An experimental model of fasciitis-panniculitis. Induction of chronic fibrosing panniculitis in the rat by subcutaneous injections of lipase.

We describe an experimental model of the fasciitis-panniculitis syndrome, which includes eosinophilic fasciitis and its related disorders. Rats were given a single or repeated subcutaneous injections of saline or a 10% lipase solution. The injection sites were studied histologically and histomorphometrically. With few exceptions, the subcutaneous-fascial unit of the saline-injected rats was normal. An acute necrotizing panniculitis with inflammatory involvement of the adjacent fascia was found 2 days after a single injection of lipase. Three to 6 weeks after a single injection of lipase, the subcutaneous fat tissue and fascia were fibrotically thickened and chronically inflamed. Similar but more advanced alterations had developed in animals killed 3 weeks after three weekly injections of lipase. Progressive fibrotic thickening of the subcutaneous-fascial unit was observed following an increasing number of weekly lipase injections. The acute-phase reaction expresses a pattern of steatonecrotic tissue damage. In the ohronic phase, the fibrotically thickened subcutaneous layers typify a reaction pattern analogous to that of the human fasciitis-panniculitis syndrome. This experimental model permits better appreciation of the disorder's nonspecific pathogenesis and may help in the search for alternative therapeutic modalities.