Dear Editor, Bullous pemphigoid (BP) is an autoimmune disease that tends to occur in elderly individuals. Here, we report a case that developed BP after receiving the second dose of coronavirus disease 19 (COVID-19) vaccine. The patient, an 83-year-old Japanese woman with bipolar disorder, was treated for xerotic eczema in a clinic and her eczema was relieved with topical steroids. Three days after receiving the second dose of tozinameran, the BNT162b2 mRNA COVID-19 vaccine, F I G U R E 1 (a,b) Histopathological images (hematoxylin-eosin). (a) Subepidermal bulla (original magnification ×5) and (b) vacuolar degeneration at the epidermis−dermis junction with eosinophilic infiltration (×100). (c) Direct immunofluorescence showed the linear deposition of immunoglobulin G at the basement membrane zone. (d,e) Clinical images. (d) Diffuse erythema and erosion and (e) blisters

Secondary extramammary Paget disease (s‐EMPD) represents anal canal and rectal, bladder, and gynecological cancers, which horizontally extend within the epidermis of the anal and vulvar skin. It is necessary to distinguish this condition from primary extramammary Paget disease (p‐EMPD), which occurs primarily in genital and perianal areas. This study aimed to investigate the clinical and histopathological features of these two conditions in the perianal skin and to identify useful features for differentiation. We retrospectively analyzed 16 patients who visited Shinshu University Hospital from 2009 to 2022 and presented with perianal skin lesions and suspected EMPD. Six patients had p‐EMPD and 10 had s‐EMPD derived from anal canal adenocarcinoma. Regarding clinical features, nine of 10 (90%) of the s‐EMPD cases had symmetric skin lesions, whereas all of the p‐EMPD cases had asymmetrical lesions (p = 0.0004). Furthermore, assessment of symmetry around the anus showed that s‐EMPD had a significantly smaller coefficient of variation than p‐EMPD (0.35 and 0.62, respectively; p = 0.048), suggesting that s‐EMPD was more symmetric around the anus. The frequency of raised lesions, such as foci or nodules, was nine of 10 (90%) for s‐EMPD and one of six (16%) for p‐EMPD (p = 0.003). Well‐defined tumor borders on the lateral margins were identified in s‐EMPD (5/10, 50%); however, they were not identified in p‐EMPD (0/6, 0%). The borders tended to be clearer in s‐EMPD; however, the difference was not significant (p = 0.078). Based on these findings, we recommend consideration of s‐EMPD when anal skin lesions are symmetrical, well‐defined, or raised.