Multiple skin-colored to red-brown papules scattered on the extremities of a 17-year-old male

Summary: A 17-year-old male presented with multiple asymptomatic papules on his extremities, which had increased in number over time. Previous biopsies were compatible with eruptive dermatofibromas. There was no family history of similar lesions. Physical examination demonstrated many skin-colored to red-brown 1-5 mm papules scattered on the upper and lower extremities. ANA and HIV screening were negative. Biopsies of two distinct papules showed a dermal histiocytic infiltrate with mast cells. The cells of interest were positive for factor XIIIa and negative for CD68, alpha-1 antitrypsin, Langerin, and SOX10. Alcian blue demonstrated prominent dermal mucinosis. The mast cell population was confirmed with CD117 and tryptase. The patient was diagnosed with progressive mucinous histiocytosis (PMH), which is a rare, benign, skin-limited disorder. Very few cases have been reported, with the majority observed almost exclusively in females. It presents with skin-colored to red-brown papules that are characterized by prominent mucin histologically. Reported treatment options include excision, intralesional steroids, and thalidomide. Given our patient’s lesions are asymptomatic and not cosmetically bothersome, he and his family opted for monitoring. This unique case of PMH contributes valuable clinical and histopathologic findings, which can enhance awareness of this uncommon disease, and ultimately aid in earlier diagnosis and management.