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A man in his 60s presented to our dermatology outpatient department with a 5-year history of pruritic papules on the right side of his lower back. He was otherwise healthy, with no family history of a similar condition. Physical examination results showed multiple dome-shaped, skin-colored, firm papules on his right lower back, arranged in a blaschkoid distribution (Figure 1A). The lesions varied in size, with some coalescing into irregular-shaped, larger papules. Telangiectasis could be seen on some of the lesions. A skin biopsy was performed on his back and submitted for further histopathologic analysis (Figure 1B and C).
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C. Mucinous nevus
Examination of the punch biopsy specimen revealed hyperkeratosis, parakeratosis, irregular acanthosis, and focal liquefaction degeneration of the basal cell layer. Wispy strands of bluish materials between collagen bundles could be found in the papillary and reticular dermis (Figure 1B and C). The bluish materials showed positive staining for Alcian blue—an indicator of acidic mucins and mucopolysaccharides (Figure 2). Based on the clinical and histopathologic manifestations, a diagnosis of mucinous nevus was established.
Mucinous nevus is a rare, primary cutaneous mucinosis that predominantly presents in childhood or adolescence and is most commonly seen in males. Adult onset of the disease has rarely been reported.1,2 It is characterized by skin-colored to brownish papules, nodules, or plaques arranged in a unilateral, linear, zosteriform, grouped, or dermatomal manner.2 One histopathologic hallmark of the disease is a diffuse or bandlike deposition of mucin between collagen fibers in the superficial dermis with or without combined epidermal nevuslike changes.2 Electron microscopy reveals excessive mucin and hyperactive fibroblasts with increased rough endoplasmic reticulum and secretory vacuoles in the lesional regions compared with perilesional regions. However, increased fibroblasts are not seen in the lesions.1
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Corresponding Author: Yue-Ping Zeng, MD, Department of Dermatology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, No.1, Shuaifuyuan, Dongcheng District, Beijing 100730, China (firstname.lastname@example.org).
Published Online: April 28, 2021. doi:10.1001/jamadermatol.2021.0444
Conflict of Interest Disclosures: None reported.
Additional Contributions: We thank the patient for granting permission to publish this information.
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