Diagnosis of pyogranulomatous and neutrophilic lymphadenitis in 72 cats presenting to a referral hospital: with a focus on nine cats with steroid-responsive lymphadenitis

ObjectivesThe aim of the study was to review diagnoses and infectious disease testing of cats with neutrophilic or pyogranulomatous lymphadenitis, and describe the history, clinicopathological abnormalities, diagnostic imaging findings, lymph node cytological/histological appearance, treatment response and outcome of steroid-responsive lymphadenitis in cats.MethodsThe medical records of 72 cats documented to have pyogranulomatous, neutrophilic or mixed lymphadenitis between January 2015 and December 2023 at a single referral hospital were retrospectively reviewed.ResultsFeline infectious peritonitis (25/72, 35%) was the most common cause of lymphadenitis and frequently pyogranulomatous. Neoplasia (11/72, 15%) was the overall next most common cause and the most common cause of neutrophilic lymphadenitis. The remaining diagnoses included nine (12.5%) cats with steroid-responsive lymphadenitis, eight (11%) with inflammatory disease, seven (10%) with other suspected bacterial infections, five (7%) with mycobacterial infections, five (7%) with neutrophilic to pyogranulomatous lymphadenitis of unclear cause and two (3%) with toxoplasmosis with variable inflammatory lymphadenitis. Steroid-responsive lymphadenitis cases were often middle-aged (median 7 years 10 months) castrated males (6/9). Common signs included lethargy (7/9, 78%), hyporexia/anorexia (7/9, 78%), pyrexia (7/9, 78%), peripheral lymphadenopathy (6/9) and weight loss (5/9). Frequently affected lymph nodes were submandibular (5/9), popliteal (4/9) and jejunal (4/9). Cytology was more commonly neutrophilic (8/14, 57%) than pyogranulomatous (4/14, 29%). After variable infectious disease testing, all cats received prednisolone (median dose 1.25 mg/kg, range 0.5-2.3) for a median of 5.75 months (range 4-11). All improved initially; relapse occurred in 33% during treatment, after tapering or discontinuation. Two cats (22%) were euthanased after relapse, with one developing neurological signs.Conclusions and relevanceSteroid-responsive lymphadenitis should be considered in cats presenting with inflammatory lymphadenopathy when no identifiable underlying infectious, inflammatory or neoplastic cause is identified, and most cases respond well to glucocorticoid treatment.