Abstract
ObjectivesSkin fat biopsy of the abdominal wall is a simple and safe method for detecting amyloidosis, and rectal mucosal biopsy is also frequently used for screening for the disease; however, the sensitivity of these approaches has not been fully studied. The aim of this study was to evaluate the efficacy of skin fat biopsy combined with rectal mucosal biopsy as a screening procedure for the diagnosis of systemic immunoglobulin light-chain (AL) amyloidosis.MethodsWe retrospectively analyzed 224 AL amyloidosis patients confirmed by renal biopsy, including a test group of 165 patients and validation group of 59 patients. Surgical skin fat biopsy from the abdominal wall and rectal mucosal biopsy under endoscopy was performed to obtain specimens. Congo red staining and immunofluorescence staining with antibodies against light chains were performed to type the disease. Pathology reports were reviewed to assess the diagnostic sensitivity of skin fat biopsy and rectal mucosal biopsy. Diagnostic specificity was not examined in the present study, because no healthy volunteers and only few patients with other diseases had performed immunofluorescence staining on skin fat and rectal specimens.ResultsOf the 165 patients in the test group, Congo red staining of skin fat and rectal mucosal specimens was associated with a sensitivity of 89.3% and 94.8%, respectively. The sensitivity increased to 98.9% by combining both biopsy methods. Immunofluorescence stains were positive in 81.1% of patients undergoing skin fat biopsy and 84.7% of patients undergoing rectal mucosal biopsy. Immunofluorescence stains yielded positive results in 86.7% of cases combining skin fat biopsy with rectal mucosal biopsy. The diagnostic results also performed well in the validation group.ConclusionsSurgical skin biopsy including the subcutaneous fat pad can be performed safely at the bedside and is useful for diagnosing AL amyloidosis. Combining skin fat biopsy with rectal mucosal biopsy may identify amyloid deposits in almost all patients, and a negative result of both biopsies makes the diagnosis very unlikely.
Highlights
Of the 165 patients in the test group, Congo red staining of skin fat and rectal mucosal specimens was associated with a sensitivity of 89.3% and 94.8%, respectively
The sensitivity increased to 98.9% by combining both biopsy methods
Immunofluorescence stains were positive in 81.1% of patients undergoing skin fat biopsy and 84.7% of patients undergoing rectal mucosal biopsy
Summary
AL amyloidosis, caused by the extracellular deposition of fibril-forming monoclonal immunoglobulin light chains secreted from neoplastic plasma cells or B cell clones, is the most common type of systemic amyloidosis, with an incidence of 8.9 per million person-years [1, 2]. Biopsies of the involved visceral organs have a high sensitivity for detecting amyloid deposition; such invasive procedures may carry significant risks, including hemorrhage and arrhythmia [5]. Subcutaneous fat aspiration (SFA) is a safe, simple, and low-cost method for obtaining tissue to diagnose systemic amyloidosis with a sensitivity of 67–93% [8,9,10]. To obtain adequate tissue samples for accurate diagnosis and classification, surgical skin biopsy including the subcutaneous fat pad has been applied in our center. It can be performed safely at the bedside with high sensitivity
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