Large Congenital Cutaneous Mastocytoma Presenting With Recurrent Persistent Blistering: A Case Report

Abstract

Congenital cutaneous mastocytoma is an uncommon disorder characterized by abnormal proliferation of mast cells. It typically presents as a single, small, yellowish-brown plaque, and its diagnosis is generally facilitated by distinctive clinical features, including a positive Darrier's sign. This report presents a case of an unusually large, solitary congenital mastocytoma encompassing nearly the entire circumference of the calf, observed in a newborn boy of Bangladeshi origin. Measuring 13x6 cm, the lesion formed large bullae and subsequent erosions. The perplexing clinical appearance prompted a skin biopsy, revealing monomorphic CD117 (c-KIT) positive infiltration without significant cell pleomorphism, confirming the diagnosis of cutaneous mastocytoma. The patient underwent management with potent and very potent topical steroids, oral antihistamines, and non-adhesive dressings, remaining under long-term follow-up with secondary care dermatology. In reporting this case, our objective is to augment the existing scientific literature by providing additional evidence that cutaneous mastocytomas can display a spectrum of clinical presentations, as illustrated in this case.

Keywords: blister; congenital mastocytoma; cutaneous mastocytoma; mastocytoma; mastocytosis; tryptase.

Figure 1. Erythematous and hyperpigmented plaque on the right calf, exhibiting oedema, bullae, and erosions.

Figure 2. Haematoxylin and eosin staining of the punch biopsy (low power magnification) demonstrated full-thickness infiltration limited to the dermis and reaching down to subcutaneous tissue.

Figure 3. Biopsy with CD117 staining (medium power) showed the infiltrate diffusely and strongly positive for CD117, consistent with mast cell lineage