The Subcutaneous Fat Aspirate: A Controlled and Blinded Evaluation of the Technique in the Diagnosis of Primary Amyloidosis (AL)
We performed subcutaneous fat aspiration in 82 patients with biopsy-proven primary amyloidosis and 72 normal adult volunteers. All 154 specimens were randomly sorted and submitted blind to two pathologists for interpretation. Neither pathologist was aware of the number of patients or controls or the interpretation of the other. of the 72 controls, 71 were interpreted as negative; and 1 was interpreted as weakly positive by each. of the 82 amyloid patients, 59 (72 percent) were interpreted as positive by pathologist #1; and 65 (79 percent) by pathologist #2. The concordance rate between the two in amyloid patients was 93 percent. The fat aspirate diagnosed amyloidosis in patients with nephrotic syndrome, heart failure, and neuropathy with equal accuracy. Only patients with carpal tunnel syndrome had a low prevalence of positives (17 percent). The fat aspirate was as sensitive as rectal biopsy (69 percent) and more sensitive than bone marrow biopsy (49 percent). Only renal biopsy was more sensitive than the fat aspirate (97 percent). This procedure could be done by trained technical personnel. One problem was nonspecific birefringence caused by overstaining of slides with Congo red and was responsible for the false positive controls. The fat aspirate does not replace other non-invasive tests but can reduce the necessity of invasive biopsy procedures. There were six instances in which a fat aspirate would have obviated the need for a more invasive biopsy such as heart, kidney, or sural nerve. The fat aspirate is a valuable cost-effective technique in the diagnosis of systemic amyloidosis.
KeywordsNephrotic Syndrome Carpal Tunnel Syndrome Bone Marrow Biopsy Sural Nerve Rectal Biopsy
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