Panniculitis is a group of diseases characterized by the localization of the major focus of inflammation to the subcutaneous fat (panniculus adiposus). The lesions may be generalized or localized to specific areas and marked by deep cutaneous nodules that are often ulcerate or fistule, draining pustular, exudative or oily substances. Systemic signs, such as pyrexia, anorexia, lethargy, and depression, are often associated with generalized panniculitis and commonly manifested in waves, heralding the eruption of new lesions.
Multiple factors have been implicated in the etiology of canine panniculitis, including bacterial and fungal infections, nutritional deficiency, vasculopathy, pancreatic diseases, and a variety of immunological (e.g., lupus erythematosus, drug eruption, etc.) and physicochemical (e.g., post-injection inflammation or trauma) factors. In most cases, however, identifying the underlying causes of sterile panniculitis can be a challenging task as this disease may be attributed to one of several causes, each of which may present with similar clinical and histopathological findings.
Although it is considered rare in most veterinary literature, canine idiopathic sterile nodular panniculitis (sterile panniculitis) may be more common than generally described. The fact that miniature dachshunds and poodles are predisposed to sterile panniculitis may suggest a genetic background in the development of the disease.
Sterile panniculitis is diagnosed by dog breed (such as miniature dachshund and corgis, but may occur in all breeds), age (young adult), distribution of lesions (mainly trunk), subcutaneous nodules with/without fistule formation, cytology of pus, bacterial and fungal culture, and histopathology. Periodic acid-Schiff stain may be required to demonstrate or exclude deep fungal infection. Sometimes, Ziel-Nielsen stain may also be performed for rare deep bacterial infections. Preceding and/or concurrent systemic signs, such as fever, lack of appetite, and neutrophilia, may be observed at first admission. Owners may claim a history of previous surgery at the lesion or the area of first onset.
Cytology of pus usually reveals numerous intact neutrophils without bacteria and macrophages with foamy cytoplasm.
Treatment of sterile panniculitis includes tetracycline and niacinamide, and immunosuppressants, such as corticosteroids and cyclosporins. Corticosteroids and cyclosporins can be tapered and finally withdrawn in many cases. However, lesions recur after the discontinuation of immunosuppressants in miniature dachshunds.