C4d deposits and a new diagnostic modality for amyloidosis

Amyloidosis is characterized by the deposition of misfolded protein in various organs. The diagnosis of amyloidosis is based on the detection of amyloid deposits by Congo red stain under polarized microscopy. This study was done to investigate C4d deposition in amyloidosis and to determine whether C4d staining can be used as a new diagnostic tool for amyloidosis. This retrospective study included 32 patients who underwent biopsy at our medical center. The samples were stained by Congo red and C4d immunohistochemical stain, respectively. The biopsy samples from 18 patients who had been finally diagnosed with amyloidosis were included as the amyloidosis group, and 14 patients diagnosed with fibrosis were included as the control group. C4d was detected in 17 of 18 amyloidosis patients. On the other hand, in the control group, C4d deposit was not observed in any patient diagnosed with fibrosis. C4d immunohistochemical staining can be a highly useful modality for the diagnosis of amyloidosis. Furthermore, C4d can be applied as a tool for the differential diagnosis of amyloidosis and fibrosis.