Feline mycobacterium, what are the findings?

Computed tomographic findings in cats with mycobacterial infection

Alison Major, Andrea Holmes, Christopher Warren-Smith, Stephanie Lalor, Rebecca Littler, Tobias Schwarz, Danièlle Gunn-Moore

Background
Feline mycobacteriosis is an emerging veterinary health concern, with increasing cases reported worldwide. The infection is primarily caused by Mycobacterium microti and Mycobacterium bovis, leading to multisystemic disease. Diagnosis is challenging due to the variability in clinical presentation and the limitations of current laboratory techniques. Computed tomography (CT) has advantages over radiography for identifying mycobacterial disease, but its diagnostic utility in cats has not been well characterized. This study aimed to describe the CT features of mycobacterial infections in cats.

Methods
A retrospective review was conducted on CT scans from 20 cats with confirmed mycobacterial infections between 2009 and 2015. Diagnoses were confirmed via Ziehl–Neelsen staining, culture, PCR, or interferon-gamma release assays. CT scans were evaluated for thoracic, abdominal, skeletal, and soft tissue abnormalities.

Results
Thoracic abnormalities were present in 19/20 cats, including bronchial thickening (9/20), alveolar patterns (8/20), ground-glass opacity (6/20), and structured interstitial lung changes (15/20). Tracheobronchial, sternal, and cranial mediastinal lymphadenomegaly were common (16/20). Extra-thoracic findings included abdominal lymphadenomegaly (8/13), hepatosplenomegaly (7/13), osteolytic/osteoproliferative skeletal lesions (7/20), and cutaneous or subcutaneous masses (4/20). In two cases, cavitated pulmonary lesions were detected, a feature rarely reported in feline mycobacteriosis.

Limitations
This was a retrospective study with inherent biases, including variability in imaging protocols and lack of histopathologic confirmation for all lesions. The absence of standardized contrast enhancement techniques may have affected lymph node and organ assessments. Additionally, resolution limitations in awake CT imaging may have led to underestimation of small lesions.

Conclusions
CT imaging provides valuable insights into the multisystemic nature of feline mycobacteriosis, often revealing thoracic, abdominal, and skeletal involvement. Given the diversity of CT abnormalities, mycobacterial infection should be included in the differential diagnosis for cats with unexplained lymphadenopathy, respiratory disease, or bone lesions. Future studies should focus on refining imaging protocols and correlating CT findings with treatment outcomes.

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