Comparative Analysis of Clinicopathological Features and Outcomes Between Kidney-Limited and Systemic Thrombotic Microangiopathy: A Study Based on a Semiquantitative Pathological Scoring System.

Objective: To systematically compare the clinicopathological features and prognostic outcomes of renal-limited thrombotic microangiopathy (RL-TMA) and systemic thrombotic microangiopathy (Sys-TMA) using a semiquantitative pathological scoring system. Methods: We retrospectively analyzed 47 patients with biopsy-proven TMA between 2018 and 2025, categorized as RL-TMA (n = 42) or Sys-TMA (n = 5) based on systemic manifestations. Clinical, pathological, and follow-up data were collected. A composite renal endpoint served as the primary outcome. Kaplan-Meier and Cox regression analyses were used for survival analysis and prognostic factor identification. Results: RL-TMA patients were older, with higher hemoglobin and platelet levels, lower lactate dehydrogenase, less complement C3 consumption, and significantly fewer multiorgan dysfunctions than Sys-TMA patients. Pathologically, Sys-TMA was dominated by acute microvascular lesions, whereas RL-TMA showed more chronic changes (glomerulosclerosis, arteriolar hyalinosis) and more frequent immune complex deposition. Total immunofluorescence intensity and IgG, IgG2, IgG4, and C1q deposition were significantly higher in RL-TMA (all P < 0.05). Over a median follow-up of 16-20 months, end-stage kidney disease incidence did not differ significantly between groups (9.5% vs 0%, P > 0.05). In RL-TMA, univariate analysis showed that lower hemoglobin was associated with worse renal outcomes (HR = 0.946, P = 0.004). Serum albumin showed no clear association (HR = 0.992, P = 0.862), while pathological scores lacked independent predictive value. Kaplan-Meier analysis showed no statistically significant difference in renal progression-free survival between the two groups (P = 0.97). Conclusion: This study delineates significant differences between RL-TMA and Sys-TMA across clinical, pathological, and prognostic dimensions, suggesting that RL-TMA may represent a distinct clinicopathological entity, warranting further validation in larger prospective studies. Given the small sample size of the Sys-TMA group, these results should be interpreted as exploratory and hypothesis-generating. Hemoglobin levels showed an association with renal outcomes in univariate analysis, but this finding requires further investigation in larger cohorts before any clinical utility can be established.