Rule out for enlarged peripheral lymph nodes, infections, hyperplasia from inflammation, or neoplasia, hyperplasia from inflammation, or neoplasia.
The veterinarian treated the otitis externa with Mometomax (gentamicin sulfate, mometasone furoate monohydrate and clotrimazole) and performed a CBC, chemistry profile, 4 DX and urinalysis and aspirated the mandibular and prescapular lymph nodes.
Chemistry showed a mildly elevated GGT at 21 (range 0-13). Urinalysis showed a specific gravity of 1.042 with an inactive sediment. A peripheral lymphocytosis (8525) was noted on the CBC with the pathologist’s comment that the lymphocytes were small-to-intermediate in size and well-differentiated in appearance. The balance of the CBC was WNL. The 4 Dx was negative.
Cytology of the lymph nodes showed a population of small to intermediate lymphocytes with cytoplasmic pseudopods known as “hand-mirror” morphology with a diagnosis of a possible small cell lymphoma/leukemia (see photo). Murphy was then referred to the Tufts Harrington Oncology Service for further evaluation.
On exam, the peripheral lymphadenopathy was confirmed and a CBC was repeated with results similar to what was found at Murphy’s primary care veterinarian. After discussion with the owner, it was recommended that samples of the affected lymph nodes be taken for flow cytometry. Flow cytometry utilizes specific immunohistochemical markers to better characterize lymphoid malignancies. These markers can be very important for both prognosis and to determine recommended treatment options.
Flow cytometry requires a suspension of live cells in the sample for the flow cytometry to be diagnostic. The cells are passed through an electronic detection apparatus that sorts the cells based on size and various markers. Flow cytometry can be performed on whole blood in EDTA for leukemic samples and on a lymph node aspirates when multiple aspirate samples are placed in isotonic saline with 10% canine serum. Samples were obtained of Murphy’s lymph nodes and were positive CD3+ and CD 5+ with loss of CD 45. These results were diagnostic for a T zone lymphoma, a type of indolent T cell lymphoma.
Lymphoma is the most common hematopoietic malignancy in the dog. It is estimated that as many as 20-25% of all lymphomas diagnosed in dogs are indolent in nature and the incidence may be even higher for leukemias. Indolent malignancies are characterized by slow growth and a prolonged clinical history and it is important to recognize this difference in clinical patients, as it can carry a substantially different prognosis.
T zone lymphoma tends to carry a guarded to good prognosis. Monitoring is recommended with periodic complete blood counts and physical exams. Most patients diagnosed with an indolent lymphoid malignancy are nine to 12 years of age with no apparent sex predilection. Not all indolent lymphomas require treatment and some may be best managed with close monitoring and may not need cytotoxic chemotherapies. Median remission time for T zone lymphoma is reported as >1,000 days, with most pets not succumbing to their disease.
The main types of indolent lymphoid neoplasias are broken down by phenotype through immunohistochemistry and descriptive appearance on histopathology (see chart below). Use of flow cytometry or immunohistochemistry is vital in differentiating these types of lymphoma from their more aggressive counterparts.
A consultation with a veterinary oncologist and discussion with the owners of the risks and benefits of each specific case is recommended when a patient is diagnosed with an indolent form of lymphoma.
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