The majority of dermatomyofibromas present as red-brown discolored plaques or nodules4
. Dermatomyofibroma develops most frequently in young female patients, and commonly occurs on the shoulder, upper arm, axilla, neck, and/or the upper trunk. In a recent study, female and male children and adolescent atients were reported to be affected equally, in contrast to the female dominant pattern in adults2
To date, only six cases have been reported under the age of 5 years, all of them being boys. Among those, three cases occurred in the infantile period1-6
. It has been suggested that dermatomyofibroma in male children tends to show spontaneous regression after childhood, whereas the lesions continue to grow in female patients, possibly due to the effects of female hormones2,5
. However, there is no proof for this hypothesis. Further studies evaluating the expression of hormone receptors in the tissue specimen will be of value to clarify this hypothesis.
Histologically, most cases of dermatomyofibroma have a benign, ill-defined, plaque-like dermal proliferation of spindle-shaped tumor cells often arranged parallel to the epidermis1,2
. The tumor cells fill the reticular dermis and sometimes extend into the upper part of the subcutaneous layer, whereas the papillary dermis and adnexal structures are spared. The overlying epidermis appears normal, although sometimes a mild basal hyperpigmentation is observed5
. The elastic fibers are preserved; this finding provides a clue to the diagnosis, because dermatofibroma and hypertrophic scars have altered elastic fibers5
. Immunohistochemistry should be considered for cases that have non-specific histopathological features. The spindle cells stain positive for vimentin and are occasionally positive for smooth muscle actin. However, they are negative for S-100 protein, desmin, and CD347
Clinically, scar or keloid should be distinguished from dermatomyofibroma. However, frequently there is a preceding history of trauma or surgery in a scar or keloid. In addition, a whorl-like or nodular structure with no or few adnexae is observed3
. The histological differential diagnosis of dermatomyofibroma includes dermatofibromas, dermatofibrosarcoma protuberans, and fibrous hamartoma of infancy. Dermatofibromas are not as plaque-like and are more likely to show epidermal hyperplasia and a haphazard architecture as opposed to the fascicles of dermatomyofibromas, which are parallel to the epidermal surface8
In addition, there is a reduction or loss of elastic fibers and involvement of adnexal structures4
. Dermatofibrosarcoma protuberans shows a more intense cellular infiltration with storiform architecture and, unlike dermatomyofibroma, it is positive for CD344
. In the present case, a fibro/myofibroblastic proliferation, as in fibrous hamartomas of infancy, should have been part of the differential diagnosis, since the patient was an infant. However, fibrous hamartomas of infancy could be excluded because they consist of three distinct components: the combination of fibrocollagenous trabeculae composed of bland spindle cells, small nests of loosely arranged oval or stellate mesenchymal cells set in a myxoid stroma, and mature fat2
The prognosis of dermatomyofibroma is favorable and surgical excision is the treatment of choice. No recurrence or metastasis has been reported yet. In this case, the patient was observed closely without treatment, since dermatomyofibroma in males may regress spontaneously after childhood6
In summary, dermatomyofibroma is a distinctive benign dermal myofibroblastic proliferation that is rare in children, especially during infancy. However, clinicians should consider the diagnosis when characteristic myofibroblastic proliferation is present on skin biopsy.