Clonal T Cell Proliferation Induced by Acute Anaplasmosis in a Dog

Area of Science:

• Veterinary Internal Medicine
• Canine Infectious Diseases
• Clinical Pathology

Background:

• Tick-borne diseases present diagnostic challenges in dogs.
• Lymphoma and infectious causes can present with similar clinical signs and cytological findings.
• Accurate diagnosis is crucial for effective treatment and patient outcomes.

Observation:

• A Golden Retriever presented with hindlimb lameness, lethargy, and pyrexia post-tick exposure.
• Initial diagnostics revealed thrombocytopenia, lymphopenia, and lymphadenopathy.
• Joint fluid analysis suggested lymphoma, with flow cytometry identifying aberrant CD4+ T cells and PARR confirming T-cell clonality.

Findings:

• Peripheral blood PCR confirmed Anaplasma phagocytophilum infection.
• The patient's clinical signs and laboratory abnormalities resolved following doxycycline treatment.
• Post-treatment joint fluid analysis normalized, ruling out lymphoma.

Implications:

• Anaplasma phagocytophilum should be considered in dogs with suspected lymphoma and CD4+ T-cell expansion.
• Comprehensive diagnostic evaluation, including infectious disease testing, is essential.
• This case underscores the importance of a thorough diagnostic approach for complex canine presentations.