Rhabdomyomatous Mesenchymal Hamartoma Mimicking Basal Cell Carcinoma

Abstract

To the Editor: We read the case report by Biswas1 with great attention because we had recently a similar case of rhabdomyomatous mesenchymal hamartoma (RMH), with increased number of melanocytes, mimicking clinically a basal cell carcinoma. The lesion occurred in an 80-year-old white Hispanic man presented to the dermatologic clinic with a 5-month history of a solitary 5-mm brownish-tan nodule, focally ulcerated, on the left upper eyelid. The patient had a medical history of type II diabetes mellitus, emphysema, and chronic hypertension; left endophtalmitis was diagnosed 30 years ago. The patient had no known history of congenital anomaly. He underwent excision of the lesion, based on a clinical diagnosis of basal cell carcinoma. Histologically, the lesion consisted of numerous disorganized and randomly arranged mature striated skeletal muscle fibers with cross-striations (Figs. 1A, B); pilosebaceous units were also identified. The epidermis showed focal increased number of melanocytes with hyperpigmented basal layer and ulceration. There was no evidence of nesting of melanocytes or atypia, and no malignancy was identified. The dermis revealed pigmentary incontinence and hemorrhage. Masson trichrome highlighted the skeletal muscle fibers (Fig. 1C), and immunohistochemistry examination showed that the muscle fibers were strongly positive for muscle-specific actin (Fig. 1D).FIGURE 1: Specimen taken from the patient's lesion. A, Low-power view showing the morphology of the lesion (hematoxylin-eosin, ×20). B, The tumor was composed of disorganized skeletal muscle fibers (hematoxylin-eosin, ×200). C, Masson trichrome is highlighting the skeletal muscle fiber (×200). D, Immunostaining showing that skeletal muscle fibers are positive for muscle-specific actin (×200).We believe that the clinicopathological features of the lesion described herein are different from those of the lesions previously reported. The present case showed a recent-onset RMH, occurred in an adult man without any recognized congenital malformation. The cases reported in adult patients are scant2-5 (to the best of our knowledge 6, including the present case), and in some of them, the time of evolution is unknown. RMH etiology is not well understood, and some authors have attributed a congenital nature due to the fact that most of the cases are diagnosed during the pediatric age and some of them associated with congenital diseases5; also, the resemblance of the hamartomatous tissue to the normal structures suggests an anomalous development. Hendrick et al6 suggested that traction of the skin may predispose toward the development of RMH. Interestingly, our case and the case in the study of Biswas1 are similar, both having increased number of melanocytes and absence of atypia. Biswas1 explained the melanocytic hyperplasia as an “inductive phenomenon,” a reactive melanocytic proliferation, and we agree with this hypothesis; however, we also believe that the presence of a melanocytic lesion might be a non-related or incidental finding, occurring in the setting of RMH. Particularly in our case, other melanocytic conditions including acquired melanosis should be excluded. Olga L. Bohn, MD Department of Pathology, MetroHealth Medical Center-Case, Western Reserve University, Cleveland, OH Sergio Sanchez-Sosa, MD Department of Pathology, UPAEP University Hospital, Puebla, Mexico