Clinical Case of Sterile Nodular Panniculitis

Introduction. Sterile nodular panniculitis is a rare disease of the subcutaneous adipose tissue. This condition remains insufficiently studied and requires timely and accurate diagnostic work-up. The aim of this article was to remind general practitioners and surgeons to include sterile nodular panniculitis in the differential diagnosis when presented with patients having primary multiple nodular lesions or when additional nodular foci appear during the treatment of soft tissue abscesses.

Case description. A 9-year-old intact female mixed-breed dog weighing 11.5 kg was referred from an external clinic with painful subcutaneous nodules distributed over the body, some of which had ulcerated during a 6-month observation period. The dog had been kept indoors throughout its life, with no travel outside Moscow or to other regions. Ectoparasite and endoparasite control was irregular. Previous therapy over the preceding 6 months included intermittent short courses of amoxicillin with clavulanic acid (7 days each); one week before presentation, another course of antibacterial therapy with Synulox at 12.5 mg/kg was initiated. Dermatological examination revealed multiple firm nodules ranging from 0.5 cm to 3 cm in diameter on the back and flanks; fluctuation was palpable in some nodules. Multiple fistulas with active purulent exudation were present, along with nodules measuring 0.3 to 2 cm on the abdomen and over the mammary gland region (fifth caudal package on the right and fourth on the left). Bacterial culture yielded methicillin-resistant Staphylococcus haemolyticus . Azithromycin at 11 mg/kg/day was prescribed. During antibiotic therapy, the nodules decreased in size but did not completely resolve. Histopathological examination confirmed locally extensive pyogranulomatous inflammation; special staining of tissue sections revealed no evidence of mycobacterial or fungal infection. Methylprednisolone at 1 mg/kg was initiated. On the second day of methylprednisolone treatment, the dog's condition improved markedly, with significant reduction in exudation, decrease in fistula diameter, and rapid regression of nodules. At the follow-up examination 10 days later, fistulous tracts were no longer present, and only two nodular lesions remained.

Discussion. The incidence of sterile panniculitis is quite rare. The diagnostic challenge is compounded by the fact that this diagnosis was not suspected at the initial presentation to the external clinic a frequently encountered scenario. This makes the present clinical case valuable not only for dermatologists but also for general practitioners and surgeons, who should consider it in the differential diagnosis (abscess, mammary neoplasia).

Conclusion. The presented clinical case demonstrates that sterile nodular panniculitis, being a rare condition, is often masked by more common pathologies in its early stages, leading to irrational antibiotic use and the development of secondary resistant infection. The key to successful diagnosis is a comprehensive approach, including cytological and histopathological examination with exclusion of infectious agents.

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