Mixed Panniculitis Secondary to Interferon Beta-1a Therapy in a Woman With Multiple Sclerosis

Interferon beta was approved in Spain in 1995 for the treatment of progressive multiple sclerosis. There are 2 main types, interferon beta-1a and 1b, both of which are sold in a variety of formulations, resulting in a range of responses to the same molecule. Local skin reactions are a common adverse effect, and are usually self-limiting. By contrast, panniculitis and lipoatrophy are very rare, and may necessitate discontinuation of treatment. We describe the case of a 43-year-old woman who was diagnosed in 2005 with multiple sclerosis, for which she received several disease-modifying treatments. In October 2009, she began treatment with interferon beta-1a (Rebif 44), which was self-administered subcutaneously 3 times a week, with a favorable response. After 18 months of treatment, induration was observed at the injection sites, on the back of the thighs, and on the outer arms. A few weeks later, ulcerated lesions appeared on the front of the thighs and progressively increased in size. The patient reported that the plaques caused severe pain, which made moving and walking difficult. She reported no fever or systemic upset and her neurological status remained unchanged. Examination revealed 2 ulcers on the front of the thighs of 1 cm diameter. The borders of the ulcers had a scarlike appearance and beneath the ulcers were cavities of about 4 cm in diameter. An indurated plaque of about 15 cm in diameter, with a slightly erythematous surface, surrounded the ulcer and was intensely painful to touch (Fig. 1). These indurated plaques were also present on the external aspect of both arms, although no ulcers were observed. Tissue culture of the ulcers and an incisional biopsy of a plaque from 1 of the thighs were negative. Histopathology revealed a preserved epidermis, sclerosis of the middle