Background & AimsDespite debilitating symptoms, no standardized disease severity index exists for microscopic colitis (MC). This gap hinders alignment with U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA) standards, which emphasize the importance of patient-reported outcome measures (PROMs) in new therapy approval. This study aimed to validate the Microscopic Colitis Symptom Questionnaire (MCSQ) and develop the Microscopic Colitis Score (MCS), a novel disease severity index.MethodThis prospective, multicenter study included 131 patients with biopsy-confirmed MC (67 remission, 64 active disease). Patients completed MCSQ and health-related quality of life (HRQoL) assessments [IBDQ-32, Short Health Scale (SHS)] at baseline and follow-up. Clustering analysis systematically identified distinct disease severity groups. MCS was developed as a composite score derived from MCSQ.ResultsFactor analysis revealed a three-factor MCSQ model with good internal consistency (Cronbach’s alpha = 0.88). Test–retest reliability (intraclass correlation coefficient = 0.88) and responsiveness to treatment (P < .01) of all MCSQ items were high. MCS, ranging from 0 (asymptomatic) to 15 (maximum symptoms), correlated strongly with HRQoL measures such as IBDQ-32 total score (rp=−0.78), IBDQ-32 bowel symptoms (rp=−0.80), and SHS bowel symptoms (rp=0.69). Receiver–operating characteristic curves indicated that MCS could accurately identify patients in remission [as per Hjortswang criteria; area under the curve (AUC) = 0.85], as well as mild (AUC = 0.97), moderate (AUC = 0.93), or severe disease (AUC = 0.96).ConclusionsMCSQ and MCS are valid, reliable, and responsive tools that meet FDA and EMA standards. Both accurately reflect the diverse symptoms of MC. Compared to the binary Hjortswang criteria, MCS provides a nuanced evaluation of disease activity and holds promise for assessing therapeutic efficacy in future trials.

Lymphocytic and collagenous colitis, uncommon entities that are identifiable by histopathologic examination only, and intestinal spirochetosis may cause chronic diarrhea. Data on incidence, histopathology, and diseases associated with these infrequent forms of colitis are reviewed. Etiology and pathogenesis of lymphocytic and collagenous colitis are still unknown, but immuno-inflammatory factors may be involved in both forms as well as, in collagenous colitis, primary disorders of collagen metabolism or drug-induced toxic effects. The significance of intestinal colonization by spirochetes is disputed; however, recent results indicate that these microorganisms are capable of inducing disease.

Based on pertinent data from the literature and on their personal experience, the authors present a clinicopathological review of collagenous colitis, microscopic (lymphocytic) colitis, and lymphoid follicular proctitis. The following aspects of these three newly recognized forms of colitis are emphasized: clinical features, light microscopy, histological diagnostic problems, immunological aspects, coexisting diseases, treatment, etiology, and pathogenesis. Special attention is paid to possible overlap between collagenous colitis and microscopic (lymphocytic) colitis.