CD3 immunohistochemical staining in diagnosis of lymphocytic colitis

Number of intraepithelial lymphocytes and presence of a subepithelial band in normal colonic mucosa differs according to stainings and evaluation method

Chronic watery diarrhea is a frequent symptom. In approximately 10% of the patients, a diagnosis of microscopic colitis (MC) is established. The diagnosis relies on specific, but sometimes subtle, histopathological findings. As the histology of normal intestinal mucosa vary, discriminating subtle features of MC from normal tissue can be challenging and therefore auxiliary stainings are increasingly used. The aim of this study was to determine the variance in number of intraepithelial lymphocytes (IELs) and presence of a subepithelial band in normal ileum and colonic mucosa, according to different stains and digital assessment. Sixty-one patients without diarrhea referred to screening colonoscopy due to a positive feacal blood test and presenting with endoscopically normal mucosa were included. Basic histological features, number of IELs, and thickness of a subepithelial band was manually evaluated and a deep learning-based algorithm was developed to digitally determine the number of IELs in each of the two compartments; surface epithelium and cryptal epithelium, and the density of lymphocytes in the lamina propria compartment. The number of IELs was significantly higher on CD3-stained slides compared with slides stained with Hematoxylin-and-Eosin (HE) (p<0.001), and even higher numbers were reached using digital analysis. No significant difference between right and left colon in IELs or density of CD3-positive lymphocytes in lamina propria was found. No subepithelial band was present in HE-stained slides while a thin band was visualized on special stains. Conclusively, in this cohort of prospectively collected ileum and colonic biopsies from asymptomatic patients, the range of IELs and detection of a subepithelial collagenous band varied depending on the stain and method used for assessment. As assessment of biopsies from patients with diarrhea constitute a considerable workload in the pathology departments digital image analysis is highly desired. Knowledge provided by the present study highlight important differences that should be considered before introducing this method in the clinic.

Marginal zone lymphoma of extranodal sites: A review with an emphasis on diagnostic pitfalls and differential diagnosis with reactive conditions

Marginal zone lymphoma of the mucosa-associated lymphoid tissue (MALT lymphoma) represents 8% of all B-cell lymphomas and it is the most common small B-cell lymphoma arising at extranodal sites. The gold-standard test to establish a diagnosis of MALT lymphoma remains histopathologic analysis with the aid of immunohistochemistry (IHC) and/or flow cytometry immunophenotypic analysis. MALT lymphoma represents a progression from a persistent chronic inflammatory process, and therefore distinguishing MALT lymphoma from chronic inflammation by histopathology may be challenging in some cases. Despite recent trends to consider IGH rearrangement/clonality as a confirmatory diagnostic test of MALT lymphoma, this method is far from ideal for this purpose since a positive or a negative result does not necessarily confirm or exclude that a process is lymphoma or reactive. This test must be correlated with the morphologic findings. Moreover, MALT lymphoma may arise in association with underlying autoimmune conditions where clonal lymphoid populations are not uncommonly detected. Therefore, we believe that an integrated approach including detailed morphologic review in combination with IHC and/or flow cytometry is best to establish a diagnosis of MALT lymphoma in most cases. We present helpful morphologic tips to avoid potential diagnostic pitfalls at some of the most common extranodal sites, including the stomach, ocular adnexa/conjunctiva, salivary gland, lung, thymus, breast, thyroid, small and large intestine and the dura. The differential diagnosis of MALT lymphoma with IgG4-related disease is also discussed.

Microscopic Colitis Is Associated With a Reduced Risk of Colorectal Adenoma and Cancer: A Meta-Analysis

BACKGROUND

The study sought to conduct a systematic review and meta-analysis of the risk of colorectal adenoma or cancer in patients with microscopic colitis (MC).

METHODS

A comprehensive literature search of PubMed and EMBASE databases was performed. Pooled relative risks (RRs) and 95% confidence intervals (CIs) were calculated to examine the effect of MC on the risk of colorectal adenoma or cancer.

RESULTS

Twelve studies reporting the outcomes of 50 795 patients with MC were eligible for this meta-analysis. MC was negatively associated with the risk of colorectal adenoma compared with participants without MC (RR, 0.44; 95% CI, 0.33-0.58; P < .001; I2 = 87.3%). Also, the rate of colorectal cancer was lower in the patients with MC compared with the general population (RR, 0.62; 95% CI, 0.43-0.89; P = .01; I2 = 91.6%). In addition, sensitivity and subgroup analyses indicated that the results were robust.

CONCLUSIONS

The present systematic review indicated that patients with MC may be associated with a lower risk of colorectal adenoma or cancer. The clinical data support the current professional society guideline. A surveillance colonoscopy program is not recommended as standard for patients with MC.

Budesonide as induction therapy for incomplete microscopic colitis: A randomised, placebo-controlled multicentre trial

BACKGROUND AND AIMS

Incomplete microscopic colitis (MCi) is a subtype of microscopic colitis (MC). Budesonide is recommended as a first-line treatment for MC. However, randomised trials on efficacy of treatment in MCi are missing. We therefore performed a randomised, placebo-controlled trial to evaluate budesonide as induction therapy for MCi.

METHODS

Patients with active MCi were randomly assigned to either budesonide 9 mg once daily or placebo for 8 weeks in a double-blind, double-dummy design. The primary endpoint was clinical remission, defined as a mean of <3 stools/day and a mean of <1 watery stool/day in the 7 days before week 8.

RESULTS

Due to insufficient patient recruitment, the trial was discontinued prematurely. The intention-to-treat analysis included 44 patients (21 budesonide and 23 placebo). The primary endpoint of clinical remission at week 8 was obtained by 71.4% on budesonide and 43.5% on placebo (p = 0.0582). All clinical secondary endpoints were in favour of budesonide. Budesonide decreased the number of soft or watery stools (16.3 vs. 7.7, p = 0.0186) and improved health-related quality of life for all four dimensions of the short health scale. Adverse events with a suspected relation to study drug were reported in one patient in the budesonide group and two patients in the placebo group. Neither serious nor severe adverse events occurred during the double-blind phase.

CONCLUSIONS

Budesonide decreased the frequency of soft or watery stools and improved the patients' quality of life significantly in MCi, but the primary endpoint was not met due to the low sample size (type 2 error). Budesonide was safe and well tolerated during the 8-weeks treatment course.

European guidelines on microscopic colitis: United European Gastroenterology and European Microscopic Colitis Group statements and recommendations

INTRODUCTION

Microscopic colitis is a chronic inflammatory bowel disease characterised by normal or almost normal endoscopic appearance of the colon, chronic watery, nonbloody diarrhoea and distinct histological abnormalities, which identify three histological subtypes, the collagenous colitis, the lymphocytic colitis and the incomplete microscopic colitis. With ongoing uncertainties and new developments in the clinical management of microscopic colitis, there is a need for evidence-based guidelines to improve the medical care of patients suffering from this disorder.

METHODS

Guidelines were developed by members from the European Microscopic Colitis Group and United European Gastroenterology in accordance with the Appraisal of Guidelines for Research and Evaluation II instrument. Following a systematic literature review, the Grading of Recommendations Assessment, Development and Evaluation methodology was used to assess the certainty of the evidence. Statements and recommendations were developed by working groups consisting of gastroenterologists, pathologists and basic scientists, and voted upon using the Delphi method.

RESULTS

These guidelines provide information on epidemiology and risk factors of microscopic colitis, as well as evidence-based statements and recommendations on diagnostic criteria and treatment options, including oral budesonide, bile acid binders, immunomodulators and biologics. Recommendations on the clinical management of microscopic colitis are provided based on evidence, expert opinion and best clinical practice.

CONCLUSION

These guidelines may support clinicians worldwide to improve the clinical management of patients with microscopic colitis.

5-Hydroxy-4-methoxycanthin-6-one alleviates dextran sodium sulfate-induced colitis in rats via regulation of metabolic profiling and suppression of NF-κB/p65 signaling pathway

BACKGROUND

5-Hydroxy-4-methoxycanthin-6-one (PQ-A) is the main active compound in Ramulus et Folium Picrasmae, a Chinese herbal medicine commonly used in colitis treatment.

PURPOSE

To clarify PQ-A's role and mechanism in colitis treatment based on a non-targeted metabolomics study.

METHODS

Rats with ulcerative colitis (UC) established with 4% dextran sulfate sodium (DSS) were orally treated with PQ-A. Body weight, disease activity index (DAI), colon length, biochemical parameters (MDA and SOD), and histopathological score in colon tissue were measured. A UPLC-Q-TOF-MS/MS approach-based metabolomics analysis was conducted to explore the underlying mechanisms of PQ-A in colitis treatment. Inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-10) concentrations in serum and their protein levels in the colon were determined. CD3 and NF-κB/p65 immunohistochemistry in the colon was semi-quantified. The related protein or mRNA in IKK-NF-κB/p65 signaling pathway was measured by Western blotting or RT-PCR, respectively. Potential molecular interactions between PQ-A and NF-κB/p65 was predicted using DS 2.5 software.

RESULTS

PQ-A significantly prevented body weight loss and colonic shortening in colitic rats, and reduced the DAI and histopathologic score as well. PQ-A decreased MDA levels in the UC rat serum and increased those of SOD. Metabolomics results revealed forty-nine differential metabolites as biomarkers of DSS-induced colitis, demonstrating that the path-mechanism of colitis involved the perturbation of eight metabolic pathways, including alpha-linolenic acid and linoleic acid metabolism, sphingolipid metabolism, retinol metabolism, bile acid metabolism, et al. Thirty-six biomarkers were especially reversed to normal-like levels by PQ-A via regulation of alpha-linolenic acid and linoleic acid metabolism, sphingolipid metabolism, and retinol metabolism, which effectively hinted the potential pharmacological mechanism of PQ-A related to NF-κB/p65 inflammatory signaling. Molecular docking results predicted high affinity interaction between PQ-A and NF-κB/p65, involving hydrogen-bond interactions at five amino acid residues, suggesting NF-κB/p65 as a target. PQ-A decreased TNF-α, IL-1β, and IL-6 concentrations in serum and their protein levels in colon tissue in colitic rats. CD3, MYD88, p-IκBα, NF-κB/p65, and p-NF-κB/p65 expression levels decreased, whereas those of IKKβ and IκBα increased in colitic tissue following PQ-A treatment. PQ-A strongly inhibited nuclear translocation of NF-κB/p65.

CONCLUSIONS

We provide an overview of PQ-A's possible mechanism of action in colitis treatment based on serum non-targeted metabolomics. PQ-A treatment can protect rats against DSS-induced colitis by suppressing the NF-κB/p65 signaling pathway.

Serotonin in the Pathogenesis of Lymphocytic Colitis

Lymphocytic colitis (LC) is a chronic inflammatory disease associated with watery diarrhea, abdominal pain, and colonic intraepithelial lymphocytosis. Serotonin (5-hydroxytryptamine, 5-HT) is reported to increase in certain colon diseases; however, little is known regarding its metabolism in LC. In the present work, the level of 5-HT in serum and the number of enteroendocrine cells (EECs) as well as the expression of the 5-HT rate-limiting enzyme tryptophan hydroxylase 1 (TPH1) in colonic biopsies and urine 5-hydroxyindoeoacetic acid (5-HIAA) were determined in 36 LC patients that were treated with budesonide and 32 healthy controls. The 5-HT serum and 5-HIAA urine levels were measured using ELISA, the EEC number was determined immunohistochemically, and the colonic TPH1 mRNA expression was determined using RT-PCR. The levels of 5-HT and 5-HIAA and the number of EECs were higher in LC patients than in the controls, and positive correlations were observed between the 5-HT and 5-HIAA levels, 5-HT and EEC number, TPH1 mRNA and EEC number, as well as the severity of disease symptoms and 5-HIAA. Budesonide decreased the levels of 5-HT, 5-HIAA, and TPH1 expression and the number of EECs to values that did not differ from those for controls. In conclusion, the serotonin metabolism may be important for LC pathogenesis, and the urinary level of 5-HIAA may be considered as a non-invasive marker of this disease activity.

Non-neoplastic colorectal disease biopsies: evaluation and differential diagnosis

A wide variety of non-neoplastic conditions may be encountered on colorectal biopsy encompassing idiopathic, infectious, vascular and immune-mediated aetiologies. Although interpretation of such biopsies may be challenging, appreciation of the dominant pattern of injury and subsequent host response may allow for a more focused histological diagnosis in the correct clinical and endoscopic setting. This article aims to provide a systematic, methodical approach to the assessment of such biopsies, concentrating mainly on diagnoses other than inflammatory bowel disease.

Microscopic colitis: pathophysiology and clinical management

Microscopic colitis is a chronic inflammatory disease of the colon that frequently causes chronic watery diarrhoea that might be accompanied by abdominal pain, nocturnal diarrhoea, urgency, and faecal incontinence. These symptoms lead to poor quality of life and increased health-care costs. Diagnosis relies on histological examination of multiple biopsy samples from the colonic mucosa, which often show no or only few abnormalities on endoscopy. Two major histological subtypes can be distinguished-collagenous colitis and lymphocytic colitis-but incomplete and variant forms with fewer characteristic features have been reported. Here we summarise the latest evidence on epidemiology, pathogenesis, and risk factors, and discuss established and novel therapeutic options for clinical remission. Finally, we propose an updated treatment algorithm. Further prospective studies are needed to clarify the natural history of microscopic colitis, supported by validated criteria for the assessment of disease activity.

An investigation of European pathologists' approach to diagnose microscopic colitis

Microscopic colitis (MC) comprising lymphocytic colitis (LC), collagenous colitis (CC) and the incomplete forms of microscopic colitis (MCi) are frequent causes of chronic watery diarrhea. The diagnosis is based on specific histological features in colonic biopsies. Especially regarding MCi, the histological features may be subtle. The PRO-MC collaboration was established in 2016 with the aims to systematically describe the disease course and to validate the diagnostic criteria of MC. In the present study, we analysed pathologists' initial approach to diagnose MC. Five pathologists with expertise in gastro-intestinal pathology reviewed the first 10 cases enrolled in the PRO-MC registry in six of the participating centres. Despite considerable differences in strategies in biopsy sampling, in choice of stains and in minimum number of biopsies and segments required for diagnosing MC, inter-observer agreement between the participating centres and expert pathologists as well as among the latter was substantial. Disagreed cases most often related to difficulties in distinguishing between MC subgroups. We recommend that pathologists as well as clinicians reach consensus in their diagnostic approach to MC, which is a prerequisite to compare MC cohorts internationally and to facilitate clinical MC trials and follow-up studies.

Nucleus and cytoplasm-based segmentation and actor-critic neural network for acute lymphocytic leukaemia detection in single cell blood smear images

Acute lymphoblastic leukaemia (ALL), which is due to the malfunctioning in the bone marrow, is common among people all over the world. The haematologist suffers a lot to discriminate the presence of leukaemia in the patients using the blood smears. To overcome the inaccuracy and reliability issues, this paper proposes an automatic method of leukaemia detection, named chronological Sine Cosine Algorithm-based actor-critic neural network (Chrono-SCA-ACNN). Initially, the blood smear images are segmented using the proposed entropy-based hybrid model, from which the image-level features and statistical features are extracted from the segments. Then, the selected features are applied to the proposed classifier, which detects the leukaemia. In the proposed Chrono-SCA-ACNN, the optimal weights are selected by the proposed Chrono-SCA, which is the integration of the chronological concept in the SCA. Finally, the experimentation is performed using the ALL-IDB2 database, and the effectiveness of the proposed method over the existing methods is evaluated. From the analysis, the accuracy of the proposed method is found to be 0.99, which proves that it outperforms the existing classification methodologies. Graphical abstract Block diagram of proposed Leukaemia detection. The main aim of the paper is to segment and classify the WBCs for ALL detection in single cell blood smear images. Initially, the blood smear image is subjected to pre-processing in order to enhance the quality of the input image so as to make it effective for the further processes associated with Leukaemia detection. The pre-processed image is applied to the segmentation process that segments the cytoplasm and nucleus using the Entropy-based hybrid model. The entropy-based hybrid model is developed using the FCM and active contour to segment the cytoplasm and nucleus that is fused using the entropy. The segments are subjected to the feature extraction that extracts the statistical features and the color histogram-based features from the segments. The features are presented to the Actor-Critic Neural Network and the weights of the Neural Network (NN) are optimally tuned using the proposed Chrono-SCA. The block diagram of the proposed method of leukaemia detection is depicted in Fig. 1.

Mutual Information based hybrid model and deep learning for Acute Lymphocytic Leukemia detection in single cell blood smear images

BACKGROUND AND OBJECTIVE

Due to the development in digital microscopic imaging, image processing and classification has become an interesting area for diagnostic research. Various techniques are available in the literature for the detection of Acute Lymphocytic Leukemia from the single cell blood smear images. The purpose of this work is to develop an effective method for leukemia detection.

METHODS

This work has developed deep learning based leukemia detection module from the blood smear images. Here, the detection scheme carries out pre-processing, segmentation, feature extraction and classification. The segmentation is done by the proposed Mutual Information (MI) based hybrid model, which combines the segmentation results of the active contour model and fuzzy C means algorithm. Then, from the segmented images, the statistical and the Local Directional Pattern (LDP) features are extracted and provided to the proposed Chronological Sine Cosine Algorithm (SCA) based Deep CNN classifier for the classification.

RESULTS

For the experimentation, the blood smear images are considered from the AA-IDB2 database and evaluated based on metrics, such as True Positive Rate (TPR), True Negative Rate (TNR), and accuracy. Simulation results reveal that the proposed Chronological SCA based Deep CNN classifier has the accuracy of 98.7%.

CONCLUSIONS

The performance of the proposed Chronological SCA-based Deep CNN classifier is compared with the state-of-the-art methods. The analysis shows that the proposed classifier has comparatively improved performance and determines the leukemia from the blood smear images.

Microscopic colitis: a population-based case series over a 9-year period in Northern Ireland

AIM

We report clinicopathological experience of microscopic colitis (MC) in a population-based case series in Northern Ireland over a 9-year period.

METHOD

The pathology laboratory information system within a large teaching centre serving two healthcare trusts was interrogated for cases coded between 2008 and 2016 as collagenous colitis (CC) or lymphocytic colitis (LC). Demographic, clinical and follow-up information was collected from healthcare records.

RESULTS

A total of 326 new diagnoses of MC were identified, an average annual incidence of 6.7 per 100 000 population. The average annual incidence of CC and LC was 5.0 and 1.7 per 100 000 population, respectively. For coding reasons it is likely that LC data are incomplete. Of 191 cases diagnosed by specialist gastrointestinal pathologists, 141 patients had CC and 50 patients had LC. Both CC and LC predominantly involved women aged 60-79. Some 15% demonstrated endoscopic abnormalities. Endoscopic sampling protocols varied widely: 30% of individuals with CC and 32% of those with LC had the right and left colon sampled separately, with histology concordant in 95% of cases. Of the 191 cases, only one case (of LC) was refractory to treatment; the rest exhibited a clinical response. Only 35 patients had follow-up endoscopy and biopsies, and three of each diagnosis showed persistent disease on histology.

CONCLUSION

Overall, CC and LC are benign conditions with similar demographics, clinical associations, management and outcomes. Separate sampling of the right and left colon is advised at colonoscopy if this diagnosis is being considered, but left colonic sampling, which can be performed at flexible sigmoidoscopy, will diagnose the vast majority of cases.

The subtypes of microscopic colitis from a pathologist's perspective: past, present and future

Microscopic colitis (MC) is a chronic inflammatory bowel disease, encompassing a triad of chronic diarrhea, normal endoscopy and characteristic histological findings. MC embraces two histological subtypes described as lymphocytic colitis (LC) and collagenous colitis (CC). The diagnostic criteria of MC were established several years ago and the histological description of LC and CC was based almost exclusively on heamatoxylin-eosin (HE) stained sections. Since the establishment of the diagnostic criteria, important changes have occurred in the concept and diagnostic methods of MC: the emergence of the entity "microscopic colitis incomplete" (MCi), comprising collagenous colitis incomplete (CCi) and lymphocytic colitis incomplete (LCi) and pathologists' increasing use of special stains in everyday diagnostics. The diagnostic challenges of today are threefold: which stains to apply to properly distinguish between MC, MCi and slight inflammatory changes, how to handle cases of diagnostic uncertainty and how to minimize inter observer variability. The views of this article are from the pathologist's perspective. We describe the changes in criteria and diagnostic methods of MC occurring over time, discus pathologists' diagnostic challenges and suggest how these can be met: by automated image analysis of tissue sections and by international collaboration under auspices of the PRO-MC collaboration, a European collaboration on the disease course of MC.

A segmentation method based on HMRF for the aided diagnosis of acute myeloid leukemia

BACKGROUND AND OBJECTIVES

The diagnosis of acute myeloid leukemia (AML) is purely dependent on counting the percentages of blasts (>20%) in the peripheral blood or bone marrow. Manual microscopic examination of peripheral blood or bone marrow aspirate smears is time consuming and less accurate. The first and very important step in blast recognition is the segmentation of the cells from the background for further cell feature extraction and cell classification. In this paper, we aimed to utilize computer technologies in image analysis and artificial intelligence to develop an automatic program for blast recognition and counting in the aspirate smears.

METHODS

We proposed a method to analyze the aspirate smear images, which first performs segmentation of the cells by k-means cluster, then builds cell image representing model by HMRF (Hidden-Markov Random Field), estimates model parameters through probability of EM (expectation maximization), carries out convergence iteration until optimal value, and finally achieves second stage refined segmentation. Furthermore, the segmentation results are compared with several other methods using six classes of cells respectively.

RESULTS

The proposed method was applied to six groups of cells from 61 bone marrow aspirate images, and compared with other algorithms for its performance on the analysis of the whole images, the segmentation of nucleus, and the efficiency of calculation. It showed improved segmentation results in both the cropped images and the whole images, which provide the base for down-stream cell feature extraction and identification.

CONCLUSIONS

Segmentation of the aspirate smear images using the proposed method helps the analyst in differentiating six groups of cells and in the determination of blasts counting, which will be of great significance for the diagnosis of acute myeloid leukemia.

CD3+ lymphocytosis in the peri-implant membrane of 222 loosened joint endoprostheses depends on the tribological pairing

Background and purpose - The most frequent cause of arthroplasty failure is aseptic loosening-often induced by particles. Abrasion material triggers inflammatory reactions with lymphocytic infiltration and the formation of synovial-like interface membranes (SLIM) in the bone-implant interface. We analyzed CD3 quantities in SLIM depending on articulating materials and possible influences of proven material allergies on CD3 quantities. Patients and methods - 222 SLIM probes were obtained from revision surgeries of loosened hip and knee arthroplasties. SLIM cases were categorized according to the SLIM-consensus classification and to the particle algorithm. The CD3 quantities were analyzed immunohistochemically, quantified, and correlated to the particle types. Results - Metal-metal pairings showed the highest CD3 quantities (mean 1,367 counted cells). CD3 quantities of metal-polyethylene (mean 243), ceramic-polyethylene (mean 182), and ceramic-ceramic pairings (mean 124) were significantly smaller. Patients with contact allergy to implant materials had high but not statistically significantly higher CD3 quantities than patients without allergies. For objective assessment of the CD3 response as result of a pronounced inflammatory reaction with high lymphocytosis (adverse reaction), a defined CD3 quantity per high power field was established, the "CD3 focus score" (447 cells/0.3 mm², sensitivity 0.92; specificity 0.90; positive predictive value 0.71; negative predictive value 0.98). Interpretation - The high CD3 quantities for metal-metal pairings may be interpreted as substrate for previously described adverse reactions that cause severe peri-implant tissue destruction and SLIM formation. It remains unclear whether the low CD3 quantities with only slight differences in the various non-metal-metal pairings and documented contact allergies to implant materials have a direct pathogenetic relevance.

Towards a new paradigm of microscopic colitis: Incomplete and variant forms

Microscopic colitis (MC) is a chronic inflammatory bowel disease that has emerged in the last three decades as a leading cause of chronic watery diarrhoea. MC classically includes two main subtypes: lymphocytic colitis (LC) and collagenous colitis (CC). Other types of histopathological changes in the colonic mucosa have been described in patients with chronic diarrhoea, without fulfilling the conventional histopathological criteria for MC diagnosis. Whereas those unclassified alterations remained orphan for a long time, the use of the term incomplete MC (MCi) is nowadays universally accepted. However, it is still unresolved whether CC, LC and MCi should be considered as one clinical entity or if they represent three related conditions. In contrast to classical MC, the real epidemiological impact of MCi remains unknown, because only few epidemiological studies and case reports have been described. MCi presents clinical characteristics indistinguishable from complete MC with a good response to budesonide and cholestiramine. Although a number of medical treatments have been assayed in MC patients, currently, there is no causal treatment approach for MC and MCi, and only empirical strategies have been performed. Further studies are needed in order to identify their etiopathogenic mechanisms, and to better classify and treat MC.