Clinical relevance of serum lysozyme in sarcoidosis with kidney impairment

The clinical significance of serum lysozyme in sarcoidosis remains unclear. This study aimed to evaluate the clinical characteristics and kidney function of sarcoidosis patients with elevated serum lysozyme. We retrospectively analyzed 28 patients with sarcoidosis and measured levels of serum lysozyme. Clinical characteristics, laboratory data, and estimated glomerular filtration rate (eGFR) were evaluated. Median age was 57 years (interquartile range, 43-70 years), and 21% were men. High serum lysozyme levels were associated with a greater number of organ involvements (median 4 vs. 2, <i>p</i> = 0.022) and more frequent renal involvement (50 vs. 7%, <i>p</i> = 0.033). Serum lysozyme levels correlated inversely with eGFR (<i>r</i> = -0.814). Median serum lysozyme level was significantly higher in patients with renal sarcoidosis (RS) (30.2 μg/mL) than in non-RS patients (9.5 μg/mL, <i>p</i> = 0.003). Prominent intracytoplasmic lysozyme staining in proximal tubular epithelial cells was observed in the kidney of RS patients. Multiple regression analysis identified serum lysozyme as an independent risk factor for eGFR decline. Elevated serum lysozyme in sarcoidosis was associated with multiorgan involvements and renal impairment. Lysozyme may contribute to tubulointerstitial injury in RS, potentially through tubular reabsorption and cytotoxic effects. Further studies are warranted to clarify the role of lysozyme in the pathogenesis of RS.