Background Cutaneous reactions, mostly on injection site after mRNA‐based COVID‐19 vaccines, have been reported but not with detailed histopathological characterization. Objectives Characterization and classification of these reactions in a clinical and pathological point of view. Methods Monocentric case series of 11 patients with cutaneous manifestations, clinically and histologically characterized after COVID‐19 vaccination. Results From January to June 2021, we recorded 11 cutaneous reactions to mRNA COVID‐19 vaccines from BNT162b2 (n = 8) and mRNA‐1273 (n = 3). Generalized reactions showing erythematous rash or purpura were the most common clinical presentation, and drug‐reaction‐like pattern was the most common histological finding. Conclusions A proper clinicopathological classification will be helpful in the early diagnosis and management of the cutaneous reactions to mRNA COVID‐19 vaccines.

Background: Hyaluronidases are essential for the breakdown of hyaluronate (HA) in tissues and may be used to prevent the adverse effects of HA fillers. Objectives: We explored the effect of hyaluronidase on exogenous and endogenous HA in vitro and in vivo. Materials and Methods: HA fillers were incubated with different concentrations of hyaluronidase and visualized by electrophoresis. HA fillers were injected in the skin of hairless mice, and 4 h later hyaluronidase was injected in the papules of exogenous HA. Hyaluronidase was injected in the nodule of pretibial myxedema of a male patient with Graves' disease. Skin sections of mice and of the patient were performed, and a skin ultrasound system was used to monitor the evolution of skin lesions. Results: Hyaluronidase showed a degrading effect on HA with increasing concentrations. Hyaluronidase injection significantly decreased the content of exogenous HA within 3 days. Intralesional injection of hyaluronidase resulted in dissolution of the nodule of pretibial myxedema with no recurrence during 3 months. Conclusion. These results show that the injection of hyaluronidase is capable of degrading exogenous HA in mouse skin and endogenous HA in human skin in vivo and may be a therapeutic option for skin diseases characterized by abnormal accumulation of HA.

Introduction: Pityriasis lichenoides (PL) is an infrequent skin disorder. The clinical manifestations are usually specific enough for a reliable diagnosis, although the histopathological assessment of a biopsy is sometimes needed to differentiate between PL and a range of other diseases. The objectives of this study were to review cases of PL managed in our hospital, confirm the classical histopathological features of PL, and identify signs that may be of value in the diagnosis of PL. Materials and Methods: All cases of PL assessed in our pathology department between January 2007 and December 2017 were retrieved, and all slides were reviewed. Cases were selected only if a diagnosis of PL was initially suggested by a dermatologist and then confirmed by the histopathological assessment. Results: Seventy-one cases met the study criteria. The following features were almost always present: vacuolar changes or necrotic keratinocytes (100%), both superficial and deep lymphocytic infiltrates (99%), and the infiltration of lymphocytes into the adnexal epithelium (97%). The inflammatory cells were always small- to medium-sized lymphocytes. There were no eosinophilic infiltrates. Superficial perivascular and/or intraepidermal red blood cells were observed in 83% of cases. Discussion: We highlighted the presence of a deep dermal lymphocytic infiltrate, with a “T-shaped” periadnexal arrangement along the full length of the follicular and sudoral epithelia. This might be a feature that enables the differentiation of PL from other diseases. Our findings also prompted a number of physiopathological hypotheses for PL. Conclusions: Our present results confirmed the classical histological aspects of PL and provided some useful new diagnostic features.

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Rhizomucor pusillus is an opportunistic fungus that causes infections (mucormycosis) in patients with a predisposing disease, such as diabetes mellitus and immunodeficiency. Classic manifestations are sinus, pulmonary, and skin infections. Skin lesions consist of tender, erythematous, indurated, and necrotic plaques. The diagnosis is made by identification of the organisms by histopathological analysis of the lesion, showing nonseptate fungal hyphae in the dermis and invasion of the vessel walls, or by means of cultures. Amphotericin B and surgery are the treatments of choice.