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Photoplethysmography (PPG) devices are widely used in clinical practice but the origin of PPG signal is still under debating. The classical theory assumes that the PPG waveform stems from variations of blood volume in pulsating arteries. In this research we analysed high-speed video recordings of capillaries in a fingernail bed. It was found that speed of erythrocytes in capillaries has pronounced modulation in time, which follows variations of instantaneous blood pressure in arteries. However, the mean speed significantly differs even for neighbour capillaries whereas change of the speed occurs in phase for the most of capillaries. Moreover, the light intensity remitted from the papillary dermis is also modulated at the heartbeat frequency displaying significant correlation with waveforms of the RBC speed. Obtained results can hardly be explained by the classical theory of PPG signal formation. Shallow penetrating visible light acquires modulation of erythrocytes density in the capillary bed without interacting with deeper situated pulsating arteries. Therefore, the capillary bed could serve as a distributed sensor for monitor the status of deep vessels. Better understanding of the photoplethysmography basis will result in a wider range of applications of this fast growing technology in both medical and research practice.

ObjectiveTo assess microvascular changes in nailfold capillaries in patients with systemic sclerosis-associated interstitial lung disease (SSc-ILD) who received nintedanib or placebo in a sub-study of the SENSCIS trial.MethodsNailfold capillaroscopy (NC) was performed at baseline and week 52. In the nintedanib and placebo groups, we measured capillary density (number of capillaries/mm), giant capillaries, abnormal shapes and percentage of fingers with microhaemorrhages. In addition, capillary density was evaluated in patients who did/did not have risk factors for rapid forced vital capacity (FVC) decline at baseline and who did/did not have ILD progression (absolute decline in FVC % predicted >5% or death) from baseline to week 52.ResultsBetween baseline and week 52, no notable changes were observed in any NC measurement in the overall placebo or nintedanib groups. In patients with risk factors for rapid FVC decline (n=38), there was a numerical reduction in mean capillary density over 52 weeks with placebo, but it remained stable with nintedanib. Among patients who had ILD progression (n=11), there was a numerical increase in mean capillary density over 52 weeks with nintedanib, but it remained stable with placebo. There were no notable changes in capillary density among patients who did not have risk factors for rapid FVC decline at baseline or ILD progression at week 52.ConclusionIn a substudy of the SENSCIS trial, numerical differences in changes in capillary density assessed by NC over 52 weeks may suggest a potential effect of nintedanib in patients at risk of ILD progression.

Nailfold capillaroscopy (NFC) is a reproducible, simple, low-cost, and safe imaging technique used for morphological analysis of nail bed capillaries. It is considered to be extremely useful for the investigation of Raynaud’s phenomenon and for the early diagnosis of systemic sclerosis (SSc). The capillaroscopic pattern typically associated with SSc, scleroderma (“SD”) pattern, is characterized by dilated capillaries, microhemorrhages, avascular areas and/or capillary loss, and distortion of the capillary architecture. The aim of these recommendations is to provide orientation regarding the relevance of NFC, and to establish a consensus on the indications, nomenclature, the interpretation of NFC findings and the technical equipments that should be used. These recommendations were formulated based on a systematic literature review of studies included in the database MEDLINE (PubMed) without any time restriction.

Endothelial and vascular damage are main leading disability in systemic sclerosis (SSc). Raynaud's phenomenon is the early symptom that presents vascular damage. Nailfold capillaroscopy (NFC) is an easily accessible diagnostic tool in secondary Raynaud's phenomenon. Considering the endothelial damage, clinical manifestations, and plasma cytokines was compared with traditionally used NFC parameter for, which to observe the number of capillaries, deletions in 3 mm, apical limb width and the capillary width itself. We hypothesize that a computer-based NFC system can generate a new powerful parameter which predicts the capillary dimension. We investigated the relationship among the plasma endothelin-1 (ET-1), clinical manifestations and quantitative analysis of computerized NFC, and to assess the optimal method in SSc. The level of ET-1 in 60 SSc patients, 30 healthy, and 23 disease controls were measured by enzyme-linked immunosorbent assay (ELISA) kit. We present a significant difference in all parameters of NFC between SSc patients and control groups. ET-1 level was increased in patients with SSc. In SSc group, capillary dimension and loss of capillaries were strongly associated with digital ulceration (p < 0.01) and pulmonary hypertension (p < 0.05). Capillary dimension and ET-1 level was in correlation with skin-hardening grade, and was higher in SSc patients with pulmonary hypertension or digital ulcer. Capillary dimension showed strong correlation with the endothelin-1 in SSc, healthy and disease control groups. (Rs = 0.31/p < 0.05, Rs = 0.82/p < 0.001, Rs = 0.83/p < 0.001). The results suggest that computer-based microscopic analysis of NFC is a useful method that potentially provides information on organ involvement and plasma ET-1. Capillary dimension maybe a powerful parameter possibly applicable in outpatient clinic for assessing SSc patients.

The aim of this study was to assess nailfold capillaroscopic (NC) findings in patients with primary Sjögren’s syndrome (PSS) with and without Raynaud’s phenomenon (RP) as well as in the presence of positive anti-SSA/Ro and anti-SSB/La antibodies. Videocapillaroscopy was performed in 150 patients with PSS. Data collected included demographics, presence of RP, PSS symptoms, antinuclear antibodies, rheumatoid factor, anti-Ro, anti-La, anti-CCP, salivary scintigraphy, labial biopsy, and NC findings. RP was present in 32 % of PSS, keratoconjunctivitis sicca in 91 %, oral xerosis in 93 %, and skin or genital xerosis in 53 %. In patients with positive anti-SSA/Ro (75 %) and positive anti-SSB/La (40 %), NC showed normal findings in 53 % of cases and non-specific in 36 %. In patients with PSS, NC was normal in 51 % of cases and non-specific in 34 %. Scleroderma pattern was found in 14 patients. RP associated with PSS had non-specific capillaroscopy in 40 % of cases ( p  = 0.1). Pericapillary haemorrhages ( p  = 0.06) and capillary thrombosis ( p  = 0.2) were not increased, but more dilated capillaries were detected in 48 % of cases. Patients with positive anti-Ro and/or anti-La have not a distinct NC profile. Patients with RP associated with PSS had more dilated capillaries, but neither pericapillary haemorrhages nor capillary thrombosis was observed.

The purpose of this study is to study and systematize the current knowledge about the role of capillaroscopy in differentiation of primary and secondary Raynaud’s phenomenon (RP) in rheumatic diseases. This method is a review of the literature. Capillaroscopy is of crucial value for diagnosis and differentiation of primary and secondary RP in rheumatic diseases. The appearance of abnormal capillaroscopic pattern inherits high positive predictive value for the development of systemic rheumatic disease. The most specific pattern is found in systemic sclerosis (SSc), so called “scleroderma pattern”, which is characterized by the presence of dilated capillaries, hemorrhages, avascular areas and neoangiogeneis. It is found in more than 90% of patients with overt SSc. Similar changes are found in patients with dermatomyositis, mixed connective tissue disease, undifferentiated connective tissue disease and they are called “scleroderma-like pattern”. Absence of abnormal capillaroscopic findings can be regarded as a diagnostic criterion for primary RP. Inclusion of pathologic capillaroscopic pattern may increase the sensitivity of ACR classification criteria for SSc. In conclusion, capillaroscopy is of crucial importance for the differentiation of primary and secondary RP in rheumatic diseases, and also in differentiation between different forms of connective tissue diseases as well as for their early diagnosis.

Capillaroscopy is a non-invasive and safe technique that allows the detection and quantification of the early microvascular abnormalities that characterize secondary Raynaud's phenomenon. The well-established role of capillaroscopy for the early diagnosis of systemic sclerosis, its inclusion in the classification criteria, combined with its predictive value for clinical complications of the disease and its potential for monitoring disease progression and treatment response, makes nailfold capillaroscopy an important assessment in clinical practice and research. Capillaroscopy provides a unique window into the microcirculation and its application in diseases in which a microvascular component is suspected; it also may provide new insights into their pathophysiology and natural history.

ObjectivesFamilial chilblain lupus is a monogenic form of cutaneous lupus erythematosus caused by loss-of-function mutations in the nucleases TREX1 or SAMHD1. In a family without TREX1 or SAMHD1 mutation, we sought to determine the causative gene and the underlying disease pathology.MethodsExome sequencing was used for disease gene identification. Structural analysis was performed by homology modelling and docking simulations. Type I interferon (IFN) activation was assessed in cells transfected with STING cDNA using an IFN-β reporter and Western blotting. IFN signatures in patient blood in response to tofacitinib treatment were measured by RT-PCR of IFN-stimulated genes.ResultsIn a multigenerational family with five members affected with chilblain lupus, we identified a heterozygous mutation of STING, a signalling molecule in the cytosolic DNA sensing pathway. Structural and functional analyses indicate that mutant STING enhances homodimerisation in the absence of its ligand cGAMP resulting in constitutive type I IFN activation. Treatment of two affected family members with the Janus kinase (JAK) inhibitor tofacitinib led to a marked suppression of the IFN signature.ConclusionsA heterozygous gain-of-function mutation in STING can cause familial chilblain lupus. These findings expand the genetic spectrum of type I IFN-dependent disorders and suggest that JAK inhibition may be of therapeutic value.

Background Biomarkers for idiopathic inflammatory myopathies are difficult to identify and may involve expensive laboratory tests. We assess the potential for artificial intelligence (AI) to differentiate children with juvenile dermatomyositis (JDM) from healthy controls using nailfold capillaroscopy (NFC) images. We also assessed the potential of NFC images to reflect the range of disease activity with JDM. Methods A total of 1,120 NFC images from 111 children with active JDM, diagnosed between 1990 and 2020, and 321 NFC images from 31 healthy controls were retrieved from the CureJM JDM Registry. We built a lightweight and explainable deep neural network model called NFC-Net. Images were downscaled by interpolation techniques to reduce the computational cost. Results NFC-Net achieved high performance in differentiating patients with JDM from controls, with an area under the ROC curve (AUROC) of 0.93 (0.84, 0.99) and accuracy of 0.91 (0.82, 0.92). With sensitivity (0.85) and specificity (0.90) resulted in model precision of 0.95. The AUROC and accuracy for predicting clinical disease activity from inactivity were 0.75 (0.61, 0.81) and 0.74 (0.65, 0.79). Conclusion The good performance of the NFC-Net demonstrates that NFC images are sufficient for detecting often unrecognized JDM disease activity, providing a reliable indicator of disease status. Impact Proposed NFC-Net can accurately predict children with JDM from healthy controls using nailfold capillaroscopy (NFC) images. Additionally, it predicts the scores to JDM disease activity versus no activity. Equipped with gradients, NFC-Net is explainable and gives visual information beside the reported accuracies. NFC-Net is computationally efficient since it is applied to substantially downscaled NFC images. Furthermore, the model can be wrapped within an edge-based device like a mobile application that is accessible to both clinicians and patients.