Medallion-like dermal dendrocyte hamartoma on the abdomen

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A one-year-old girl presented with two asymptomatic erythematous plaques on her abdomen since birth. The plaques enlarged proportionately with the normal growth. Personal and family history were unremarkable, and her mother denied having received medication during pregnancy. Physical examination revealed two well-circumscribed reddish-brown infiltrated plaques, each measuring 2-5 cm in diameter, on her abdomen with a subtle wrinkled appearance [Figure 1]. A skin biopsy specimen obtained from the edge of the plaque showed partially dilated venous structures and a band-like pattern of spindle cell proliferation in the reticular dermis [Figure 2a-b], which was positive for CD34 [Figure 2c] and factor XIIIA [Figure 2d], and negative for CD31, smooth muscle actin (SMA), neuron-specific enolase (NSE), S-100, and Melan A. Thus, the diagnosis of medallion-like dermal dendrocyte hamartoma (ML-DDH) was made. The patient did not receive further treatment and was asked to follow up regularly.

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Figure 1:

Two infiltrated erythematous plaques with distinct borders and wrinkled appearance.

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Figure 2a:

Bandlike spindle cell proliferation in the reticular dermis and dilated venous structures (Haematoxylin & eosin, 25x).

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Figure 2b:

Bandlike spindle cell proliferation in the reticular dermis and dilated venous structures (Haematoxylin & eosin, 100x).

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Figure 2c:

Immunohistochemical staining showing CD34 positivity (100x).

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Figure 2d:

Immunohistochemical staining showing factor XIIIA positivity (100x).

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ML-DDH, also referred to as plaque-like CD34-positive dermal fibroma, is a rare benign congenital cutaneous disease with an unclear aetiology. Rodríguez-Jurado first reported three young females in 2004 with congenital atrophic well-circumscribed patches on the neck or upper trunk.¹ Subsequent research demonstrated variable clinical features with common histopathological findings, recommending plaque-like CD34-positive dermal fibroma as an adjustment to nomenclature. It is typically characterised by asymptomatic, well-defined, round or oval red-brown plaques with wrinkled surface and visible blood vessels on the trunk, although skin-coloured papules and subcutaneous nodules on limbs are reported as rare presentations.² Most published cases are present at birth or at a young age, and predominantly seen in females. Histopathological features reveal band-like spindle cell proliferation in superficial and mid-dermis with small nuclei and inconspicuous nucleoli, and may occasionally extend into the subcutaneous fat. Other changes, such as epidermal atrophy, multiple dilated venules, and reduction of elastic fibres and adnexa have been described. Immunohistochemistry of ML-DDH is positive for CD34 and vimentin, with some spindle cells also co-expressing factor XIIIa, but negative for S-100 and Desmin.³

The differential diagnosis includes spindle cell tumours, particularly congenital atrophic dermatofibrosarcoma protuberans, fibroblastic connective tissue naevus, and pseudoatrophic macules of neurofibroma. The congenital atrophic dermatofibrosarcoma protuberans is a rare, locally aggressive soft tissue dermal tumour, and shares similar clinical and immunohistochemical features with ML-DDH. However, lesions of this type usually enlarge progressively rather than growing proportionately along with the body surface. In challenging or borderline cases, multiplex reverse transcription polymerase chain reaction (mRT-PCR) and dual colour fusion fluorescence in situ hybridization have been used for the detection of COL1A1-PDGFB gene fusion that is exclusively found in dermatofibrosarcoma protuberans.⁴ Fibroblastic connective tissue naevus is one of the subtypes of connective tissue naevus, which may also present as solitary, asymptomatic, and slowly growing plaque or nodules. Its distinctive histopathological features include spindle-shaped cells that are interlaced and disorganised within the subcutaneous fat. Furthermore, staining for CD34 in fibroblastic connective tissue naevus is typically weak and patchy, whereas that in ML-DDH is strong and diffuse.⁵ Pseudoatrophic macules of neurofibroma are a subtype of cutaneous neurofibromas, characterised by clearly defined atrophic skin patches. The key distinction lies in the positive immunohistochemical staining for S-100 and NSE, with concurrent negativity for CD34 and Factor XIIIa.⁶

In conclusion, differentiating ML-DDH from other CD34-positive spindle cell tumours is of utmost importance. And unnecessary interventions should be avoided, as ML-DDH is a benign tumour with an extremely low recurrence rate after surgical excision.