Fine needle aspiration of abdominal fat for the diagnosis of amyloidosis

Amyloidosis is a dysproteinemia characterized by extracellular deposition of amyloid fibrils. Its diagnosis depends on the demonstration of the characteristic apple-green birefringence in tissue stained with Congo red. Aspiration of subcutaneous fat as a means of procuring tissue has received attention in the internal medicine literature. However, this application of fine needle aspiration biopsy has not been investigated extensively by cytopathologists. We therefore report our experience. Over the past two years we performed 18 aspirations of subcutaneous fat on 17 patients in whom amyloidosis was clinically suspected. Eight aspirates were positive for amyloid, and nine were negative. There were no known false-negative results. False positives were more problematic, occurred early in our experience and were due to overinterpretation of occasional long, slender, green strands representing collagen. The true positives were all characterized by large numbers of short, apple-green strands intimately associated with the fat, oriented in multiple directions and occurring in much, if not all, of the aspirated fat. Attention to details of the aspirated material other than the presence or absence of apple-green birefringence can lead to a correct distinction between amyloid and collagen. We conclude that abdominal fat pad aspiration is useful in the workup of suspected amyloidosis, especially since it is a safe, easily performed procedure.