Diagnosis of Primary Cutaneous Amyloidosis by Rapid 4,6-Diamidino-2-Phenylindole Staining

Background: Quick and accurate diagnosis of primary cutaneous amyloidosis (PCA) may be difficult because its symptoms are often subtle and nonspecific. Objective: We sought to review the literature on the roles of various staining methods in the diagnosis of amyloidosis and demonstrate added benefits of using rapid 4,6-diamidino-2-phenylindole (DAPI) staining in the diagnosis of PCA. Methods: Three groups of cases, namely, PCA, neurodermatitis, and prurigo nodularis, were retrieved from a computerized pathology database for study, and their paraffin-embedded tissue blocks were cut following standard procedures. The tissue sections were stained with three stains: hematoxylin-eosin (HE), Congo red, and DAPI stains, and examined under the microscope to compare the staining patterns of these three methods. We also performed amyloid keratin and apolipoprotein E (APOE) staining on the sections of PCA in order to further support our conclusion. The PCA sections were read by junior and senior dermatopathologists for comparison. Results: The sensitivity of DAPI staining for PCA was significantly higher than that of Congo red staining and HE staining (p < 0.001). This statement holds true whether the experiment was grouped in one sample or was divided into groups of junior and senior dermatopathologists (p < 0.001). The DAPI-positive staining areas, except for the nuclei, were consistent with the amyloid deposition areas. In this study, DAPI staining had a sensitivity of 98.6% and a specificity of 100%. Conclusion: DAPI staining could serve as a useful technique to establish the diagnosis of PCA, and its high efficacy in diagnosing PCA makes it less dependent on the experience levels of the evaluators. Additionally, the binding of DAPI to the A-T-rich sequence of double-stranded DNA suggests that amyloid may contain DNA or a similarly structured nucleic acid.