Diagnosing & Treating Canine Sterile Panniculitis

Sterile panniculitis is inflammation of subcutaneous fat in the absence of microbial infection. The pathogenesis is not thoroughly understood, and the disorder is commonly misdiagnosed as deep pyoderma, cutaneous cyst, or cutaneous neoplasia. This study evaluated 10 dogs with sterile panniculitis, comparing underlying disease, diagnostic findings, and treatment outcomes. There was no significant breed predilection. Four dogs had atopic dermatitis, 2 had acute pancreatitis, 1 had primary hypoadrenocorticism, and 3 had no history of other disease. There was no recent history of vaccinations or injections at the site of the lesions. Seven dogs had well-circumscribed firm nodules containing pleomorphic spindle cells and rare inflammatory cells. Three dogs had soft fluctuant nodules containing adipose cells and numerous inflammatory cells. Treatments included surgical excision (n = 1), systemic antibiotics (n = 1), intralesional injections of dexamethasone (n = 1), topical dexamethasone ointment (n = 4), oral prednisolone plus cyclosporine (n = 2), and oral prednisolone alone (n = 1). Initial response was good in all cases, with regression of lesions within 1 week. Two dogs relapsed within 2 months but responded to the same treatments within 1 week.

Commentary: Adult-onset panniculitis is uncommon, especially diffuse nodular presentations. The lesions are dramatic, the dog is in pain, and signs of systemic illness are present. However, diagnoses in cases where lesions are limited to one or just a few nodules are challenging. Diagnostic differentials include foreign body reactions, inclusion cysts, tumor, warble, or focal trauma. Fine-needle aspiration (FNA) is typically the diagnostic test of choice with solitary or few nodules, but FNA results were misleading in 8 of these 10 cases. In my experience, samples of deep dermis and panniculus require a deep wedge or excisional biopsy; routine punch biopsy is too superficial. Of note, in 2 dog, focal nodular lesions developed concurrently with pancreatitis. This clinical factoid should be recorded, as pancreatitis is more common than panniculitis—perhaps these lesions are more common than this article suggests. Topical glucocorticoids for treating focal or multifocal lesions are an option if a potent steroid is used. Another option would be a combination of DMSO and glucocorticoids. —Karen Moriello, DVM, Diplomate ACVD

Sterile panniculitis in dogs: New diagnostic findings and alternative treatments. Kim H-J, Kang M-H, Kim J-H, et al. VET DERMATOL 22:352-359, 2011.