once it has run its course, 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, it can point to a more serious underlying problem, namely cancer.
- Fine needle aspiration – The veterinarian inserts a fine needle into the lymph node, to remove a sample of tissue which is evaluated by a pathologist.
- Lymph node biopsy – Removal of the lymph node, which is evaluated by a pathologist.
- X-ray and/or ultrasound – To evaluate the lymph nodes and look for possible tumours.
The goal of treatment is to find and treat the underlying cause, which may include:
Bacterial infection: Antibiotic therapy which may be oral or injectable. The veterinarian may perform a culture and sensitivity to determine the most suitable antibiotic.
Fungal infection: Antibiotics or antifungals along with supportive care.
Viral infection: Antivirals (where appropriate) as well as supportive care such as fluid therapy and nutritional support while the cat’s immune system fights off the virus.
Immune-mediated: Immune suppressants to dampen down the immune response, if the cause of allergies is determined, then the best course of treatment is to avoid the trigger.
Cancer: Surgery to remove the tumour where possible along with chemotherapy or radiotherapy as a follow-up, or a stand-alone treatment for cancers where removal is not possible. Affected lymph nodes will also be removed at this time. If cancer has spread from another location such as the lungs (metastasised), the prognosis is poor.