Primary Extramammary Paget Disease of the Perineum Mimicking Chronic Dermatitis: A Case Report.

INTRODUCTION: Extramammary Paget's disease (EMPD) is a rare cutaneous adenocarcinoma that typically arises in apocrine gland-rich areas of the skin (genital, perianal, axillary regions) of older adults. Clinically, it often presents as a chronic eczematous or pruritic plaque that can be mistaken for benign dermatoses. CASE REPORT: We report a 65-year-old postmenopausal woman with a 3-year history of a slowly expanding, itchy perineal plaque. The lesion was initially misdiagnosed as dermatitis and treated unsuccessfully with topical steroids, antifungals, and antibiotics. Examination revealed an indurated, verrucous plaque on the perineum with areas of flesh-colored, hypopigmented, and violaceous discoloration. There were no lymphadenopathy or other lesions. A punch biopsy showed epidermal hyperkeratosis and acanthosis with scattered pagetoid cells (large pale pleomorphic cells with atypical nuclei and mitoses) throughout the epidermis. Immunohistochemistry demonstrated tumor cell positivity for cytokeratin 7 (CK7), carcinoembryonic antigen (CEA), gross cystic disease fluid protein-15 (GCDFP-15), and HER2, consistent with primary EMPD. Metastatic workup, including pelvic MRI and colonoscopy, revealed no underlying internal malignancy. The patient underwent wide local excision with clear margins. CONCLUSION: This case highlights the importance of considering EMPD in chronic refractory anogenital dermatoses of the elderly. The CARE checklist was utilized in the writing of this case. Early skin biopsy and histopathologic examination are crucial for diagnosis. Definitive treatment with surgical excision offers the best chance for cure, and thorough evaluation for underlying carcinoma is essential in guiding management and follow-up.