Keratoacanthoma Centrifugum Marginatum with Atypical Scar

Keratoacanthoma centrifugum marginatum (KCM) is a rare variant of keratoacanthoma (KA). It is characterized by a progressive peripheral expansion and central healing leaving atrophic scar. It is sometimes confused with squamous cell carcinoma (SCC) both clinically and histopathologically. We here report a case of KCM over the extensor aspect of the right forearm in a 57-year-old man with an abnormal looking scar. 1. Introduction Keratoacanthoma (KA) is a rare benign epidermal tumour, usually diagnosed clinically, and histopathological examination confirms the diagnosis. Most lesions are classical solitary but few unusual rare variants are also described. Keratoacanthoma centrifugum marginatum (KCM) is a rare variant of solitary KA with a clinical course of centrifugal expansion and central restitution or scarring [1]. The cause is unknown but proposed association with UV radiation, chemical exposure, and viral infection has been reported [2]. We hereby report a case of KCM with atypical scar for its rarity and highlight its relationship with SCC. 2. Case Report A 57-year-old male, a farmer by profession, presented in the dermatology OPD with a large plaque extending from below the right elbow onto the extensor aspect of the forearm. The lesion started as an asymptomatic nodule on a normal looking skin and attained its present state over the past 1 year by peripheral spreading and central healing. Nodular ulcerated margin was seen on the proximal and distal aspects in an arciform manner (Figure 1). The whitish intervening scar was traversed in its entire width by narrow strips of a normal looking skin. He was also treated with antitubercular medications from outside without any benefit. General survey, systemic examination, and routine laboratory investigations did not reveal any abnormality. Chest X-ray was normal. The Mantoux test and the screening for HIV were negative. A provisional diagnosis of KCM was made. Histopathological examination of a skin biopsy specimen from the raised margin revealed a huge pitcher like crater extending symmetrically across the upper dermis surrounded by epidermis on all sides (Figure 2). A keratin plug is seen at the bottom of the crater with a dense mixed inflammatory cell infiltrate in the dermis immediately adjacent to the crater (Figure 3). No cellular atypia or involvement of the deep dermis is seen. Based on the above clinical and histopathological findings diagnosis of KCM was made. The patient was referred to the plastic surgery department for excision and grafting. Figure 1: A plaque with nodular ulcerated