# Lymphocytosis and Mycobacteriosis in a 15‐Year‐Old Mixed‐Breed Dog

## TL;DR

An elderly dog with a T-cell cancer and high lymphocyte levels was later found to have a mycobacterial infection, which highlights the need for thorough lymph node testing in similar cases.

## Contribution

This case report highlights the rare co-occurrence of T-cell lymphoid neoplasia and mycobacteriosis in a dog.

## Key findings

- The dog had persistent CD8+ lymphocytosis and lymphadenopathy despite chemotherapy.
- Granulomatous inflammation and Mycobacterium avium complex were identified in lymph node aspirates.
- The dog's condition worsened despite antimicrobial therapy, leading to euthanasia.

## Abstract

A 15‐year‐old mixed‐breed dog with T‐cell lymphoid neoplasia with persistent CD8+ lymphocytosis and peripheral lymphadenopathy despite chemotherapy was referred to the Auburn University Veterinary Teaching Hospital Oncology service approximately 7 months after diagnosis. Lymph node aspirates were performed and assessed by a board‐certified clinical pathologist, which revealed granulomatous inflammation and intracellular, negative staining bacilli. Bacilli were confirmed Mycobacterium avium and other species within the M. avium complex by polymerase chain reaction (PCR) testing. Chemotherapy was ceased and antimicrobial therapy was initiated; however, the lymphocytosis continued to progress, and the dog began to decline, leading to euthanasia around 2 months after referral. Although T‐cell lymphoid neoplasia and mycobacteriosis are rare comorbidities, this case highlights the importance of thorough cytological assessment of lymph node aspirates as part of a complete workup to rule out differential causes of lymphadenopathy. This may have allowed for earlier diagnosis and treatment of mycobacteriosis.