As the lymphatic system plays a crucial role in preserving the integrity of the immune system and as we have looked, in previous articles, at what can happen when the immune system malfunctions, it seems a natural progression to examine what can occur when the lymphatic system is attacked.
Lymphatic cancer, or lymphoma, emanates from lymphocytes; the lymphatic cells or white blood cells and these are not confined to one area of the body but travel through the dog's system. From this it can be readily appreciated that such a cancer is potentially very serious and can cause deterioration in the patient very rapidly.
The lymph glands are situated in several areas of the body. Some nodes are superficial and can be felt whilst others lie deeper in the body's system. Those nodes near the surface are to be found in the armpit (axillary), the groin (inguinal) in the front of the shoulder (prescapular), beneath the jaw (submandibular) and behind the knee (popliteal).
There is a great variation in the aggressiveness of lymphatic cancer. Sometimes acute severe illness develops very quickly and there is rapidly advancing deterioration. Sometimes the disease takes a more chronic form with slower progression and more time to arrange efficacious treatment regimens.
Wherever there is lymphoid tissue there is the chance for lymphoma to develop. Organs that can be targeted are the liver and spleen, whilst the bone marrow is also not uncommonly involved.
The most usual form of the disease is multicentric lymphoma and the lymph nodes are the most usual site. The glands are enlarged with a firm swelling detectable upon palpation but the swelling is painless. However, there can be cutaneous, mediastinal and alimentary forms of the disease.
General symptoms of illness such as lack of appetite, excessive lethargy, loss of body weight and polydipsia and polyuria (excessive drinking and urination) are often present in cases of lymphoma. These symptoms might, initially, be ascribed to diseases of a less serious nature.
In cutaneous cases, the skin alters its appearance, becoming inflamed and irritated. Unless diagnosed and treated this can lead to ulceration and consequent infection. Sometimes the symptoms give rise to an incorrect diagnosis of general allergy or dermatitis.
Alimentary lymphoma will, as expected, give rise to symptoms of digestive disorder such as diarrhoea and/or vomiting. Any lymphatic tumour that affects the chest (mediastinal) will compromise effective respiration, either because of the tumour in the chest itself or due to an accumulation of fluid in the space between lungs and chest cavity (pleural effusion). One of my dear old Jacob sheep had a mediastinal tumour that gave rise to such distressing respiratory malfunction that euthanasia shortly became necessary.
When arriving at a diagnosis of lymphoma, tests such as fine needle aspiration to obtain a cell sample from a superficial node might be carried out. This is generally not an invasive procedure so, although sedation might be required, a general anaesthetic is not. However, if it is decided to excise the lump for biopsy, anaesthesia will be used.
Also our old friends, blood tests, blood chemistry profiles, urine tests and X rays can be of use in determining both the rate of spread and the success of treatment for this condition. Blood tests can be of particular value. Anaemia will probably be present if very low levels of lymphocytes are in the blood (lymphopenia). Elevated levels of neutrophils (which are certain types of white blood cells) in the blood is a suspicious finding. Another type of white blood cell, known as a monocyte, might show elevated levels in a dog with lymphatic cancer. Blood clotting cells (platelets) could be much lower in number than normal. This condition is known as thrombocytopenia. We have come across it in the article on haemolytic anaemia.
If cancer of the bone marrow, probably diagnosed as acute lymphoblastic leukaemia, is suspected, then samples of marrow can confirm this. A short acting general anaesthetic would be administered prior to such a procedure.
As with the immune mediated diseases we have looked at, some breeds do appear to be more vulnerable to developing lymphatic cancer. These include the Basset Hound, the Aberdeen terrier (known more usually as the Scottie), Golden Retriever and certain brachycephalic breeds (those with very short noses) such as the Bulldog and the Boxer.
There appears to be no gender based predisposition and the disease can occur at any age although, as with human patients, increasing age seems to bring slightly increased risk.
Chemotherapy is generally indicated once a firm diagnosis is achieved. This can be encouragingly effective in some animals where the spread of the disease is not too advanced and the patient is otherwise in good health. As in humans, following treatment there can be periods of remission from the disease, and the individually tailored requirements of drug combinations and timescales for administration of them can lead to a reasonable or good quality of life for some dogs.
It must be appreciated though that it is rarely if ever possible to cure the disease. The aim should be to enable the animal to enjoy a fair quality of life for a while. Most dogs treated for lymphoma live for about a year. Sadly, the cancer will probably return after a period of remission and treatment will probably decrease in effectiveness as the cancer becomes resistant to the medication. As in humans, chemotherapy will lower the body's defences against infections so keep a close eye on your dog during treatment and familiarise yourself with what to expect during it.