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Intracellular success: cytologic findings in an ulcerated submandibular mass from a cat
Penny K Hylton1, Theresa E Rizzi, Robin W Allison
1Department of Veterinary Pathobiology, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK, USA. penny.hylton@okstate.edu
Insights
A Rhodococcus equi infection caused a non-healing skin lesion in a cat. Treatment with rifampin and clarithromycin successfully resolved the pyogranulomatous inflammation and mass.
Area of Science:
- Veterinary Medicine
- Microbiology
- Feline Pathology
Background:
- Submandibular masses in cats can present diagnostic challenges.
- Antibiotic resistance is a growing concern in veterinary infectious diseases.
- Identifying causative agents is crucial for effective treatment.
Observation:
- A 1-year-old domestic shorthair cat presented with an ulcerated, proliferative submandibular lesion unresponsive to initial antibiotic therapy.
- Cytologic examination revealed septic pyogranulomatous inflammation with intracellular pleomorphic bacteria within macrophages and neutrophils.
- Bacterial culture identified Rhodococcus equi, a facultative intracellular coccobacillus.
Findings:
- Rhodococcus equi was identified as the causative agent of the feline submandibular lesion.
- The bacteria were observed intracellularly within macrophages and neutrophils on impression smears.
- Successful treatment was achieved using a combination of rifampin and clarithromycin.
Implications:
- Rhodococcus equi should be considered in the differential diagnosis for cats with pyogranulomatous inflammation and intracellular coccobacilli.
- Antimicrobial susceptibility testing is important for guiding treatment of Rhodococcus equi infections.
- This case highlights the efficacy of rifampin and clarithromycin for treating Rhodococcus equi in felines.
Abstract:
A 1-year-old neutered male domestic shorthair cat had an ulcerated, proliferative lesion in the submandibular area that did not respond to antibiotic therapy. Impression smears from the mass revealed septic pyogranulomatous inflammation, with large numbers of pleomorphic bacteria observed intracellularly within macrophages as well as neutrophils. Bacterial culture was consistent with a diagnosis of Rhodococcus equi, a facultative intracellular coccobacillus capable of replicating within macrophages. The cat's lesion resolved after treatment with rifampin and clarithromycin. R equi should be considered as a differential diagnosis when coccobacilli are recognized within macrophages in cytologic samples.
