Lymphoma or lymphosarcoma is a tumor of white blood cells. It is a malignant cancer, and it may affect one or more parts of the lymphatic system. Lymphoma may occur as a solid tumor associated with the lymph nodes, the intestines, kidneys, liver, spleen, thymus or other parts of the body. It may also develop as a circulating form that is confined largely to the bone marrow and blood stream. Lymphoma is one of the most common cancers seen in dogs, and has been treated with chemotherapy protocols for a number of years.
What Are Common Diseases of the Lymphatic System?
Due to the distribution and complexity of the lymphatic system, many disorders may affect all or some part of it. The most common disorders seen in dogs include the following:
Lymphadenopathy is enlargement of the lymph nodes. It may represent lymphosarcoma, but may also develop for other reasons. Lymph nodes may enlarge when they are reacting to foreign substances or infection. They become larger as white blood cells proliferate within the nodes. Such reactions may also occur following vaccination or with any chronic inflammation within the body.
Lymphadenitis is inflammation of the lymph nodes. It may involve one or several lymph nodes, depending upon the cause. Common causes include wounds, skin infections, infections within the soft tissues of the body, nonlymphatic tumors, and areas of active healing.
Chylothorax is the accumulation of chyle in the chest cavity from rupture, obstruction, or abnormal development of the thoracic duct. It may develop secondary to heart disease, tumors of the thorax, diaphragmatic hernias, trauma, fungal infections, heartworm disease, and for unknown reasons. It is more common in Afghan hounds and Shiba Inu dogs than in other breeds.
Lymphangitis is an inflammation of the lymph vessel. It often arises from trauma, foreign bodies, and infections. It may occur at the same time as lymphadenitis.
Lymphangiectasia is an obstructive (blockage) disorder that causes dilation of the lymph vessels, particularly in the intestinal tract.
Lymphedema is an accumulation of lymph in the soft tissues of one or more of the limbs. Congenital forms occur in some dogs (e.g. poodles, Labrador retriever, Great Dane) due to deformities in either the lymphatic channels or the lymph nodes themselves. Acquired forms may occur with blockage or destruction of lymph vessels from trauma, surgery, inflammation, infection, tumors, or radiation therapy. In some cases the soft tissue swells so much that the limb may be painful or dysfunctional.
What Types of Diagnostic Tests Are Used to Evaluate the Lymphatic System?
Several tests are particularly helpful in evaluating the lymphatic system. Depending on the part or parts of the lymphatic system involved, a combination of tests may be recommended by your veterinarian. A complete blood count (CBC), biochemical profile, and urinalysis are recommended to help evaluate organ functions, to detect evidence of infection or inflammation throughout the body, and to assess the types of white blood cells present in the circulation.
Blood tests that screen for infectious diseases such as the systemic fungal infections, the tick borne diseases and certain bacterial infections (e.g. brucellosis) may be of benefit in cases with lymphadenopathy or abnormal circulating numbers of white blood cells.
Chest and abdominal X-rays and ultrasonography are useful to evaluate abdominal organs including the spleen, intestines, liver, kidney and abdominal lymph nodes. They also detect the presence of fluid in the chest, such as in the case of chylothorax.
A bone marrow aspirate or biopsy is performed for diseases involving the bone marrow.
Fine-needle aspiration of enlarged lymph nodes or other abnormal tissues, followed by cytology (microscopic analysis of the cells) may be diagnostic for lymphoma, reactive lymphadenopathy or lymphadenitis. In some cases an actual biopsy (piece of tissue) is needed for diagnosis.
Analysis of fluid retrieved from the chest can confirm the presence of chylothorax.
Bacterial cultures may be submitted if bacterial infections are suspected.