C4d, a new diagnostic modality for cutaneous amyloidosis: a comparison of C4d expression in cutaneous amyloidosis and cutaneous lichen planus

Amyloidosis is a rare disease characterized by the extracellular deposition of a misfolded protein in multiple organs. Cutaneous amyloidosis (CA) is diagnosed by detecting amyloid deposition in the skin. Lichen amyloidosis (LA) and macular amyloidosis (MA) without visceral involvement are two of its more prevalent types. This case-control study was conducted to evaluate C4d staining in amyloidosis to determine whether it could be used as a diagnostic tool for amyloidosis. Moreover, the results of C4d expression in amyloidosis with colloid bodies in lichen planus (LP) were compared. Therefore, 41 cases of CA and 43 cases of LP were selected. All samples were stained with C4d immunostain. 12 of 41 cases of CA had apple green birefringence; however, all of them were positive for C4d, the same as the LP group. The CA group had 100% C4d and 29% Congo red sensitivities (P < 0.05). C4d had 100% sensitivity for colloid bodies in LP. Therefore, the C4d stain could serve as a new IHC marker for highlighting the colloid bodies. C4d immunohistochemical (IHC) staining could be a very valuable ancillary tool for diagnosing amyloidosis, although it did not differentiate amyloid deposition from colloid bodies of LP.