Antineutrophil Cytoplasmic Autoantibody-Associated Vasculitis with Kidney Involvement in a Patient with AL Amyloidosis

AA amyloidosis With Ig-Dominant Staining and Diagnostically Unusual Features

Introduction

Although serum amyloid A (AA) amyloid may occasionally show nonspecific staining by immunofluorescence (IF), the correct diagnosis can usually be determined by integrating pathologic features and clinical scenario, and using AA amyloid immunohistochemistry (IHC) and/or mass spectrometry. A recent mass spectrometry-based study described false-positive Ig IF staining in a subset of AA amyloid cases.

Methods

We sought to delineate clinicopathologic features of AA amyloid with Ig-dominant staining by using a retrospective review.

Results

AA amyloid with Ig-dominant staining was identified in 10 patients from 5 institutions, representing 1.2% to 4% of AA amyloid kidney biopsies. Evidence of a monoclonal protein was documented in 0% to 2.7% of patients with AA amyloid screened for inclusion, but 30% of those with Ig-dominant staining. The patient population had equal sex distribution and presented at median age of 68.5 years with nephrotic proteinuria and kidney impairment. Etiologies of AA amyloid included injection drug use (30%), autoimmune disease (20%), and chronic infection (10%); 40% had no identified clinical association. On biopsy, heavy chain (co)dominant staining by IF (in 80%), discordant distribution in Ig staining (in 20%), tubulointerstitial nephritis (in 30%), and/or crescents (in 10%) were present. Two of 3 patients with paraproteinemia had concordant heavy and/or light chain dominant staining within the AA amyloid. Two cases were initially misdiagnosed as Ig-associated amyloidosis.

Conclusion

We describe the morphologic spectrum of AA amyloidosis with Ig-dominant staining which may have clinical, laboratory, and pathologic overlap with amyloid light chain (AL), amyloid heavy chain, and heavy and light chain (AHL) amyloidosis.

Proteinase 3 Antibody and Anti-Double-Stranded DNA in a Patient With Immunoglobin Light Chain Amyloidosis

Proteinase 3 (PR3) anti-neutrophil cytoplasmic antibodies (ANCA) and anti-double-stranded DNA (anti-dsDNA) antibodies have been associated with a variety of nephritic diseases, most recognizably granulomatosis with polyangiitis and systemic lupus erythematosus (SLE) glomerulonephritis, respectively. We report the first clinical case of positive PR3 and dsDNA in a patient with renal Immunoglobin light chain (AL) amyloidosis. A 75-year-old man presented to the hospital with chronic fatigue, weight loss, and a recent diagnosis of left ventricular infiltrative cardiomyopathy secondary to AL amyloidosis. Autoimmune serology was significant for PR3-ANCA and anti-dsDNA antibodies. A renal biopsy confirmed AL amyloidosis with diffuse Congo red stain. This case report is the first of its kind, showing atypical antibody presentation in the setting of amyloidosis.