PMC4156028_01
A solitary, 3.5 x 6.5 cm, non-tender, minimally elevated plaque with edematous central shiny skin made more apparent on scratching the lesion with the blunt end of a pin (positive Darier's sign) with peripheral marginal hyperpigmentation over the left elbow.
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On scratching the lesion with the blunt end of a pin, the central shiny skin became edematous and itchy (positive Darier's sign) ( Figure 1).
a, Dense monomorphic inflammatory infiltrate in upper and mid dermis;
b, Dense monomorphic inflammatory infiltrate consisting of round to oval cells with clear cytoplasm noted at 40x magnification.
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A 5 mm biopsy of the skin tissue obtained from the center of the lesion revealed a dense monomorphic inflammatory infiltrate consisting of round to oval cells with clear cytoplasm and centrally located nuclei in the upper and mid dermis ( Figure 2a, 2b).
Metachromatic staining of the monomorphic mast cells with Toluidine blue staining.
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Special staining with toluidine blue revealed metachromatic staining of the monomorphic mast cells, confirming the diagnosis of mastocytoma ( Figure 3).
Complete subsidence of the lesion with residual marginal pigmentation noted at the end of three months of therapy.. The central atrophic scar due to biopsy can be seen in the centre of the lesion.
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Treatment was continued with only a once a day application of topical tacrolimus for a month after clinical resolution to prevent further recurrence ( Figure 4).