History and Physical Examination
The patient, a 35-year-old white man, presented with an eruption that dated to his late 20s. The rash consisted of itchy, hyperpigmented macules and papules, most of which measured less than 1 cm. His other unaffected family members often playfully teased him, calling him a "Dalmation puppy." For many years, he sought no care and only recently visited a physician to discuss his condition.
The "itchy spots" on the patient's skin were fewer in number and less symptomatic during the summer, when he spent a great deal of time outdoors, sailing. Although the rash was pruritic, he did not notice any other systemic symptoms. Specifically, he denied headache, flushing, abdominal pain, palpitations, or syncope and was otherwise in excellent health.
Upon physical examination, the patient had red-brown, macular, and slightly papular lesions on his lateral face, neck, chest, back, and upper extremities. Nevi were present in the background but were not the principal feature. Fewer lesions were present on the patient's lower extremities. Rubbing the lesions led to urtication (Figures 1 and 2). Hepatosplenomegaly was not detected clinically.
A biopsy was conducted. Histologic examination revealed an unremarkable epidermis but a scant mononuclear infiltrate surrounding the vasculature. Closer inspection of the mononuclear infiltrate revealed what appeared to be cells with central nuclei and finely granular cytoplasm. Special stains confirmed the increased presence of mast cells (Figures 3 and 4).
What is the most likely diagnosis?
A useful screening test for this patient is measurement of serum levels of:
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Cite this: Whitney A. High. Can You "Spot" the Diagnosis? - Medscape - Jun 10, 2010.