Amyloidosis and Plasma Cell Dyscrasias: A Single Institution Experience

Background:

Amyloidosis is the extracellular tissue deposition of small molecular subunits of proteins as fibrils. AL Amyloidosis is a complication of underlying plasma cell dyscrasia with an associated monoclonal paraprotein. It can occur in association with multiple myeloma (MM), Waldenstrom macroglobulinemia (WM) or non-Hodgkin lymphoma. While isolated organ involvement can be seen, many patients (pts) have multiorgan involvement. Our aim was to explore the trend of amyloidosis associated with plasma cell dyscrasia, treatment and outcome at our institution.

Methods:

After IRB approval, we reviewed medical records of adult pts ≥ 18 years with a histological diagnosis of amyloid and had evidence of monoclonal gammopathy, between January 1^st, 2010 and June 30^th, 2019. We reviewed age at diagnosis, gender, work up for paraproteinemia, site of biopsy, technique used for identification of amyloid, imaging studies, treatment and outcome.

Results:

We found a total of 33 pts with biopsy proven amyloid and evidence of a monoclonal paraprotein. 23 (69.6%) were males and 10 (30.3%) were females. Age ranged from 39 to 89 years with a median age of 62; 3 (9%) being <50 years. 7 (21.2%) were diagnosed with multiple myeloma and one pt each was diagnosed with diffuse large B cell lymphoma and WM.

Monoclonal paraprotein was IgG Kappa in 10 (30.3%), IgG lambda in 5 (15%), IgA lambda in 3 (9%), IgA kappa in one, IgM lambda in 3 (9%), IgM Kappa in one, kappa light chain in 5 (15.1%), lambda light chain in 3 (9%), one had both IgG lambda and IgM kappa and no paraprotein was documented in one pt. Serum protein electrophoresis with immunofixation was positive in 22 (66.6%), Urine protein electrophoresis and immunofixation was positive in 16 (48.4%).

Most common initial site of amyloid identification by biopsy was kidney in 12 (36.3%). Diagnosis was from abdominal fat pad in 8 (24.2%), lung in 4 (12.1%), bone marrow, heart and skin in 2 each (6%) and liver, colon and bone in 1 each (3%). Positive immunohistochemistry (IHC) stain demonstrating light chain restriction was seen in 23 (69.6%) and out of this only 11 (33%) underwent further evaluation with mass spectrometry. One patient with positive IHC had negative mass spectrometry despite high clinical suspicion for AL amyloidosis. IHC was not performed in 8 (24.2%) and identification was only based on Congo red staining. IHC was negative in 2 (6%) despite evidence of a monoclonal paraprotein.

Involvement of kidney was identified in 14 (42.4%) with isolated kidney involvement in 2 (6%). Cardiac involvement was identified in 17 (51.5%) either by biopsy, imaging findings and/or pro-BNP and troponin levels and isolated cardiac disease was noted in 3 (9%). 6 (18.1%) had lung involvement, which was the only disease site in 4 (12.1%). Neuropathy was noted in 10 (30.3%). One had only a single bony site involved.

21 (63.6%) were treated with disease related therapy for amyloidosis, one patient underwent radiation to site of isolated bone disease and the remaining patients were either observed or died before therapy was initiated. 7 (21%) underwent Autologous stem cell transplant for amyloidosis. At the time of data cut off, 21 (63.6%) were alive and 12 (36.3%) were deceased. Amyloidosis was the documented cause of death in 10 pts and of this 9 pts had cardiac involvement.

Conclusion:

AL Amyloidosis is an uncommon disorder and patients should undergo further diagnostic evaluation if suspicious symptoms with an underlying monoclonal gammopathy. In our study, we noted a male predominance and IgG Kappa was the most common monoclonal paraprotein. As immunohistochemistry has a greater chance of false positive and false negative results, mass spectrometry is the preferred method for identification of amyloid. However, this technique is not widely available which restricts it's use in clinical practice. In our study, we identified one patient with positive IHC who had negative mass spectrometry despite high clinical suspicion for AL amyloidosis. We also identified two patients with negative IHC despite evidence of a monoclonal paraprotein and this may be either a false negative IHC or the amyloid being unrelated to the monoclonal paraprotein. 9/10 pts who died of amyloidosis had cardiac involvement.