Comprehensive laboratory evaluation of cats with unexplained abdominal lymphadenopathy should include complete blood count,
serum chemistry profile, urinalysis, tests for feline leukemia virus antigen and feline immunodeficiency virus antibody and
complete fecal parasitological examination.
Additional serologic tests, based on a cat's signalment and clinical signs, include IgM and IgG titers for Toxoplasma gondii, baseline feline coronavirus antibody titer (to exclude infection), and urine antigen titers for Histoplasma capsulatum when no organisms have been identified.
Additional polymerase chain-reaction (PCR) testing on blood, lymph-node aspirates, body-cavity effusion and feces may be indicated
in coronavirus-seropositive cats in which the suspicion of FIP is high. Serologic evaluation for Ehrlichia canis-like organisms may be performed when more common causes of systemic illness and visceral lymphadenomegaly have been excluded.
Serum cobalamin and serum folate levels, in combination with serum trypsin-like immunoreactivity levels, should be performed
when concurrent weight loss and gastrointestinal signs (including thickened intestinal loops) are noted. In a recent study,
78 percent of cats with low-grade lymphocytic lymphoma were found to have decreased cobalamin levels; mesenteric lymph-node
involvement was noted in six of 41 affected cats.
Ultrasound evaluation is considered more sensitive than survey radiography for detecting the presence of abdominal lymphadenomegaly;
however, it is not sensitive for the identification of the underlying cause of the lesions. Fine-needle aspirates or biopsies
of lymph nodes are needed to clarify the ultrasonographic changes.
Abdominal lymph nodes are classified as visceral or parietal, according to the anatomic area that they drain. Visceral lymph
nodes include the jejunal nodes (also known as the cranial mesenteric nodes) and the right colic lymph nodes, both of which
are often enlarged in inflammatory bowel disease or alimentary lymphoma. Ultra-sonographic evidence of abdominal lymphadenopathy
has been found in up to 50 percent of cats with alimentary lymphoma, with intestinal masses being identified sonographically
in about 40 percent of affected cats.
Ultrasonographic parameters that are useful to distinguish normal from abnormal lymph nodes include nodal size, shape, margin
characteristics, echogenicity, echotexture, acoustic transmission, the presence of vascular flow and its distribution and
the measurement of vascular flow indices.
Doppler evaluation of the abdominal lymph nodes of cats with alimentary lymphoma may show aberrant blood vessels entering
the nodes in abnormal locations, in comparison to normal lymph nodes in which the hilus is the usual point of entry. On a
practical basis, the parameters that provide the best predictability are the size and shape of the lymph node(s), the distribution
of vessels within the node and the pulsatility index that reflects vascular resistance within the node.
Small lymphocytes comprise 75 percent to 90 percent of the lymphocyte population obtained from normal lymph nodes, with medium-sized
lympho-cytes contributing 5 percent to 15 percent, and lymphoblasts 5 percent. Hyperplastic lymph nodes have the same respective
lymphocyte counts as normal lymph nodes; however, nodal size is increased.
Reactive lymphadenopathy is characterized by a small to moderate increase in the numbers of prolymphocytes, lympho-blasts
and plasma cells. Both of these cytologic findings are considered to be the result of lymphoid proliferation in response to
Lymphadenitis is characterized by an increase in inflammatory cells, including neutrophils, macrophages and eosinophils. The
response is classified as primary if the lymph node is infected and secondary if the lymph node is not infected but is draining
an infected lesion in its region.
Lymphoblasts usually comprise at least 50 percent of the cell population in lymph nodes from cats with lymphoblastic lymphoma.
Mesenteric lymph-node aspirates from cats with low-grade lymphocytic lymphoma may yield a homogeneous population of small
lymphocytes, in the absence of normal numbers of precursor cells.
Biopsy and histopathologic examination may be necessary to confirm the diagnosis of lymphoma. PCR testing to detect the presence
of a clonal lympho-cyte population also may be useful to confirm the cytologic or histo-pathologic findings.
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: