The prevalence of hidradenitis suppurativa (HS) in the pediatric population is unknown. We sought to establish standardized overall as well as gender-, age-, and race-specific prevalence estimates of HS among children and adolescents in the United States. We performed a cross-sectional analysis in a heterogeneous sample of 55 million patients across all census regions. We identified 1,240 patients with HS in whom the ratio of girls to boys was 3.8:1. Almost all (96.8%) patients with HS were ≥10 years of age. Overall, HS prevalence was 0.028%, or 28.1 (95% confidence interval [CI] 26.5-29.7) per 100,000 children and adolescents. Standardized prevalence was higher in girls (44.6 [95% CI 41.8-47.5] per 100,000), in patients aged 15-17 years (113.7 [95% CI 106.4-121.4] per 100,000), and among African Americans (78.7 [95% CI 71.0-86.9] per 100,000). Highest prevalence of HS was observed among female adolescents aged 15-17 years who were African Americans (525.1 [95% CI 459.4-597.5] per 100,000) and biracial (253.2 [95% CI 121.4-465.6] per 100,000). Patients with HS who went undiagnosed were not captured, and as such prevalence estimates may be underestimated. HS appears to be a postpubertal disease that disproportionately afflicts girls and African Americans in the pediatric population.

A 71-year-old woman presented with five scalp nodules that were clinically suspicious for pilar cysts. Histopathologic examination showed a proliferation of mitotically active pleomorphic spindle cells arranged into intersecting fascicles in the dermis and subcutis. Tumor cells displayed deeply eosinophilic cytoplasm and expressed desmin but were negative for S100 protein by immunohistochemistry. Before 10 years, the patient was diagnosed with high-grade retroperitoneal leiomyosarcoma and underwent resection with intraoperative radiation. Metastatic disease involving the lungs, liver and soft tissue developed, requiring treatment with resections, radiation and chemotherapy. Owing to the presentation of multiple scalp nodules with microscopic features of leiomyosarcoma in conjunction with the clinical history of retroperitoneal leiomyosarcoma, a diagnosis of metastatic leiomyosarcoma was made. Scalp metastasis from retroperitoneal leiomyosarcoma is extremely rare and portends a poor prognosis. To our knowledge, only two other cases have been reported in the English literature, and a further search discovered only nine additional cases of scalp metastasis from soft tissue leiomyosarcoma of any non-gynecologic anatomic site. This case highlights the striking microscopic similarity between primary cutaneous and metastatic leiomyosarcoma and illustrates the necessity of adequate clinical information and an appropriate index of suspicion in excluding the possibility of cutaneous metastases of leiomyosarcoma from somatic soft tissue.