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Dermatofibroma is a common benign fibrohistiocytic tumour of the skin that usually occurs in mid-adulthood, and has a female predominance. Dermatofibromas show considerable clinical and histological variability. The presence of multiple dermatofibromas is defined, arbitrarily, as >15 lesions.[1] Multiple clustered dermatofibromas (MCD) is a very rare clinical variant, with only 18 reported cases to date.[1-6] We report a patient with MCD, which we believe to be the first reported case in the UK.

A 16-year-old girl presented in February 2011 with a 4-month history of an asymptomatic rash involving her left elbow. There was no history of trauma preceding the eruption. About 4 years previously, a large plaque-like dermatofibroma (first noticed at the age of 3 months) had been excised from her left forearm, which had required a split-thickness skin graft to close the defect (Fig. 1a). The scar had subsequently become hypertrophic, and the patient had been treated with topical and intralesional steroids.

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Figure 1. (a) Plaque-like dermatofibroma (first noticed at the age of 3 months) excised from the left forearm about 4 years before the current presentation. (b) At presentation, multiple clustered red-brown papules were seen on the left outer elbow, coalescing in the centre to form an almost linear plaque.

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On physical examination, 18 firm, nontender, red-brown papules, ranging in size from 3 to 6 mm, were seen, which were distributed over an area of approximately 10 × 10 m on the left outer elbow. Some of the papules, especially in the centre of the lesion, had coalesced to form an almost linear plaque (Fig. 1b). There was no regional lymphadenopathy.

On histopathological examination of two skin biopsies from the affected area, features consistent with a dermatofibroma were seen. There was acanthosis in the epidermis, while numerous collagen fibres and plump to spindle-shaped fibrohistiocytic cells occupied the dermis (Fig. 2). At the edge of the lesion, the tumour cells entrapped the collagen fibres. Immunohistochemistry showed a degree of positivity of the tumour cells for calponin, with minimal staining for smooth-muscle actin. Staining for CD34 and desmin was negative.

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Figure 2. (a) Epidermal acanthosis with numerous collagen fibres and fibrohistiocytic cells occupying the dermis; (b) thick bundles of collagen and plump to spindle-shaped fibrohistiocytic cells within the dermis. Haematoxylin and eosin, original magnification (a) ×20; (b) ×200.

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Routine laboratory investigations, including full blood count, urea and electrolytes, fasting lipids/glucose, liver function tests, and levels of thyroid-stimulating hormone/T4 and serum immunoglobulins, were normal. Serological tests were negative for rheumatoid factor and antinuclear antibody.

Based upon the clinical presentation and histological findings, a diagnosis of MCD was made. Because of its different location and morphology, the plaque-like dermatofibroma that had been excised previously from the left forearm was considered to be a coincidence and not part of the current clinical diagnosis. A short course of localized psoralen and ultravioloet A treatment was found to be moderately effective in flattening the plaque on the elbow. Currently, the patient is not on any treatment, but is under regular follow-up.

Multiple clustered dermatofibromas was first described by Dupre et al. in 1984[4, 7] It is a term used to describe the presence of multiple dermatofibromas clustered in a single anatomic region.[1] MCD can be eruptive, as in this case, or the lesions can increase slowly in number over years. All except one of the reported cases have been described in healthy individuals.[1-6] MCD is more common on the lower half of the body, and seems to develop between the first and third decades in both sexes.[1-6] Intriguingly, three congenital cases of MCD have been described as well.[1, 2, 5] The majority of the reported cases were asymptomatic with no antecedent trauma. No malignant transformation has been reported to date, with follow-up periods of up to 20 years.[5, 6]

The differential diagnosis of MCD includes dermatofibrosarcoma protuberans, atypical fibroxanthoma, nodular fasciitis and dermatofibrosis lenticularis disseminata.[1] Reported effective treatments include surgical excision, with or without grafting, and expectant management. Cryotherapy and intralesional steroids have also been tried.[3, 4]

In conclusion, we report a case of MCD, a rare clinical variant of dermatofibroma, which seems to run a benign course. However, regular follow-up is prudent given the limited number of cases reported to date. Our case also highlights the fact that different clinical variants of dermatofibroma can coexist in the same patient.

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