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Abdominal fat pad aspiration biopsy for tissue confirmation of systemic amyloidosis: specificity, positive predictive
1Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710, USA. guy00005@duke.edu
Abstract:
Abdominal fat pad fine-needle aspiration biopsy (FNAB) is considered the method of choice for confirmation of systemic amyloidosis. Due to our impression that positive results are rare in our FNA service, we retrospectively analyzed our results. Forty-five samples collected from 45 patients over 3 yr were reviewed. Of the 7 patients with positive Congo red-stained FNAB specimens, all 7 (100%) had documented amyloidosis. Of the 33 patients with negative Congo red fat samples, 28 (85%) were disease-free. Of the 5 patients with inadequate samples, 2 (40%) were later diagnosed with disease. We demonstrate excellent specificity (100%). The positive predictive value, documented in only a few previous studies, is likewise excellent (100%). Sensitivity is low (58%) and inadequacy is high (11%). Improvement in technique, such as concurrent cell block preparation, may help avoid inadequate specimens. Difficulties in confirming amyloidosis also include interpretation of the Congo red stain (pale-stained amyloid fibrils and collagen birefringence).
Insights
Abdominal fat pad fine-needle aspiration biopsy (FNAB) confirms systemic amyloidosis with 100% specificity. However, low sensitivity and high inadequacy rates highlight the need for improved FNAB techniques for accurate amyloidosis diagnosis.
Area of Science:
- Medical Diagnostics
- Pathology
- Nephrology
Background:
- Systemic amyloidosis diagnosis relies heavily on abdominal fat pad fine-needle aspiration biopsy (FNAB).
- Previous studies on FNAB for amyloidosis diagnosis are limited.
- Retrospective analysis of FNAB results was conducted due to perceived rarity of positive findings.
Purpose of the Study:
- To evaluate the diagnostic performance of abdominal fat pad FNAB for systemic amyloidosis.
- To assess the specificity, sensitivity, and predictive values of FNAB in a real-world clinical setting.
- To identify limitations and suggest improvements for FNAB procedures in amyloidosis diagnosis.
Main Methods:
- Retrospective review of 45 abdominal fat pad FNAB samples from 45 patients over three years.
- Analysis of Congo red staining results and correlation with documented amyloidosis diagnoses.
- Evaluation of specimen adequacy and diagnostic yield.
Main Results:
- Excellent specificity (100%) and positive predictive value (100%) were observed.
- Sensitivity was low at 58%, and specimen inadequacy was high at 11%.
- Of 33 negative Congo red samples, 85% were disease-free; 40% of inadequate samples were later diagnosed with amyloidosis.
Conclusions:
- Abdominal fat pad FNAB demonstrates high specificity and positive predictive value for systemic amyloidosis.
- Low sensitivity and high inadequacy rates necessitate technique improvements, such as concurrent cell block preparation.
- Interpretation challenges of Congo red staining, including collagen birefringence, can impact diagnostic accuracy.