Dermatomyofibromas Arising in Children: Report of Two New Cases and Review of the Literature

Pediatric dermatofibromas: Truncal predominance in younger children

Pediatric dermatofibromas are considered rare in young children and have not been well characterized, often misdiagnosed clinically. We performed a retrospective case series of children younger than 18 years with histopathologically diagnosed dermatofibromas at our institutions and evaluated age at onset and diagnosis, sex, lesion location, and size, associated symptoms, change over time, and pre-biopsy diagnosis. Overall, dermatofibromas were most common on the back and chest (20/53; 38%), followed by the legs (15/53; 28%) and arms (12/53; 23%) with the most common pre-biopsy diagnosis of "cyst" (23/53; 43%), followed by dermatofibroma (16/53; 30%), and pilomatricoma (12/53; 23%). Our study reinforces previous findings of truncal predominance of pediatric dermatofibromas, different from adults.

Two cases of congenital dermatomyofibroma

We present two infants with histologically confirmed congenital dermatomyofibromas. Congenital cases are rare with only one prior case reporting presence since birth. Given the benign nature of the lesions and propensity of dermatomyofibromas to resolve without intervention in young male patients, no additional treatments were pursued.

[Anatomoclinical and immunohistochemical study of 8 cases of dermatomyofibroma]

INTRODUCTION

Dermatomyofibroma (DMF) is a rare, benign tumour that is little-known among clinicians. However, it has typical clinical, histological and immunohistochemical features that distinguish it from other fibrous tumours.

METHOD

We report herein on the clinical, histological and immunohistochemical aspects of eight cases of DMF identified between 2008 and 2019 at the dermatopathology laboratory of Strasbourg.

RESULTS

Five men and three women of average age at diagnosis of 21 years and 9 months (range: 9 to 54 years) were included. Lesions ranged in size from 1 to 11cm. Most cases involved the upper body (6 cases), with one case on the abdomen and one on the side. The lesions presented as a solitary asymptomatic red or reddish brown nodule or plaque that gradually developed. The plaques were hard and caused functional discomfort on movement of the neck. Well-circumscribed spindle cell proliferation was noted in the reticular dermis parallel to the epidermis, without mitotic figures or cytological atypia. The subcutis was infiltrated in 5 cases. Expression of calponin was positive in all cases but one, while that of caldesmon, PS100 and desmin was negative. Expression of smooth muscle actin was positive in 2 cases, and both cases were also positive for stromylesin-3. CD34 was positive in 2 cases.

DISCUSSION

DMF is an extensive tumour capable of attaining large diameters and must be completely excised. The main differential diagnoses of DMF are dermatofibrosarcoma protuberans, dermatofibroma, fibrous hamartoma, myofibromatosis and cheloid. It can be identified based on various factors, whether clinical (young age, extensive lesion), histological (horizontal proliferation in the reticular dermis) or immunohistochemical (positive expression of calponin).

Dermatomyofibroma-A rare mesenchymal tumor with maintained horripilation

Dermatomyofibroma is a rare mesenchymal tumor of skin. The major differential diagnosis is dermatofibrosarcoma protuberans. Both lesions are composed of spindle-shaped cells which are CD34-positive. In contrast to the malignant counterpart, the tumor cells in dermatomyofibroma are without any evidence of COL1A1-PDGFB gene rearrangement. We present a case of axillary dermatomyofibroma in a 31-year-old woman. A hitherto undescribed clinical phenomenon is a maintained horripilation in contrast to dermatofibrosarcoma protuberans.