Lobular panniculitis at the site of subcutaneous interferon beta injections for the treatment of multiple sclerosis can histologically mimic pancreatic panniculitis. A study of 12 cases.

Background: Thrombosis, mucinosis and necrosis are well-described complications of subcutaneous interferon beta injections.
Methods: We report 12 incisional biopsies from subcutaneous interferon beta injection sites in 12 multiple sclerosis (MS) patients from a single neurologist's practice.
Results: We identified abscesses (two cases) or induration (two cases) in acute clinical lesions and lipoatrophy (eight cases) in chronic lesions (biopsied over a year after symptom onset at injection sites). Biopsies from three acute lesions showed vascular thrombosis, dermal mucinosis, lobular neutrophilic panniculitis, necrosis, calcification and hemosiderin deposition (biopsied 2 weeks to 2 months after symptom onset). Two cases contained sterile abscesses. Five of the eight chronic cases presented as hard, indurated lipoatrophy with livedo reticularis. Their biopsies showed subcutaneous calcification and lipoatrophy. Biopsies from the early calcific suppurative and late calcific atrophic phases histologically resembled the early and late phases of subcutaneous saponification in pancreatic panniculitis.
Conclusions: Reactions at the site of subcutaneous interferon beta injections are common. Lipoatrophy can be clinically identified in 39 of 85 MS patients (46%) receiving subcutaneous interferon beta injections for 1 year or longer in our practice. A reaction to interferon should be considered in the differential diagnosis of biopsies that show features of pancreatic panniculitis.