Objective To explore the clinicopathological features of light chain amyloid casts (LCAC) and grasp a deeper understanding of LCAC.
Methods After reviewing the profiles of renal pathology at Guangzhou Kingmed Medical Laboratory Center from January 2018 to June 2021, LCAC patients were assigned into two groups of pure light chain amyloid casts (I-LCAC) and LCAC plus light chain amyloid nephropathy (LCAC&AL) group. All specimens were examined by light microscopy, immunofluorescence, electron microscopy and immunoelectron microscopy through semi-quantitative scoring.
Results A total of 131 patients were diagnosed with light chain cast nephropathy (LCCN) during the same period. Among which, 15 cases belonged to LCAC (11.5%), including I-LCAC group (n=10) and LCAC&AL group (n=5); 9 cases of LCAC were identified as multiple myeloma, including I-LCAC group (n=7) and LCAC&AL group (n=2) and the inter-group difference was not statistically significant; As compared with LCAC&AL group, I-LCAC group had higher serum creatinine levels (766.1±472.5)μmol/Lvs (82.8±22.5)μmol/L and incidence of anemia (100% vs 40%)(P<0.05); The mean number of starch casts per square millimeter in renal tissue of I-LCAC group was significantly more than that of LCAC&AL group (7.3±5.0)/mm²vs (0.3±0.1)/mm², P<0.05. The most common type of light chain was λ type. And the mean number of starch casts per square millimeter was correlated positively with serum creatinine level (R2=0.593).
Conclusion Multiple myeloma is the most common cause of LCAC. The casts are predominantly concentric and layered, central area is faintly stained while the edge of argyrophilic pathology appears "eyelash-like" with a positive Congo red stain. Polarized light microscope reveals yellow-green birefringence staining characteristics. Patients with I-LCAC pathological type are more susceptible to renal function injury than LCAC&AL group. The greater the mean number of starch tubes per square millimeter, the worse the renal function.
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