Clinical Conditions Affecting the Lymphatic System
• Splenomegaly is enlargement of the spleen and can be either localised or generalised. Localised splenomegaly can be an abscess, neoplasia, hyperplasia or a haematoma. Generalised splenomegaly may be neoplastic, e.g.
leukaemia; inflammatory, e.g. hepatitis; hyperplastic, e.g. bacterial endocarditis; or congestive, e.g. splenic torsion.• Lymphosarcoma (lymphoma) is common in dogs and cats and can involve the liver, lymph nodes, bone marrow, the spleen and commonly in the intestine. Cats that are positive for leukaemia (feline leukaemia virus [FeLV]) are more likely to develop lymphosarcoma. Certain dog breeds are more susceptible to lymphosarcoma, e.g. Boxers, Golden Retrievers and Basset Hounds. The clinical signs include enlargement of lymph nodes, loss of appetite, loss of weight, vomiting, diarrhoea and lethargy. Lymphosarcoma can affect any organ containing lymphocytes, e.g. kidneys, spinal cord and skin. The disease results in the proliferation of malignant lymphocytes.
A vaccine against FeLV is available for cats. Chemotherapy is the best treatment but the disease is often fatal.
• Lymphadenopathy is the term generally used to describe disease affecting the lymph nodes. Reactive hyperplasia of lymph nodes is the enlargement of lymph nodes in response to the pathology of the tissues filtered by those lymph nodes. There are many substances that are carried to the lymph nodes; some are harmless and are simply phagocytosed, while others cause an immune reaction resulting in swelling of the affected lymph nodes. Examples of causative agents are bacteria, viruses, chemicals and neoplastic cells.
• Feline leukaemia virus only affects cats. It is caused by a transmissible retrovirus and is invariably fatal. The clinical signs are anaemia, weight loss, fatigue, oral disease and enlargement of lymph nodes. The disease is highly contagious and is transmitted in saliva, urine, faeces and nasal secretions. An effective vaccine is available and is recommended.
• Haemangiosarcoma in dogs. This serious condition is invariably fatal unless emergency surgery is carried out. One survey concluded that one in five Golden Retrievers will suffer this neoplastic disease. It is the endothelial cells lining the blood vessels of the spleen that become neoplastic. Apart from a swollen abdomen and anaemia there are few clinical signs until the spleen ruptures. A weak pulse, pale mucous membranes, rapid heart rate and panting may be apparent. Haemangiomas can occur elsewhere, e.g. liver or skin, but are most frequent in the spleen. Emergency surgery, usually removal of the spleen and a blood transfusion followed by chemotherapy, gives the best chance of survival.