Page 405 - Problem-Based Feline Medicine

20 – THE CAT WITH ENLARGED LYMPH NODES 397

characterized by a clinically enlarged node but nor- Lymph nodes may be painful, warm and soft with
mal cellular composition on biopsy; the latter is bacterial and fungal lymphadenitis. Lymph nodes are
characterized by a mild to marked increase of painless, firm and at body temperature with most other
plasma cells, with or without a mild increase of diseases.
immature lymphocytes and/or macrophages. These
Lymph nodes may be fixed (instead of mobile) with
two patterns have the same etiologies, will not be
lymphadenitis, metastatic neoplasia and lymphoma
distinguished here, and will be referred to as
with extracapsular invasion.
“hyperplasia”.
● Based on lymph node histology, patterns of lymph Lethargy, inappetence, weight loss and fever may be
node hyperplasia may vary, e.g. as follicular cen- present, especially with generalized lymphadenopathy.
ter expansion (B-cells), paracortical expansion
Local or regional enlargement is usually due to a disorder
(T-cells), combined B- and T-cell hyperplasia, and
in the area drained by the node(s).
sinusoidal cell hyperplasia (macrophages). In
most disorders lymph node architecture is pre-
served.
● Hyperplasia is generally a non-specific finding.
WHERE?
● Some tendencies for specific cytologic and histologic
patterns occur with certain diseases, e.g. increased The focus of this chapter is peripheral lymph-
numbers of eosinophils in parasitic skin diseases. adenopathy (e.g. mandibular, prescapular, axillary,
Communicating with the pathologist may assist the inguinal and popliteal nodes). There may be accompa-
clinician in determining etiology. nying internal lymphadenopathy (e.g. hilar and mesen-
● Hyperplasia may be the initial finding before the teric nodes).
development of detectable neoplasia or lym- ● Inguinal fat should not be mistaken for enlarged
phadenitis. inguinal nodes and contracted muscles of the caudal
● Hyperplastic nodes without a diagnosis should be aspects of the hindlimb should not be mistaken for
cultured for bacteria and fungi. popliteal nodes.
Neoplastic lymphadenopathy is characterized by pro- Diseases causing primarily internal lymphadenopathy
liferation or invasion of malignant cells. are discussed in The Dyspneic or Tachypneic Cat, The
● Lymphoma and lymphoid leukemia are due to pro- Cat With Chronic Diarrhea and The Thin Inappetent
liferation and invasion of malignant lymphocytes. Cat.
● On histology, lymphoid neoplasia typically dis-
rupts lymph node architecture and demonstrates
a uniform cell-type and chromatin pattern.
● Other hematopoietic tumors and solid tumors WHAT?
may metastasize to local, regional or distant nodes.
The most common causes of generalized lymph-
Lymphadenitis is characterized by a cellular infiltrate adenopathy are chronic generalized skin diseases (der-
of neutrophils (suppurative) macrophages (pyogranulo- matopathic lymphadenopathy), FeLV/FIV infections and
matous), or eosinophils (eosinophilic), focal necrosis or lymphoma.
abscessation. It usually results from an extension of an ● The most common causes of marked generalized
inflammatory process into the node. lymphadenopathy are chronic flea allergy dermati-
● Severe, peracute infectious lymphadenitis may tis, lymphoma, idiopathic atypical hyperplasia and
cause hemorrhage and necrosis with destruction of acute FIV infection.
architecture, minimal inflammatory infiltrate, and
The most common causes of local and regional lymph-
nodal and perinodal edema.
adenopathy are bacterial and fungal infections in the
Lymphadenopathy may be mild to marked with any cause. area drained by the node(s).
● Lymphadenopathy tends to be more prominent in ● The most common cause of marked solitary lymph-
younger animals compared to older animals. adenopathy is abscessation.