Multiple hyperpigmented papules and plaques

Diagnosis: Mastocytosis

The presence of a hyperpigmented skin lesion that becomes pruritic, raised, and erythematous when rubbed (Darier sign) is the major criterion for the diagnosis of cutaneous mastocytosis.¹ Minor criteria include a skin biopsy demonstrating a 4- to 8-fold  increase in the number of mast cells within the papillary dermis and the presence of cKIT mutations.¹ In this case, the patient’s punch biopsy results came back positive for clonal mast cell infiltration of the papillary dermis (FIGURES 2A and 2B), and her physician elicited a slightly positive Darier sign during a follow-up visit.

^{IMAGES COURTESY OF JOSHUA D. SPARLING, MD}

Mastocytosis is characterized by pathognomonic proliferation of clonal mast cells with either cutaneous or systemic involvement.¹ Mast cell expansion most commonly is found in the skin and bone marrow; however, involvement of the gastrointestinal tract, liver, spleen, and lymph nodes also has been documented.¹ Nonhereditary somatic mutations of the cKIT gene have been observed in many studies and may be associated with increased proliferation of clonal mast cells.²

A review of the English-language literature on cutaneous mastocytosis reveals a paucity of reports in darker skin types. However, it is important for clinicians to be able to recognize this disease in all skin types.

Three subcategories. Cutaneous mastocytosis is divided into 3 subcategories: mastocytoma of the skin (1–3 solitary skin lesions), maculopapular cutaneous mastocytosis, also known as urticaria pigmentosa (as seen in our patient; usually ≥ 4 lesions); and diffuse cutaneous mastocytosis (confluent lesions; leathery appearance of skin).^1,3,4 Maculopapular cutaneous mastocytosis, which our patient had, classically develops within the first 6 months of life and presents as hyperpigmented macules and papules.

Keep in mind that systemic involvement in cutaneous mastocytosis occasionally occurs and can be associated with anaphylaxis, flushing, headache, dyspnea, nausea, emesis, diarrhea, abdominal pain, and hepatosplenomegaly.²

Continue to: Narrowing down a broad differential diagnosis