Hindawi Publishing Corporation Case Reports in Medicine Volume 2012, Article ID 109427, 4 pages doi:10.1155/2012/109427 Case Report Simultaneous Occurrence of Erythema Nodosum in Monozygotic Twin Sisters Farhanag Babamahmoodi,1 Abdolreza Babamahmoodi,2 Hamidreza Barani,1 and Leila Delavarian1 1 Department of Infectious Diseases, Mazandaran University of Medical Sciences, Sari, Iran 2 Health Management Research Center, Baqiyatallah University of Medical Sciences, Tehran, Iran Correspondence should be addressed to Abdolreza Babamahmoodi, srm@dr.com Received 12 February 2012; Revised 21 March 2012; Accepted 11 April 2012 Academic Editor: Christos D. Lionis Copyright © 2012 Farhanag Babamahmoodi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Erythema nodosum (EN) is the most frequent clinicopathologic variant of panniculitis with painful red or violaceous nodules on the anterior surfaces of the legs. The condition is a cutaneous reaction that might be associated with a wide variety of disorders or might be caused by medications that produce painful nodules on the shins, and less commonly on the thighs and forearms. In this paper, we describe, for the ﬁrst time in the world, erythema nodosum as the simultaneous presenting complaint of monozygotic twin sisters after streptococcal pharyngitis. This paper might support the eﬀect of heredity in the occurrence of erythema nodosum. 1. Introduction Erythema nodosum (EN) is clinically presented as an acute, ill-deﬁned, nonulcerative, erythematous. and painful eruption, which is usually conﬁned to the extensor aspects of lower extremities. Females comprise the majority of the patients. Erythema nodosum is probably the most common type of panniculitis and a delayed hypersensitivity reaction to a variety of antigens. The condition might be associated with a wide variety of etiologic factors, such as medications, infections, systemic inﬂammatory diseases, malignancies, sarcoidosis, rheumatologic disorders, inﬂammatory bowel diseases, pregnancy, and so on [1]. In 60% of EN cases, no cause is found [2]. Typically, EN is manifested by the sudden onset of symmetrical, tender, erythematous, warm nodules, and raised plaques, usually located on the shins, ankles, and knees and the lesions are often distributed bilaterally [2]. Diagnosis is usually based on a compatible clinical presentation. In patients with atypical features, deep skin biopsy is necessary for conﬁrmation. The typical pathologic presentation is septal panniculitis, with inﬁltration of neutrophils, lymphocytes, and even multinucleated giant cells in the periseptal areas of fat lobules. Vascular deposition of immunoglobulin complexes and complement has been hypothesized as the etiologic factors involved in septal panniculitis, but evidence of this pathophysiological process remains elusive [1]. Treatment of EN should be directed to the underlying associated condition if identiﬁed. In most patients, EN is a self-limited disease and usually nodules of EN regress spontaneously within a few weeks, requiring only symptomatic relief using nonsteroidal anti-inﬂammatory drugs, potassium iodide, cool wet compresses, elevation, and bed rest. Systemic corticosteroids are rarely indicated in EN, and an underlying infection should be ruled out before they are administered [1–3]. 2. Case Report In this case report, for the ﬁrst time in the world, we describe erythema nodosum as the simultaneous presenting complaint of monozygotic twin sisters after streptococcal pharyngitis (Figure 1(a)). It should be noted that both patients provided their informed consent. 2.1. Case One. A married 22-year-old lady presented with a chief complaint of tenderness, heat, and pain in the anterior