Feline Lymphadenopathy Study Guide

Overview and Clinical Importance

Lymphadenopathy refers to enlargement of lymph nodes, which can be solitary, regional, or generalized. In feline patients, lymphadenopathy is an important clinical finding that signals underlying disease processes ranging from reactive hyperplasia to neoplasia. Unlike dogs, where multicentric lymphoma commonly presents with generalized peripheral lymphadenopathy, cats more often develop

alimentary lymphoma affecting the gastrointestinal tract. Understanding the differential diagnoses and diagnostic approach to feline lymphadenopathy is essential for NAVLE success.

Feline Lymph Node Anatomy

Palpable Peripheral Lymph Nodes

The following peripheral lymph nodes are routinely palpable in healthy cats and should be evaluated during every physical examination:

Abdominal Lymph Nodes

Abdominal lymph nodes cannot be palpated unless markedly enlarged. Ultrasound is essential for evaluation. Key abdominal lymph nodes include:

Classification of Lymphadenopathy

Lymphadenopathy is classified into three main categories based on underlying pathophysiology:

Differential Diagnosis

Infectious Causes

Retroviral Infections (FeLV and FIV)

Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV) are major causes of generalized lymphadenopathy in cats. FeLV is historically linked to lymphoma development, particularly mediastinal lymphoma in young cats. FIV causes immunosuppression leading to secondary infections and lymphadenopathy.

Key clinical features: Generalized lymphadenopathy, weight loss, anemia, immunosuppression, secondary infections

Feline Infectious Peritonitis (FIP)

FIP is a coronavirus-induced disease characterized by pyogranulomatous inflammation. Abdominal lymphadenopathy is a prominent feature, especially in the non-effusive (dry) form. Approximately 16% of cats with FIP present with isolated intramural intestinal masses and regional lymphadenomegaly, which can mimic neoplasia.

Key clinical features: Young cats (often less than 2 years), fever unresponsive to antibiotics, hyperglobulinemia, mesenteric lymphadenopathy, ocular or neurologic signs

Systemic Mycoses

Histoplasmosis: Caused by Histoplasma capsulatum. Endemic to Mississippi and Ohio River valleys in the US. Causes peripheral and abdominal lymphadenopathy with respiratory signs, weight loss, fever, anemia, and hepatosplenomegaly. Organisms may be seen within macrophages on cytology.

Sporotrichosis: Caused by Sporothrix species. Has significant zoonotic potential from cat scratches. Presents with nodular, ulcerated skin lesions and regional lymphadenopathy. Endemic in South America and increasingly reported in the US.

Cryptococcosis: Upper respiratory and CNS involvement common. Can cause submandibular lymphadenopathy with nasal disease.

Other Infectious Causes

Neoplastic Causes

Lymphoma

Lymphoma is the most common hematopoietic neoplasm in cats, accounting for approximately one-third of all feline tumors. Unlike dogs, alimentary (gastrointestinal) lymphoma is the most common form in cats, followed by mediastinal, multicentric, and extranodal forms.

Metastatic Neoplasia

Regional lymph nodes should be evaluated when staging any malignancy. Common tumors that metastasize to lymph nodes include:

• Squamous cell carcinoma (SCC): Oral and cutaneous forms metastasize to regional lymph nodes
• Mammary carcinoma: Metastasizes to inguinal and axillary lymph nodes
• Mast cell tumor: Can metastasize to regional nodes; cytology shows characteristic granulated round cells
• Melanoma: Oral melanoma metastasizes to mandibular and retropharyngeal nodes

Diagnostic Approach

Initial Assessment

History: Duration of lymphadenopathy, associated clinical signs (weight loss, lethargy, GI signs), vaccination history, geographic location, diet (raw food increases risk of Listeria, Salmonella), outdoor access, FeLV/FIV status

Physical examination: Palpate all peripheral lymph nodes systematically. Assess size, consistency, mobility, symmetry, and pain on palpation. Evaluate for concurrent findings (fever, skin lesions, ocular changes, abdominal masses)

Laboratory Evaluation

Minimum Database

• CBC: May reveal cytopenias (bone marrow involvement), eosinophilia (parasitic, allergic, mast cell tumor), or circulating neoplastic cells
• Serum chemistry: Hyperglobulinemia suggests FIP or chronic inflammation; hypercalcemia is rare in feline lymphoma but can occur
• FeLV/FIV testing: Essential in all cats with lymphadenopathy
• Urinalysis: Baseline renal function; Histoplasma antigen testing on urine

Fine Needle Aspirate Cytology

FNA cytology is the first-line diagnostic test for lymphadenopathy. It is quick, inexpensive, minimally invasive, and often diagnostic.

Technique: Use a 22-gauge needle and 6-12 mL syringe. Apply slight negative pressure and redirect in fan-like pattern. Avoid pumping which damages fragile lymphoid cells. Use roll preparation to minimize cell lysis.

Diagnostic Imaging

Abdominal Ultrasound

Ultrasound is the preferred modality for evaluating abdominal lymph nodes and is more sensitive than radiography. Key findings include:

• Size: Enlarged nodes appear rounded rather than elongated
• Echogenicity: Most abnormal nodes are hypoechoic; reactive nodes often surrounded by hyperechoic fat
• Architecture: Loss of normal elongated shape, heterogeneous echotexture
• Associated findings: Intestinal thickening (IBD, lymphoma), effusion (FIP, carcinomatosis)

Key point: Mesenteric lymphadenopathy is present in 33-50% of cats with alimentary lymphoma and correlates with IBD severity. However, ultrasound cannot reliably differentiate IBD from low-grade lymphoma.

Additional Diagnostics

Treatment

Treatment by Etiology

Chemotherapy for Lymphoma