Lichen planus pemphigoides (LPP) is a rare autoimmune subepidermal disease that can occur in patients receiving immune checkpoint inhibitors. Its clinical manifestations are combined with the characteristics of lichen planus with bullous pemphigoid that can occur on either skin or oral mucosa. It should be noted that oral LPP is very rare. Here, we report a novel case of oral LPP induced by an anti-PD-1 agent. The patient presented with typical clinical features in oral mucosa, and the diagnosis was based on histopathology and immunological studies. Given that the patient was receiving an anti-PD-1 agent, topical therapy was chosen, and a nice therapeutic effect was obtained. No significant recurrence was observed after a 2-year follow-up. A good and stable therapeutic effect achieved by rapid and local symptomatic medication suggests that accurate and sensitive diagnosis is necessary.

As dermatopathologists, we routinely diagnose melanocytic nevi, melanomas, and occasionally melanocytomas in our daily clinical practice. However, it is now clearly established that the presence of melanocytic differentiation in a tumor does not necessarily indicate any of the aforementioned diagnoses. Tumors such as clear cell sarcoma, malignant melanotic nerve sheath tumor, PEComa, melanotic neuroectodermic tumor of infancy, and even certain translocation-associated renal cell carcinomas all share the common characteristic of melanin synthesis. Over the past two decades, with the advent of molecular diagnostics, there has been an explosion of new data and discoveries in this field. Examples such as CRTC1::TRIM11 cutaneous tumors and MITF pathway-activated melanocytic tumors (ACTIN::MITF and MITF::CREM) have been incorporated into the latest edition of the WHO classification of skin tumors (5th ed). In a recent issue, Alexandrescu et al. reported another case of a dermal/subcutaneous melanocytic tumor harboring a MITF::CREM1 translocation. In a separate paper within the current issue, Li et al. present a case of clear cell sarcoma with the rare EWSR1::CREM fusion, which had initially been misdiagnosed as melanoma with regional and distant metastases. We warmly welcome these two very interesting and high-quality articles to our journal, and we eagerly anticipate what the future holds for this fascinating category of tumors.

Livedoid vasculopathy (LV) is characterized by fibrin deposition and thrombosis in the small vessels of the superficial dermis. It is widely recognized as an occlusive disease, which is primarily treated with anticoagulation therapy. We retrospectively analyzed the clinical and histopathological characteristics of patients diagnosed with LV at a tertiary dermatology department to explore the characteristics of lymphocytic vasculitis in LV. The frequency of vasculitis and the types of vessels involved were examined based on the diameters and elastic fiber distribution of the involved vessels. In addition, the immunophenotypes of infiltrating lymphocytes were analyzed. In a large retrospective series including 358 LV cases, we identified 137 (38.3%) cases of lymphocytic vasculitis. Among them, 48 cases involved medium-sized vessels, including arterioles and venules, whereas 89 cases involved only small vessels. In addition, 12 cases displayed a segmental distribution of vasculitis. The infiltrating lymphocytes were mainly T cells, with dominant cells stained positive for CD4. Lymphocytic vasculitis forms part of the histological spectrum of LV, affecting both medium-sized and small vessels. It is possible that the occlusion of small vessels may represent a phenomenon secondary to lymphocytic vasculitis.

Perforating lichen nitidus is a rare subtype of lichen nitidus, with approximately 11 cases reported worldwide. Lesions typically present in young male patients at sites prone to mechanical irritation, including the hands, feet, forearms, elbows, and knees. Classic histopathologic features of perforating lichen nitidus show a lymphohistiocytic infiltrate within the papillary dermis between hyperplastic rete ridges with transepidermal elimination of dermal contents. Very few cases are reported in the literature of lichen nitidus and its association with atopic dermatitis. This is the first case describing perforating lichen nitidus in a patient with a history of atopic dermatitis being treated with dupilumab injections. Lesions of perforating lichen nitidus worsened with successful treatment of atopic dermatitis. These findings suggest a unique pathophysiology of perforating lichen nitidus lesions.

Desmoplastic melanoma (DM), a type of spindle cell melanoma separated into pure desmoplastic melanoma (PDM) and mixed desmoplastic melanoma (MDM) subtypes, can be a diagnostic challenge and easily confused for dermal scar, especially PDM. We report a 65-year-old white man who received a left thumb amputation after an initial biopsy for melanoma, an unclassified type with epithelioid morphology. The amputation and sentinel lymph node specimens were significant for residual melanoma with epithelioid morphology, dermal scar, and a slightly expanded "scar-like" capsular area in one of seven lymph nodes, which was diffusely positive for SOX10 on reflex sentinel lymph node immunohistochemical protocol. On re-review of the amputation "scar" like area, a subsequent SOX10 stain confirmed the diagnosis of MDM in this area with epithelioid and spindle cell morphology, significantly upgrading the tumor stage. We share this case to highlight: (i) MDM, although exceptionally uncommon, can result in a pure spindle cell lymph node metastasis, (ii) to encourage increased utilization of SOX10 to assess sentinel lymph node biopsies, especially in the context of melanomas with a spindle cell component, and (iii) share an example of inattentional blindness which was fortunately identified by reflex sentinel lymph node immunohistochemical protocols.

Imipramine is a tricyclic antidepressant typically reserved for patients with treatment-resistant mood disorders. A rare side effect of long-term use of imipramine is a slowly progressive melanin-associated, slate gray-blue hyperpigmentation of the skin in a photo-distributed pattern. We report a case of imipramine-induced hyperpigmentation developing 50 years after initiating imipramine therapy, whose lesions were essentially devoid of melanin on histopathological exam. This differs from all other reported cases of imipramine-induced hyperpigmentation in two notable respects. First, the time between initiating imipramine therapy and the onset of pigmentation changes was nearly 30 years longer than prior case reports. Second, the lack of melanin in our samples suggests a divergence from the hypothesized melanin-imipramine complex mechanism of hyperpigmentation. Instead, we propose a novel pathogenesis of imipramine-induced hyperpigmentation that is unrelated to melanin.

AbstractIntroductionWhile most melanocytic neoplasms can be classified as either benign or malignant by histopathology alone, ancillary molecular diagnostic tests can be necessary to establish the correct diagnosis in challenging cases. Currently, the detection of copy number variations (CNVs) by fluorescence in situ hybridization and chromosomal microarray (CMA) are the most popular methods, but remain expensive and inaccessible. We aim to develop a relatively inexpensive, fast, and accessible molecular assay to detect CNVs relevant to melanoma using droplet digital polymerase chain reaction (ddPCR) technology.MethodsIn this proof‐of‐concept study, we evaluated CNVs in MYC and MYB genes from 73 cases of benign nevi, borderline melanocytic lesions, and primary and metastatic melanoma at our institution from 2015 to 2022. A multiplexed ddPCR assay and CMA were performed on each sample, and the results were compared.ResultsConcordance analysis of ddPCR with CMA for quantification of MYC and MYB CNVs revealed a sensitivity and specificity of 89% and 86% for MYC and 83% and 74% for MYB, respectively.ConclusionWe demonstrate the first use of a multiplexed ddPCR assay to identify CNVs in melanocytic neoplasms. With further improvement and validation, ddPCR may represent a low‐cost and rapid tool to aid in the diagnosis of histopathologically ambiguous melanocytic tumors.

CD30+ cells are typically part of lymphoproliferative disorders but can also be seen in inflammatory dermatoses. We present a case of 47-year-old man with a history of B-lymphoblastic leukemia (B-ALL) who presented with fever, leukocytosis, and papulonodular skin lesions, involving the extremities and trunk. A punch biopsy specimen demonstrated papillary dermal edema with a neutrophilic and histiocytic infiltrate extending into the subcutis. The infiltrate also harbored scattered large cells that were positive for CD30 and demonstrated the immunohistochemical profile of monocytes. A diagnosis of histiocytoid Sweet syndrome with CD30+ cells was made. The case is unique, demonstrating a combination of Sweet syndrome variants with subcutis involvement, histiocytoid morphology, and large CD30+ cells. A prior history of B-ALL and immunohistochemical profile of monocytes with immature morphology broadened the differential diagnosis and added to the diagnostic challenge.