Lymphadenitis in Dogs
Inflammation of the lymph nodes, a condition known as lymphadenitis, is characterized by inflammation of the nodes due to an active migration of white blood cells. There are different types of white blood cells that can cause this: neutrophils, the most abundant type of white blood cells in the body; macrophages, the cells that engulf and digest cellular debris and pathogens in the bloodstream; or eosinophils, the white blood cells of the immune system.
Because of the filtration functions of the lymph nodes, they are likely to be exposed to infectious agents. Lymphadenitis is usually the result of an infectious agent gaining access to a lymph node and establishing an infection, with a resulting response by the immune system to fight the infection with increased white blood cell production. Such infectious agents include fungi and mycobacteria (pathogens known to cause serious diseases in mammals) .
There is no known genetic basis to lymphadenitis, except for rare cases of immunodeficiency; e.g., the familial susceptibility of certain basset hounds to mycobacteriosis (mycobacteria are widespread in the natural world, particularly in aquatic environments), of which lymphadenitis is a frequent manifestation. However, newborn puppies may have a higher rate of occurrence than older dogs, since their still undeveloped immune systems make them more susceptible to infection.
Symptoms and Types
Lymphadenitis seldom causes lymph node enlargement that is severe enough for someone unfamiliar with veterinary medicine to observe. Your dog's doctor, however, will be able to locate the firm nodes through palpation, which is often painful for the animal. The dog may also have a fever, suffer from inappetance (anorexia), or display other systemic signs of infection. Bacterial infections, in particular, may develop abscesses within the nodes, which may open to the exterior and present as draining tracts. Other complications will depend on the location of the infection and whether it is affecting surrounding organs.
- Most pathogenic species have occasionally been reported
- Most likely agents are Pasteurella, Bacteroides, and Fusobacterium spp
- A few, such as Yersinia pestis (bubonic plague), and Francisella tularensis (tularemia), have a particular affinity for lymph nodes and are especially likely to be manifest as lymphadenitis
- Bartonella vinsonii infection may cause granulomatous (nodular) lymphadenitis in dogs
- Infections commonly include lymphadenitis as one manifestation of a systemic disease
- Likely organisms include Blastomyces, Cryptococcus, Histoplasma, Coccidiodes, Sporothrix
- Other fungal agents have occasionally been reported
- Many viral infections are implicated in lymphoid hyperplasia
- Mesenteric (wall of the abdomen) lymph nodes are most commonly affected
- Protozoa - dogs with toxoplasmosis and leishmaniasis frequently have lymphadenitis although it is unlikely to be the most obvious clinical finding
- Noninfectious (e.g., associated with pulmonary or systemic eosinophilic disease) cause is usually unknown
- Dogs with compromised immune function are susceptible to infection and, therefore, to lymphadenitis
You will need to provide a thorough history of your dog's health leading up to the onset of symptoms. Your veterinarian will need to ascertain that a palpable or visible mass is actually a lymph node and not a tumor or another kind of inflammation. Also, it may be difficult to distinguish on the basis of clinical findings from other causes of lymph gland enlargement, or a proliferation of cells in the lymph nodes for some other reason, such as cancer.
To be certain of making the correct diagnosis, your veterinarian will order a complete blood count and urinalysis to look for evidence of bacterial and fungal diseases. If the swollen nodes are in the chest and abdomen, diagnostic testing will include X-ray and ultrasound imaging to make a determination. A fine-needle aspiration of the lymph nodes themselves may also be performed to gather sample of the fluid and tissue that is within the nodes, so that the exact internal composition of the lymph nodes can be analyzed.