How Lymphoma is Diagnosed in Dogs
Lymphoma typically causes very general clinical signs in domestic dogs, which can mimic symptoms of viral or bacterial infection and a number of other diseases. However, canine lymphoma is not particularly difficult to diagnose, as long as the dog’s owner is able to proceed with and complete the diagnostic process.
The initial data base for a dog presenting with nonspecific symptoms of illness first involves a thorough physical examination and a complete history. Routine blood work and a urinalysis are also typically part of an initial work-up. The complete blood count may disclose anemia and elevated immature white blood cells, which are suggestive of lymphoma. The serum chemistry panel may show elevated blood calcium levels, abnormal liver enzyme levels and kidney abnormalities. The most reliable way to diagnose lymphoma in dogs is to take samples from enlarged lymph nodes and/or other affected organs. Usually, the attending veterinarian will recommend a fine needle aspirate (FNA) of one or more enlarged peripheral lymph nodes. This simple procedure involves inserting a small needle into the suspicious lymph nodes and withdrawing fluid and cells through an attached syringe. The sample is then expressed onto a glass slide and examined under a microscope to identify any cellular abnormalities. This process, called cytology, can in many cases be definitively diagnostic of lymphoma.
If FNA and cytology are inconclusive, and often even if they point strongly to lymphoma, biopsies of one or more enlarged lymph nodes normally will be taken. A biopsy involves surgically removing pieces of tissue, rather than only sampling cells, from the questionable organs or areas. Biopsies typically require heavy sedation, and sometimes general anesthesia. Biopsy samples are then submitted to a pathology laboratory, where they are processed and evaluated for abnormalities by a technique called histopathology. Biopsy and histopathologic tissue evaluation are the gold standard for diagnosing canine lymphoma. Suspicious lymph nodes can also be entirely removed surgically, for more thorough histopathologic examination.
Bone marrow aspiration or biopsy can be helpful in assessing whether lymphoma has spread widely throughout the dog’s body. Chest and abdominal radiographs (X-rays), together with ultrasound examinations, are especially helpful in identifying abnormally enlarged lymph nodes, affected organs (especially liver and/or spleen) and isolated masses. A cerebrospinal fluid (CSF) tap can be useful if the dog is showing neurological signs. A genetic screening test for canine lymphoma has recently become commercially available and apparently is based on genetic markers that are identifiable from a blood sample. Other advanced diagnostic tests for lymphoma include immunocytochemistry, immunohistochemistry, flow cytometry and PCR (polymerase chain reaction) amplification of chromosome sequences.
Even though lymphoma usually causes nonspecific symptoms, it is fairly easy for veterinarians to diagnose if there are no significant financial or other constraints on the part of the dog’s owner.