Lichen planus (LP) is a chronic inflammatory disorder involving the skin or mucous membranes. Previous studies have demonstrated that some LP patients showed positive enzyme-linked immunosorbent assay (ELISA) for desmoglein (DSG) antibodies. We report a case with intractable painful oral lesions. ELISA indices for DSG1 and 3 antibodies were increased by 49 and 36, respectively. Histopathological analysis revealed irregular acanthosis and band-like infiltration of lymphocytes at the dermal-epidermal interface. Direct immunofluorescence revealed negative deposits of immunoglobulin G and C3 in intracellular spaces of the epidermis. Indirect immunofluorescence of normal skin also did not detect any antibodies. Consequently, we made a final diagnosis of oral LP. The previous two LP cases with positive ELISA for DSG antibodies and our case manifested the erosive form, the most advanced oral LP. Therefore, it is a possibility that severe damage of keratinocytes may induce generation of DSG antibodies. However, negative results of immunofluorescence and no relation between disease severity and titers of antibodies make the possibility unlikely. We should measure titers of DSG antibodies in LP patients and accumulate data to establish a valid conclusion.

We report a case of dermoid cysts on the right lateral eyebrow and anterior neck. Multiple concurrent dermoid cysts, as in the present case, are very rare. The differential diagnosis of dermoid cyst includes epidermoid (epidermal inclusion) cyst, trichilemmal cyst, pilomatrixoma, lymphatic malformation, and lipoma. In particular, thyroglossal duct cyst and midline anterior neck inclusion cyst are part of the differential diagnosis when the lesion is in the anterior neck.

The palmoplantar keratodermas (PPKs) are a large group of genodermatoses comprising nearly 60 genetically distinct diseases. They are characterized by hyperkeratosis on the palms and soles with or without extrapalmoplantar hyperkeratotic lesions. Focal PPK is one of the hallmarks of pachyonychia congenita, a rare autosomal dominant disorder resulting from mutations in the keratin genes KRT6A, KRT6B, KRT16 or KRT17. Recently, in-frame deletion mutations of KRT6C have been identified in three families with focal PPK with slight or no nail changes. We report here a novel KRT6C mutation identified in a Japanese family with PPK with phenotypic heterogeneity, presenting with not only focal but also diffuse hyperkeratosis. The proband had diffuse hyperkeratosis on the soles and small focal hyperkeratoses on the palms, while the two other affected individuals showed focal hyperkeratoses on the soles. All three patients were heterozygotes for c.1414G>A in KRT6C, predicted to result in p.Glu472Lys. These findings strongly suggest that screening of patients with nonepidermolytic diffuse PPK, in whom the pathogenic mutations are yet to be determined, might identify mutations in KRT6C.

Impetigo herpetiformis (IH) is a rare variant of generalized pustular psoriasis (GPP), which develops during pregnancy. GPP is associated with mutations of IL36RN, but it is still unclear whether the same is true of IH. A 20-year-old Japanese woman developed erythema and pustules on her trunk during the 27th week of her first pregnancy.

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Primary rhabdoid melanoma (PRM) is a rare variant of melanoma. Herein, we describe a case of primary amelanotic rhabdoid melanoma and review the clinicopathological features of previously reported cases of PRMs. A 63-year-old Japanese man presented with a nonpigmented red granular tumor without peripheral pigmented macules on the left heel measuring 21 × 18 mm in size. Light microscopic examination revealed a tumor mass composed entirely of polygonal neoplastic cells resembling pulmonary alveoli. Tumor cells were also discohesive with bizarre nuclei, prominent nucleoli and large hyaline cytoplasmic inclusions. No melanin pigment was present. Tumor cells were strongly and diffusely positive for S-100, MART-1, HMB-45 and vimentin, while negative for desmin, αSMA and synaptophysin. According to previous reviews, PRM tends to be amelanotic and nodular. S-100 protein and vimentin stained in all cases contrary to low stainability for HMB-45, which was, by contrast, positive in our case. Prognosis of PRM remains controversial due to the very rare occurrence of this tumor and the small number of confirmed cases that have been reported. Recognition of this rare entity is important in clinical practice even for skillful dermatologists to avoid misdiagnosis with the other tumors and to determinate the subsequent treatment principles.

Drug‐induced hypersensitivity syndrome (DiHS) is a severe drug eruption that can induce reactivation of herpesviruses such as human herpesvirus 6, resulting in symptom flare‐up and organ damage. DiHS is known as drug reaction with eosinophilia and systemic symptoms (DRESS) in Europe. We report three cases of DiHS that could have been triggered by mRNA‐based coronavirus disease 2019 (COVID‐19) vaccines. In these three patients, symptoms of DiHS developed 2–6 days after the first dose of an mRNA‐based COVID‐19 vaccine. Although there have been no reports of DiHS/DRESS induced by mRNA‐based COVID‐19 vaccines in domestic and international journals despite the progress in vaccination worldwide, we speculate that mRNA‐based COVID‐19 vaccines might have triggered the development of DiHS/DRESS in our patients. In the current coronavirus epidemic, it might be important to assess mRNA‐based COVID‐19 vaccination status and date of vaccination when evaluating a patient with DiHS/DRESS.