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During the coronavirus disease 2019 (COVID‐19) pandemic, COVID‐19 vaccines were administered worldwide. A number of skin reactions, including primary cutaneous T‐cell lymphoproliferative disorders (LPDs) were reported following COVID‐19 vaccination. We report a case of primary cutaneous marginal zone lymphoproliferative disorder (PCMZLPD) secondary to COVID‐19 vaccination. A 57‐year‐old man presented with an erythematous nodule on his left arm at the site of vaccine inoculation following his first dose of the Moderna (mRNA‐1273) vaccine a few weeks prior. The nodule continued to progress in size after the second dose. A skin biopsy specimen of the nodule showed a diffuse dermal infiltrate of small to medium‐sized lymphocytes with plasma cells and histiocytes. The infiltrate was composed of CD3+ T cells with CD20+ and CD79a+ B cells. The neoplastic B cells reacted with BCL‐2 and were negative for BCL‐6 and CD10. Kappa light chain restriction was identified by in situ hybridization. Gene rearrangement studies revealed kappa light chain monoclonality, confirming the diagnosis of PCMZLPD. The temporal association with the Moderna vaccination and the occurrence of the lesion at the inoculation site indicate a COVID‐19 vaccination‐induced PCMZLPD. This is one of the rare cases of PCMZLPD following COVID‐19 vaccination. [ABSTRACT FROM AUTHOR]

Dowling‐Degos disease is a rare autosomal dominant genodermatosis. It is characterized by acquired reticulate hyperpigmentation over the flexures, comedone‐like follicular papules, and pitted perioral scars that usually develop during adulthood. Mutations in genes affecting melanosome transfer, and melanocyte and keratinocyte differentiation have been implicated in the pathogenesis of this disease. These genes include KRT5, POFUT1, POGLUT1 and, most recently, PSENEN. Dowling‐Degos disease can be found in isolation or with other associated findings, most notably hidradenitis suppurativa. This condition belongs to a spectrum of conditions that all result in reticulate hyperpigmentation that at times are hard to distinguish from each other. The most closely linked entity is Galli‐Galli, which is clinically indistinguishable from Dowling‐Degos disease and can only be distinguished by the presence of acantholysis on microscopy. Unfortunately, Dowling‐Degos disease is generally progressive and recalcitrant to treatment. [ABSTRACT FROM AUTHOR]

Retinoids are a class of compounds derived from vitamin A or having structural and/or functional similarities with vitamin A. They are classified into three generations based on their molecular structures. Inside the body, retinoids bind to several classes of proteins including retinoid-binding proteins and retinoid nuclear receptors. This eventually leads to the activation of specific regulatory regions of DNA – called the retinoic acid response elements – involved in regulating cell growth, differentiation and apoptosis. Several clinical trials have studied the role of topical and systemic retinoids in disease, and research is still ongoing. Currently, retinoids are used in several fields of medicine. This paper aims to review the structure, mechanisms of action, and adverse effects of retinoids, as well as some of their current uses in Dermatology. [ABSTRACT FROM AUTHOR]

We should also keep in mind that MRS should now be added to the differential diagnosis of entities that may exhibit perineural granulomatous inflammation including leprosy and sarcoidosis. For example, perineural inflammation in cutaneous sarcoidosis has been linked to some of the neurologic manifestations encountered such as sensory disturbances.4 The same has been demonstrated in leprosy whereby the perineural inflammation may cause injury and subsequent neurologic symptoms.5 In addition, we also want to highlight the authors' significant finding at the diagnostic level. We recently read with great interest the article: "The histopathological spectrum of Melkersson-Rosenthal syndrome: Analysis of 47 cases".1 In this study, the authors describe the histopathological findings of oral lesions of patients with Melkersson-Rosenthal syndrome (MRS). [Extracted from the article]

Competing Interests: The authors declare no conflicts of interest.