Feline histoplasmosis presenting with bone and joint involvement: clinical and diagnostic findings in 25 cats.

OBJECTIVES: The aim of this study was to describe clinical and diagnostic findings in cats with bone and joint disease associated with histoplasmosis.

METHODS: Medical records from between 2011 and 2017 were reviewed. Inclusion criteria required: (1) diagnosis of histoplasmosis by cytology, histology, urine or serum Histoplasma antigen testing, or culture; and (2) lameness or joint effusion as a presenting complaint or physical examination finding.

RESULTS: Twenty-five cases met the inclusion criteria. Four had incomplete records, but available data were included when applicable. Lameness was a presenting complaint in 17/21 cats and was the only complaint in 9/21 cats. Initial diagnosis was made by cytology in 22/25 cats and by culture, urine antigen and necropsy in one case each. Diagnostic cytology samples included synovial fluid (n = 13), lymph node (n = 5), skin (n = 2), lung (n = 1) and bone (n = 1). Two additional cases had synovial fluid examined but no organisms present. Inflammation was present in all synovial fluid samples examined. Biopsy was obtained in two cats and histologic diagnoses included osteomyelitis with no infectious organisms identified and severe lymphoplasmacytic synovitis suggestive of feline periosteal proliferative polyarthritis. Histoplasma urine antigen test was positive in 7/12 cats.

CONCLUSIONS AND RELEVANCE: Inflammatory arthritis is common in cats with histoplasmosis, with lameness a common presenting complaint. Organisms are found in synovial fluid cytology in most cases. If not, appropriate additional diagnostics must be pursued.