Preferentially expressed Antigen in MElanoma immunohistochemistry as an adjunct for evaluating ambiguous melanocytic proliferation.

The histopathological assessment of diagnostically ambiguous melanocytic proliferation remains one of the biggest challenges in the dermatopathology field. Preferentially expressed Antigen in MElanoma (PRAME) immunostaining has been shown highly specific for distinguishing unequivocal malignant melanocytic proliferation from benign ones. Knowledge on its utility for evaluating ambiguous melanocytic neoplasms remains limited. We retrieved in our institutional database all cases of diagnostically ambiguous melanocytic neoplasms from January 2016 to January 2021. Each case was subclassified into "favor benign" or "favor malignant" neoplasm using all collected data. Immunohistochemical expression of PRAME was assessed and correlated with the final subclassification. Using a previously proposed scoring system, diffuse immunopositivity (>75% of tumor cells) was considered positive. Furthermore, for ambiguous melanocytic proliferation occurring on a pre-existing nevus, the staining was considered positive if more than 75% of the morphologically atypical neoplastic cells were labeled, excluding morphologically unambiguous benign nevocytes. Fifty-five cases of ambiguous melanocytic proliferation were examined. Thirty-one cases were finally subclassified as "favor malignant" neoplasms and 24 as "favor benign" neoplasms. Thirty-one tumors showed immunopositivity for PRAME, representing, respectively, 8.3% and 93.5% of "favor benign" and "favor malignant" neoplasms. The specificity and sensitivity of PRAME immunohistochemistry for benign/malignant distinction were, respectively, 91.7% and 93.5%.PRAME IHC shows high sensitivity and specificity for distinguishing malignant challenging melanocytic proliferations from benign ones and could be used as an everyday tool. However, PRAME immunoreactivity should be interpreted cautiously, knowing that rare benign melanocytic neoplasms could show diffuse positivity.

Cutaneous manifestations in patients with coronavirus disease 2019: clinical and histological findings.

The clinical spectrum of coronavirus disease 2019 is getting wider with the exponential increase of patients worldwide. Initially described with flu-like symptoms, variable cutaneous manifestations have been reported, with only few histopathological descriptions. Detection of the virus in cutaneous samples has been assessed in very few cases until now, and the causative role of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has not been proven for every type of cutaneous manifestations yet. We aimed to describe histological features of cutaneous eruptions occurring concomitantly to SARS-CoV-2 infection and assess by immunochemistry and in situ hybridization using RNAscope validation techniques the presence of the virus in skin lesions. We retrieved all skin biopsies received in the departments of pathology and dermatopathology, University Hospital of Strasbourg, performed in hospitalized SARS-CoV-2-infected patients presenting concomitant cutaneous manifestations since March 2020. In situ hybridization and immunostaining using a polyclonal SARS nucleocapsid protein antibody were performed on each sample. Skin biopsies from six patients presenting morbilliform eruption concomitant to SARS-CoV-2 infection were available for evaluation. All six samples showed varying degrees of spongiosis, perivascular inflammatory infiltrates of the dermis, and, for some of them, discrete interface dermatitis. In situ hybridization and immunohistochemistry were negative in all cutaneous samples. Morbilliform rash concomitant to SARS-CoV-2 infection is characterized by mild and unspecific histopathological features with no detectable viral RNA and protein and appears then not to be directly caused by the virus. Even if, at least for a few cases, the differential diagnosis with drug hypersensitivity reaction can be difficult, these cutaneous eruptions seem to rather correspond to paraviral rashes.

Intralymphatic CD30+ T-cell proliferation during DRESS: a mimic of intravascular lymphoma.

INTRODUCTION: We describe the case of a patient presenting with drug rash with eosinophilia and systemic symptoms (DRESS), where cutaneous biopsy revealed intravascular atypical lymphocytes suggestive of lymphoma. CASE REPORT: A 77-year-old man was treated with antibiotics for a hip prosthesis infection. Eight weeks later, he developed a maculo-papulous eruption, edema of the extremities, fever and blood eosinophilia. Cutaneous biopsy revealed an atypical T-cell proliferation into the dermal lymphatic vessels. The lymphocytes were mid-sized, with mitoses and apoptotic figures. They were CD3+, CD4+, CD5+ and some were CD30+. There was no T-cell receptor (TcR) clonal rearrangement. Complete regression of cutaneous eruption and eosinophilia was observed after ceasing treatment with antibiotics. The diagnosis was that of a benign atypical intralymphatic T-cell proliferation associated with DRESS. DISCUSSION: The occurrence of atypical dermal CD30+ T-cells in cutaneous biopsy during benign reactive conditions such as arthropod bites or scabies is well-known. The intralymphatic localization of such atypical reactive lymphocytes is much less common and represents a diagnostic pitfall because it can suggest aggressive intravascular lymphoma. CONCLUSION: We report the first case of benign atypical intralymphatic CD30+ T-cell proliferation associated with DRESS. Diagnostic clues include immunohistochemistry, absence of TcR clonal rearrangement, and anatomo-clinical correlation.