Bar code reader - an algorithmic approach to cutaneous occluding vasculopathies? Part I: small vessel vasculopathies

Vasculitides and occluding vasculopathies, challenges in recognizing histopathological patterns, and their solutions

In this review, we propose a classification of vasculitides and occluding vasculopathies using the clinicopathological correlation as the basic process. We use an algorithmic approach with pattern analysis, which allows reliable reporting of microscopic findings. We first differentiate between small and medium vessel vasculitis. Second, we differentiate the subtypes of small- and medium-sized vessels. Finally, we differentiate vasculitides according to the predominant cell type into leukocytoclastic and/or granulomatous vasculitis. Regarding leukocytoclastic vasculitis as a central reaction pattern of cutaneous small/medium vessel vasculitides, its relation or variations may be arranged in a wheel-like order. With respect to occluding vasculopathies, the first two steps are identical to the algorithm of vasculitides, and we finally differentiate according to the time point of the coagulation/reorganization process and the involved inflammatory cells/stromal features. By visualizing the criteria in the style of bar codes, clinical and histological overlaps and differences may become more transparent.

Livedoid vasculopathy: A review with focus on terminology and pathogenesis

Livedoid vasculopathy (LV) is a rare thrombotic vasculopathy of the dermis characterized by painful, relapsing ulcers over the lower extremities. Diagnosis is challenging due to the overlap in clinical appearance and nomenclature with other skin disorders. Treatment selection is complicated by poor understanding of the pathogenesis of LV and lack of robust clinical trials evaluating therapy efficacy. The terminology and pathophysiology of LV are reviewed here, along with its epidemiology, clinical and histologic features, and treatment options. A diagnostic pathway is suggested to guide providers in evaluating for comorbidities, referring to appropriate specialists, and choosing from the available classes of therapy.

Single-cell transcriptome profiling reveals vascular endothelial cell heterogeneity in human skin

Vascular endothelial cells (ECs) are increasingly recognized as active players in intercellular crosstalk more than passive linings of a conduit for nutrition delivery. Yet, their functional roles and heterogeneity in skin remain uncharacterized. We have used single-cell RNA sequencing (scRNA-seq) as a profiling strategy to investigate the tissue-specific features and intra-tissue heterogeneity in dermal ECs at single-cell level.

Methods: Skin tissues collected from 10 donors were subjected to scRNA-seq. Human dermal EC atlas of over 23,000 single-cell transcriptomes was obtained and further analyzed. Arteriovenous markers discovered in scRNA-seq were validated in human skin samples via immunofluorescence. To illustrate tissue-specific characteristics of dermal ECs, ECs from other human tissues were extracted from previously reported data and compared with our transcriptomic data.

Results: In comparison with ECs from other human tissues, dermal ECs possess unique characteristics in metabolism, cytokine signaling, chemotaxis, and cell adhesions. Within dermal ECs, 5 major subtypes were identified, which varied in molecular signatures and biological activities. Metabolic transcriptome analysis revealed a preference for oxidative phosphorylation in arteriole ECs when compared to capillary and venule ECs. Capillary ECs abundantly expressed HLA-II molecules, suggesting its immune-surveillance role. Post-capillary venule ECs, with high levels of adhesion molecules, were equipped with the capacity in immune cell arrest, adhesion, and infiltration.

Conclusion: Our study provides a comprehensive characterization of EC features and heterogeneity in human dermis and sets the stage for future research in identifying disease-specific alterations of dermal ECs in various dermatoses.

Bar Code Reader - an algorithmic approach to cutaneous occluding vasculopathies? part II medium vessel vasculopathies

Aims

Classifications of occluding vasculopathies (except vasculitis [1]) may exhibit some difficulties. Firstly, classifications may follow different principles, e.g. clinicopathologic findings, etiology or pathogenesis. Secondly, authors may not distinguish between vasculitis and occluding vasculopathies. Thirdly, occluding vasculopathies are systemic diseases. Organ‐specific variations make morphologic findings difficult to compare. Moreover, subtle changes are recognized in the skin, but may be invisible in other organs. Our aim was to use the skin and subcutis as a tool and clinicopathological correlation as the basic process for classification.

Methods and results

We first differentiate in the skin between small and medium vessel occluding vasculopathies. Here we focus on medium vessel‐occluding vasculopathies. In the second step we differentiate the vessel subtypes. In the final step, we differentiate according to the time point of the coagulation/reorganization process and the involved inflammatory cells/stromal features. By applying the same procedure to the various entities and visualizing the findings in the style of bar codes, the overlaps and differences in the clinical picture as well as the histopathology become more apparent.

Conclusions

Occluding vasculopathies are often not separate entities, but reaction patterns and epiphenomena. Distinguishing them from vasculitides is crucial because of the differences in pathogenesis, therapeutic approach and prognosis.