Asymptomatic papule in a young female

A 21-year-old woman presented with an asymptomatic papule below the left collar bone of 2 years duration. It was not associated with itching, pain or discharge. Clinical examination revealed a skin coloured papule below the left clavicle. (Fig. 1) Tenderness was absent. Punch excision of the lesion was done and the tissue was subjected to histopathology. The reticular dermis showed a diffuse tumor-like proliferation of uniform slender spindle-shaped cells arranged in a well-defined elongated as well as intersecting fascicles arranged parallel to the epidermis. (Fig. 2a, b) Immuno-histochemistry revealed diffuse smooth muscle antigen positivity (Fig. 3a); with negative staining for CD34, desmin and epithelial membrane antigen. (Fig. 3b–d)Figure 1: Clinical examination revealed a skin coloured papule below left clavicle.Figure 2: a, b: The reticular dermis shows a diffuse tumor like proliferation of uniform slender spindle-shaped cells arranged in a well-defined elongated as well as intersecting fascicles arranged parallel to the epidermis. (H&E x10, 40).Figure 3: a: IHC shows diffuse positivity for smooth muscle antigen. Figure 3b-d: Negative IHC for CD34, desmin and epithelial membrane antigen. (IHC x40).Question What is your diagnosis? Answer Dermatomyofibroma (DMF). Discussion DMF is an uncommon benign cutaneous tumor originating out of fibroblasts and myofibroblasts. It was first reported in 1991 by Hügel and was later described by Kamino et al. who also proposed the current nomenclature DMF in 1992 [1]. The lesions typically arise on the shoulder areas, axillae, neck, and upper arms of young women [2]. It rarely affects children. They present as asymptomatic, well circumscribed, round to oval/oval skin-colored papules or plaques with smooth surface measuring 1–2 cm. Clinical differential diagnoses are leiomyoma for DMF of small size and dermatofibroma and dermatofibrosarcoma protruberans for larger DMF. Histologically, the tumor is composed of fibroblasts and myofibroblasts in the reticular dermis with relative sparing the superficial papillary dermis. The histopathological hallmark of DMF is parallel arrangement of the myofibroblasts and fibroblasts arranged parallelly to the epidermis [3]. The cells have a very uniform appearance with elongated nuclei having round or pointed ends and one or two small nucleoli. These cells are surrounded by uniformly arranged collagen and elastic fibres arrangement. Inflammatory infiltrate, cellular atypia, and mitoses are absent. Immunohistochemistry shows positivity for smooth muscle actin but negative for cluster of differentiation (CD) 34, epithelial membrane antigen, desmin and S-100 suggesting a myofibroblastic origin of the tumor. Other differential diagnoses like leiyomyoma, neuroma, dermatofibroma and dermatofibrosarcoma protruberans [4]. DMF is managed by simple excision. No malignancy or metastasis has been reported till date. Recurrence post excision is rare. Our patient was a classic case of DMF as described in literature- asymptomatic lesions on upper trunk in a young female. Declaration of patient consent: The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.