Follow-Up of Renal Function in Patients With Fibromuscular Dysplasia

Objective: Fibromuscular dysplasia (FMD) often involves the renal arteries but longitudinal data on renal function in FMD remain scarce. Design and method: We retrospectively analyzed 249 patients with FMD seen at Maastricht University Medical Center between 2016 and 2024. For 133 patients, follow-up data on renal function were available with a median follow-up duration of 25 (interquartile range: 13-45) months. Data on estimated glomerular filtration rate (eGFR), blood pressure, and, when available, microalbuminuria were collected. Longitudinal changes in eGFR were analyzed using linear mixed models, complemented by paired tests between baseline and last measurement. Subgroup analyses evaluated the influence of age, hypertension, and vascular phenotype. Results: Linear mixed modeling demonstrated a significant decline in eGFR (0.57 ml/min/1.73 m2 per year, 95% CI: 0.23 to 0.92; p=0.001). Sensitivity analysis with a random slope model confirmed the decline (1.24 per year, 95% CI: 0.54 to 1.95; p<0.001). Paired analysis showed a mean decrease of 5.3 ml/min/1.73 m2 over 3.2 years (p<0.001). Patients without hypertension experienced a steeper decline than hypertensive patients (2.11 vs. 0.45 ml/min/1.73 m2 per year, interaction p=0.03). Age 60 years and older was associated with a faster decline, although the difference was not statistically significant. No differences were observed across FMD phenotypes or renal versus non-renal involvement. In cross-sectional analysis, the rate of decline of eGFR with age did not differ from that derived from population data. Nevertheless, the intercept of the regression line was slightly lower for the FMD patients but still in the normal range. No changes in micro-albuminuria were observed. Conclusions: In this large cohort, renal function, although normal, appeared to be slightly lower than in the population at large. The age-related decline in eGFR in FMS patients did not differ from that in a control population. Decline was more pronounced in non-hypertensive individuals, highlighting the importance of long-term follow-up irrespective of blood pressure status. These findings suggest that, contrary to the traditionally held view of FMD, subtle deterioration in renal function can occur and warrants careful monitoring.