Darier's sign in urticaria pigmentosa–significance of perivascular eosinophilic infiltration

Urticaria pigmentosa is characterized by the accumulation of mast cells in cutaneous and extracutaneous organs. Multiorgan involvement frequently causes systemic symptoms such as pruritus, flushing, abdominal pain, or headache due to mast cell degranulation releasing histamine, substance P, and other chemical mediators.1,2 Rubbing/stroking of the skin or other mechanical stresses induce an urticarial reaction called Darier's sign, which is a specific diagnostic sign for urticaria pigmentosa.3 However, the pathological and immunohistological features of Darier's sign have not yet been described. We investigated the histopathological features of urticaria pigmentosa in specimens presenting with or without Darier's sign. In our department, 18 were diagnosed as urticaria pigmentosa (mean age 41.5 months, male: female ratio 12:6) (Supplementary Methods). Solitary lesions were observed in 6 cases while 12 cases showed multiple lesions. A family history of urticaria pigmentosa was positive in 3 patients and all cases had multiple lesions (Supplementary Table 1). Reportedly, all patients exhibited a positive Darier's sign at the time of their first visit. Among the 18 specimens obtained, 5 were obtained from Darier's sign areas within 30 min after scratching the site, and 13 were obtained from nonscratched lesions without Darier's sign (Supplementary Methods). Darier's sign was induced using pen friction. Histopathologically, the non-Darier's sign group (Fig. 1AeD) showed cuboidal mast cell infiltration in the dermis to subcutis (Fig. 1AeD). These accumulated mast cells showed abundant cytoplasmic granules (Fig. 1C). Negligible perivascular lymphocytic and neutrophilic infiltration was found in all cases. Minimal perivascular eosinophilic infiltration was found in 11 of 13 specimens. However, all cases belonging to the Darier's sign group (Fig. 1F-I) showed that most of the accumulatedmast cells were degranulated with scarce intracytoplasmic granules present (Fig. 1H), and significant perivascular eosinophilic infiltrationwas observed in all specimens (Fig. 1I). Mild to moderate edema was noted in the papillary dermis (Fig. 1G). Only one case showed concomitant intravascular neutrophilic infiltration. The number of perivascular eosinophils was significantly higher in the Darier's sign group than in the non-Darier's sign group (P < 0.0126) (Fig. 2A). Based on the results of a recent study emphasizing the role of substance P in eosinophil migration,4 we examined the immunohistological distribution of substance P in specimens with urticaria pigmentosa with and without Darier's sign. The immunoreactive