医网情深：AMG病理实习的家庭作业之一——在美国行医系列 (刀评：Erina是美国医学毕业生，申请外科住院医生未果，经过反复思考和征求朋友的意见，决定今年转向申请病理住院医生，但疫情期间苦于寻找不到病理实习甚至见习的机会和单位。经西海岸的美国临床轮转公司（AMC）的推荐，来到纽约，与一位先期抵达的CMG同学一起接受我的四周强化培训。第一周开始学习实验室技术，冰冻病理授课，胃肠病理阅片和学习两种不同公司的软件sign out 病例。学习兴致盎然，急着学习写病例小结，mini综述。今天交了第一篇作业：与我在诊所阅片中碰巧遇到的有趣对比病例淋巴细胞性和胶原性结肠炎的对比、诊断和鉴别诊断。） Case study note: Microscopic colitis—diagnosis and differential diagnosis Erina McKenny， MD （Note：the interesting cases were provided by Dr. He, while following his office lab sign-out. After reviewing literature and references, summary of this interesting GI clinical identity are as follows). Microscopic colitis is characterized by intermittent, chronic, watery diarrhea with acute onset. Associated symptoms include mild abdominal pain or weight loss. More severe weight loss indicates a differential diagnosis of celiac disease, which can be ruled out if symptoms resolve with a gluten-free diet. It is noteworthy to add, however, that there can be a concurrent diagnosis of microscopic colitis and celiac disease due to an autoimmune association. Patients with microscopic colitis often meet the symptomatic criteria for irritable bowel syndrome (improvement of abdominal discomfort with defecation, onset associated with change in stool frequency and/or onset associated with a change in appearance of stool). Older age, female gender, and a shorter duration of diarrhea predict a diagnosis of microscopic colitis rather than irritable bowel syndrome. There is an association between microscopic colitis and non-steroidal anti-inflammatory drugs, proton pump inhibitors, and selective serotonin reuptake inhibitors. Biopsy results show inflammatory infiltrate in the lamina propria with a predominance of plasma cells and lymphocytes, indicating chronicity. Diagnostic findings are intraepithelial lymphocytes in the surface epithelium and crypts. The two main subtypes of microscopic colitis are collagenous and lymphocytic. The main distinction between the two subtypes is the presence of a thickened subepithelial collagen band on histology.The key histological feature of lymphocytic colitis is an elevated number of surface intraepithelial lymphocytes, which are mostly cytotoxic CD8+ T cells. 15-20 intraepithelial lymphocytes per 100 epithelial cells indicate a diagnosis of lymphocytic colitis. Intraepithelial lymphocytes may be patchy and the subclassification is associated with less inflammation in the lamina propria (colonic lymphocytosis). Lymphocytes tend to be more prominent in the surface epithelium but may also be present in crypts. The diagnostic finding for collagenous colitis is a continuous subepithelial fibrous band underneath the surface epithelium that is greater than 10 micrometers. There is often an irregular, ragged interface between the lower aspect of the collagen deposits and superficial lamia propria. The surface epithelium tends to be sloughed. Paneth cell metaplasia is often present in the crypt bases. Crypt architecture is mostly retained, but there is occasional branching and dilation of crypts. A subgroup of patients exist that do not match the criteria for either lymphocytic or collagenous microscopic colitis. The terminology used for biopsies of these patients is microscopic colitis, not otherwise specified, or microscopic colitis, incomplete. Examples of such patients described are those who exhibit a mild increase in intraepithelial lymphocytes with a normal or slightly enhanced width of the collagen band. A 2011 retrospective review of a consecutive cohort of such patients concluded that microscopic colitis should be a single entity rather than divided into subclassifications of lymphocytic or collagenous. The conclusion was supported by the findings that despite inconsistencies in histologic features, the clinical symptoms of the patients were indistinguishable from patients who met the criteria for the lymphocytic or collagenous subtypes. Treatment for microscopic colitis often begins with loperamide, with a progression to bismuth or budesonide based on symptom severity. If patients are unresponsive, drug history and studies for celiac disease should be reevaluated. Patients treated with budesonide often require maintenance treatment and should be monitored for steroid-associated complications. References 1. Pardi, Darrell S. Microscopic Colitis: Diagnosis and Treatment. American College of Gastroenterology. Uploaded September 23rd, 2016. Accessed online via https://www.youtube.com/watch?v=6ytCXvidwFA&t=1103s 2. Cotter TG, Pardi DS. Editorial: additional evidence for drug-induced microscopic colitis. Alimentary Pharmacology & Therapeutics [Internet]. Alimentary Pharmacology & Therapeutics; 2016;43:1343–4. Available from: https://dx.doi.org/10.1111/apt.1362 3. Lamps, Laura W. Microscopic Colitis. ExpertPath. Accessed May 18th, 2021 via Elselvier. 4. Hempel KA, Sharma AV. Collagenous And Lymphocytic Colitis. [Updated 2020 Sep 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK541100/ 5. Guagnozzi D, Landolfi S, Vicario M. Towards a new paradigm of microscopic colitis: Incomplete and variant forms. World Journal of Gastroenterology [Internet]. World Journal of Gastroenterology; 2016;22:8459. Available from: https://dx.doi.org/10.3748/wjg.v22.i38.8459 6. Bjørnbak C, Engel PJ, Nielsen PL, Munck LK. Microscopic colitis: clinical findings, topography and persistence of histopathological subgroups. Aliment Pharmacol Ther. 2011 Nov;34(10):1225-34. doi: 10.1111/j.1365-2036.2011.04865.x. Epub 2011 Oct 3. PMID: 21967618. 5/19/2021 New York