Dermatology Online Journal

Dermatomyofibroma mimicking granuloma annulare
Natividad Cano Martínez MD¹, Carmen Fernández-Antón Martínez MD¹, Lucía Barchino Ortiz MD¹, Manuel Lecona Echevarría MD², Minia Campos Domínguez MD¹
Dermatology Online Journal 17 (6): 3

1. Department of Dermatology
2. Department of Pathology
Hospital Universitario Gregorio Marañón, Madrid, Spain

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Abstract

We report the case of a 9-year-old girl with a lesion on the posterior aspect of the neck, which was clinically compatible with granuloma annulare. An incisional biopsy was performed and the result of the biopsy was consistent with a fibrohistiocytic proliferation. After the total excision of the lesion, the definitive diagnosis of dermatomyofibroma was determined. Dermatomyofibroma is a benign and rare proliferation of myofibroblasts of the skin. Dermatomyofibroma is a solitary and slowly growing tumor. It is more common in adolescents and young adults, with a female preponderance. Dermatomyofibroma presents clinically as a papule or nodule. It may be slightly hyperpigmented. It is usually located on the upper trunk, axilla, upper arm, or neck. The treatment of choice is complete excision and the prognosis is excellent.

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Case report

A 9-year-old girl presented to our pediatric dermatology clinic with a cervical plaque that had been present for six months. She complained of slight pruritus. The plaque had been treated by her primary care physician as neurodermitis with mometasone without improving.

Figure 1
Figure 1. An ill-defined annular 25 cm plaque on the posterior aspect of neck. Mild hyperpigmentation was seen. The biopsy scar is noticeable.

On physical examination a 2.5 cm plaque with mild hyperpigmentation on the posterior aspect of her neck with rounded morphology and elevated borders is noted (Figure 1). These clinical features suggested the clinical diagnosis of granuloma annulare. We performed a 4 mm punch biopsy of the lesion to confirm the clinical diagnosis and this showed a fibrohistiocytic proliferation, which has many differential diagnoses.

The mother of the patient reported the lesion had grown since the last visit. The lesion was excised completely.

Figure 2	Figure 3
Figure 2. Histologic examination of the specimen showed an ill-defined, uniform spindle cell neoplasm filling the reticular dermis and the superficial part of the hypodermis. Figure 3. Spindle-cell proliferation seen on a matrix of collagen fibers. The spindled cells are arranged in parallel to the surface of the skin. These cells were distributed forming fascicles or bands.

The histopathology of the lesion showed an ill defined fibrohistiocytic infiltration within. the deep dermis and superficial part of the hypodermis (Figure 2). The plaque consisted of a spindle-cell proliferation on a matrix of collagen fibers in the dermis with a parallel arrangement to the skin surface. These cells were distributed forming fascicles or bands (Figure 3). The cells had elongated shape, eosinophilic cytoplasm, and fine nuclear chromatin. Some cells had small nucleoli. The cells lacked mitoses. Adnexal structures were spared. Orcein staining showed abundant elastic fibers.

Immunohistochemical evaluation showed that the spindle-shaped cells reacted positively for vimentine and there was no reactivity with actin, desmin, factor XIIIa, S-100, CD34, and CD68.

Based on these histologic and inmunohistologic features, the diagnosis was compatible with dermatomyofibroma, which was completely excised. The patient has shown no signs of recurrence after 1 year of follow-up.

Discussion

Dermatomyiofibroma represents a relatively rare cutaneous mesenchymal neoplasm of fibroblastic/myofibroblastic differentiation.

The fibrohistiocytic tumors of the skin are a heterogeneous group of dermal/subcutaneous mesenchymal neoplasms which show fibroblastic, myofibroblastic, and histiocytic differentiation [1]. Dermatomyofibroma was first described by Hügel in 1991 under the name, plaque-like dermal fibromatosis [2, 3]. One year later it was described by Kamino under the name dermatomyofibroma. The latter name has also become accepted in Europe [4].

Dermatomyofibroma is a solitary, slowly growing and benign tumor. Cases have been reported with multiple dermatomyofibromas in a single anatomical area [5]. It is primarily found in young adult females and in preteen children. The dermatomyofibroma is more common in women than in men. The average age of presentation in women is 31.4 years and men 12.3 years. There are case reports of male patients as young as one year old [3].

It is remarkable that the affected females are significantly older than the affected males. The cause of this difference in sex and age distribution is not clear. Possibly dermatomyofibroma may regress spontaneously after childhood in males. The tendency of dermatomyofibroma to occur in postpubescent females and prepubescent males may indicate that this tumor could be responsive to hormones, as has been suggested by some authors [3, 6]. More studies are needed to elucidate the characteristic distribution of gender and age.

Dermatomyofibroma presents clinically as a plaque or nodule, more palpable than visible. In the literature there are annular or linear variants that are rare [7, 8]. The overlying surface can be slightly pigmented. Normally the dermatomyofibroma is small, usually measuring 1 to 2 cm in diameter, although there have been reported cases of giant dermatomyofibromas [8]. The sites of predilection are the anterior abdominal wall in adult women, the posterior neck in prepubertal boys, and the shoulder and axilla in both genders [3, 6].

The clinical differential diagnosis includes dermatofibroma, granuloma annulare, pseudolymphoma cutis, hypertrophic scar, cyst, and connective tissue nevus [9].

Histological examination shows an ill-defined, uniform, spindle-cell proliferation on a matrix of collagen fibers in the dermis with a parallel arrangement to the skin surface. These spindle cells show fibroblastic and myofibroblastic differentiation. The cytoplasm is pale, eosinophilic, and ill-defined. The nuclei are elongated and well-defined. On the other hand, mitotic figures are rarely seen. Spindle cells are arranged to form well-defined fascicles. Collagen fibers are thin, crisscross between the spindle cells, and stain with Masson trichrome. Elastic fibers are not reduced in number, but may be increased in number and even fragmented. This would be a distinctive feature that would help us in the differential diagnosis. Elastic fibers are altered in dermatofibroma, hypertrophic scar, dermatofibrosarcoma protuberans and piloleiomyoma. Elastic fibers stain with orcein and Verhoeff van Gieson [9, 10].

The tumor is located in the deep dermis and subcutaneous tissue. The epidermis is usually spared, but can be slightly hyperpigmented. Adnexal structures are spared [1-10].

Although the histological features facilitate a diagnosis pf dermatomyofibroma, it is sometimes difficult. The immunohistochemical features of the dermatomyofibroma may help us to diagnose the tumor. The spindle-shaped cells react positively for vimentin and can be stained for smooth muscle actin. The expression of actin depends on the patient's age and activity of neoplastic cells [9]. There was no reactivity with desmin, Factor XIIIa, S-100 and CD34 in our case. These results confirm the fibroblastic and myofibroblastic differentiation [2-11].

This staining pattern helps to exclude the main differential diagnoses. Dermatofibrosarcoma protuberans (DFSP) is more cellular than dermatomyofibroma. The spindle-shaped cells are grouped together forming short fascicles with a storiform pattern. The tumor shows honeycomb infiltration of adipose tissue and there is involvement of adnexal structures. With regard to immunohistochemistry, DFSP stains for CD34. It is difficult to differentiate the two tumors with a superficial biopsy [1, 9, 10]. (Table 1)

Dermatofibroma shows a nodular proliferation of myofibroblasts, fibroblasts, and histiocytic cells presenting a stellate morphology. The dermatofibroma exhibits abundant vascularization and breaches the adnexal structures. Elastic fibers are decreased in number or absent and stain positively for factor XIIIa. When the dermatofibroma has many myofibroblasts is difficult to distinguish from dermatomyofibroma [1, 9, 10].

Piloleiomyoma is a tumor with more cellularity than dermatomyofibroma and affects the deep dermis. The cells have cigar-shaped nuclei. The center of the lesion has interdigitated fascicles and in the periphery there is an infiltrative pattern. The immunohistochemical features include positivity for desmin and smooth muscle actin [10].

Neurofibroma is a tumor that is usually solitary, affecting the superficial dermis. Its component cells are usually spindle cells arranged chaotically on a stroma that is vascular, fibrotic, edematous, or myxedematous. Immunohistochemistry of the tumor is positive for S-100, but CD34 can be positive or negative [10].

The connective tissue nevus presents a very subtle clinical appearance that can be confused with normal skin. Histopathologically is an ill-defined area of increased dermal collagen that shows a normal number of fibroblasts. Elastic fibers may be increased, decreased, or normal in number [9]. Dermal fibromatosis is difficult to distinguish from a small biopsy of dermatomyofibroma.

Dermal fibromatosis presents as poorly demarcated dermal and subcutaneous nodules or plaques, which are formed by bundles of fibroblasts and myofibroblasts. In dermal fibromatosis there may be a hypocellular focus with thick collagen fibers and there may be a hypercellular focus with thin collagen fibers. The skin can invade the aponeurosis, adjacent fascia, and skeletal muscle [9, 10].

Fibrous hamartoma of infancy and plexiform fibrohisticytic tumor are two rare soft tissue neoplasms of childhood and young adulthood, which are in the differential diagnosis. Both lesions are located in the subcutaneous tissue and rarely affect the dermis. On the contrary, dermatomyofibroma is generally affecting the dermis and sometimes can affect the superficial subcutaneous tissue [3]. Dermatomyofibromas have not been reported to recur or metastasize. The treatment of choicefor dermatomyofibroma is total excision of the lesion and it has a good prognosis.

It is important to establish the diagnosis of this entity. The dermatomyofibroma must be distinguished from other fibrohistiocytic tumors of intermediate or malignant nature.

References

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