Utility of Abdominal Fat Pad Aspiration in the Early Diagnosis of Systemic Amyloidosis: A Cross-sectional Study

Abstract

Introduction: Abdominal Subcutaneous Fat Pad aspiration (AFPA) is a quick, sensitive, and specific screening and diagnostic method for detecting amyloid deposits. This procedure can be performed in an outpatient setting. The present study aimed to demonstrate amyloid deposits in subcutaneous fat pad aspirates on Congo Red stained slides using polarised microscopy. Aim: To evaluate the diagnostic accuracy of abdominal fat pad aspiration cytology as a screening procedure for systemic amyloidosis. Materials and Methods: A cross-sectional study was conducted over a three-year period (January 2019 to July 2021) at SDM College of Medical Sciences and Hospital, Sattur, Dharwad. Fat pad aspirate slides stained with Congo Red stain were independently reviewed by two cytopathologists. Slides were examined under a polarising microscope and interpreted as either positive or negative for amyloid deposits based on the presence or absence of apple green birefringence. The data were evaluated using Microsoft Excel and Statistical Package for the Social Sciences (SPSS) software version 20.0. Results: The present study included 54 abdominal fat pad aspirates. The ages ranged between 29 and 80 years, with a mean age of presentation of 59 years. Among all AFPA samples, 35 (64.8%) were positive for amyloid, 16 (29.6%) were negative, and three (5.5%) were inconclusive for interpretation. Follow-up deep/visceral biopsies, such as kidney and bone marrow biopsies, were performed in 31 (57.4%) cases, and approximately half of these cases showed amyloid deposition on deep biopsy. AFPA demonstrated a sensitivity, specificity, positive predictive value, and diagnostic accuracy of 94%, 92%, 94%, and 93.3%, respectively, considering visceral biopsies including bone marrow and/or kidney as the gold standard. Conclusion: Abdominal fat pad aspiration is a quick, minimally invasive, outpatient-based procedure that helps in the early diagnosis of systemic amyloidosis before patients clinically present with complications.

Keywords

• congo red stain
• polarising microscopy
• systemic amyloidosis