Utility of abdominal skin punch biopsy for detecting systemic amyloidosis

Background Early and accurate diagnosis of systemic amyloidosis (SA) is critical for optimal patient outcomes. Biopsy of clinically uninvolved skin and subcutaneous tissue including abdominal skin punch biopsy (ASPB) is often used as a surrogate for affected organ sampling. There is a lack of published data on the sensitivity and specificity of ASPB for diagnosing SA. Methods Retrospective chart review between 2000 and 2020 of all ASPB was performed to diagnose SA. Amyloid deposition was confirmed by Congo red stain. Study group includes patients with histopathologically and clinically confirmed diagnosis of SA. Control group includes patients without histopathology of amyloid deposition and no clinical SA. Results Forty-one patients meeting inclusion criteria were analyzed; 23 study group and 18 control group patients. The overall diagnostic sensitivity of ASPB was 43% (95% CI 23%-66%) and the specificity 100% (95% CI 81%-100%). The AL amyloidosis diagnostic sensitivity was 64% (95% CI 35%-87%). ASPB >10 mm in depth had 100% (95% CI 54%-100%) sensitivity compared to 24% for depth <= 10 mm (P = .002). Conclusions ASPB is a minimally invasive and highly specific method of diagnosing SA. It is particularly sensitive for diagnosing AL amyloidosis and the diagnostic sensitivity can be significantly improved with adequate biopsy depth and diameter.