72 Cats, One Pattern: When Lymphadenitis Isn’t Infection or Cancer

Diagnosis of Pyogranulomatous and Neutrophilic Lymphadenitis in 72 Cats Presenting to a Referral Hospital: With a Focus on Steroid-Responsive Cases

Eliana Doyle, Joshua Walker

Background

Pyogranulomatous and neutrophilic lymphadenitis in cats are typically associated with infectious or neoplastic causes, such as feline infectious peritonitis (FIP) or lymphoma. However, some cases lack an identifiable etiology, complicating diagnosis and management. There is limited literature describing the spectrum of causes and particularly the phenomenon of steroid-responsive lymphadenitis, which may represent an immune-mediated condition. This study aimed to characterize underlying diagnoses, diagnostic approaches, and clinical features, with a focus on steroid-responsive cases.

Methods

This retrospective study reviewed medical records of 72 client-owned cats diagnosed with neutrophilic, pyogranulomatous, or mixed lymphadenitis at a single UK referral hospital between 2015 and 2023. Inclusion required cytological or histopathological confirmation from lymph node samples. Cases were categorized by final diagnosis (e.g., infectious, neoplastic, inflammatory, steroid-responsive). Diagnostic workup included variable infectious disease testing, imaging, cytology, and histopathology. A subgroup of cats with steroid-responsive lymphadenitis was analyzed in detail based on clinical features, treatment, and outcomes.

Results

FIP was the most common cause (35%), followed by neoplasia (15%), and steroid-responsive lymphadenitis (12.5%). Other causes included inflammatory disease, bacterial infections, mycobacterial infections, toxoplasmosis, and cases of unclear etiology. Cytology most frequently identified pyogranulomatous or neutrophilic inflammation, though discrepancies between cytology and histopathology were noted.

The steroid-responsive subgroup (9 cats) was typically composed of middle-aged, neutered males presenting with lethargy, fever, anorexia, lymphadenomegaly, and weight loss. No infectious or neoplastic cause was identified despite diagnostic testing. All cats initially improved with glucocorticoid therapy, though 33% experienced relapse, and 22% were euthanized following recurrence.

Limitations

The retrospective design, single-center setting, and relatively small subgroup of steroid-responsive cases limit generalizability. Diagnostic testing was inconsistent and sometimes incomplete due to financial or clinical constraints, raising the possibility of undetected infectious causes. Cytology and histopathology showed limited concordance, and not all cases underwent comprehensive evaluation, introducing potential diagnostic bias.

Conclusions

Pyogranulomatous and neutrophilic lymphadenitis in cats most commonly result from infectious or neoplastic disease, particularly FIP. However, a subset of cases appears steroid-responsive after exclusion of identifiable causes, suggesting a possible immune-mediated etiology. These cases generally respond well to glucocorticoids but may relapse. The study highlights the importance of thorough diagnostic investigation and supports consideration of steroid-responsive lymphadenitis as a differential diagnosis in unexplained cases.

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