The clinical significance of serum free light chain in primary systemic amyloidosis

OBJECTIVE: To evaluate the diagnostic and therapeutic significance of serum free light chain (sFLC) in primary systemic(AL) amyloidosis. METHODS: Twenty-five patients with AL amyloidosis, including 18 men and 7 women with a mean age of 54 (47 - 77) years old, were enrolled from October, 2005 to May, 2010. sFLC was measured by immunoturbidimetric assay. The type of monoclonal light chain was judged upon sFLC κ/λ and its sensibility was compared with serum immunofixation and immunohistochemical analysis. Four patients were treated with M(T)D (melphalan/thalidomide,and dexamethasone), one with VD (velcade and dexamethasone) and four with high-dose melphalan followed by autologous stem cell support. The changes of sFLC were serially determined before and after treatment. RESULTS: Among the 25 patients with AL amyloidosis, two were κ light chains of precursor protein and 23 were λ light chains. Mean plasma cell in bone marrow was 3.5% (0 - 15%). Nineteen (76%) patients had abnormal elevated sFLC and abnormal κ/λ ratios, and 17(68%) patients with immunofixation positive. The sFLC test had similar sensitivity as serum immunofixation (P = 0.727). Twenty-one (84%) patients were shown to have either κ or λ immunoreactive amyloid deposits on biopsied tissues. The sFLC test combined with serum immunofixation allowed the M protein to be detected in 22 (88%) patients. The positive rates of immunohistochemical analysis combined with sFLC test and/or serum immunofixation were 96%. Four patients with hematologic response showed obvious improvement in visceral organ involvement, but illness of 5 patients without hematologic response kept stable or progressed. CONCLUSIONS: sFLC test is a sensitive qualitative and quantitative method to detect M protein. Preliminary data show the patients with obvious sFLC level decrease and/or κ/λ recovery to normal may have a high percentage of improved organs function. sFLC is critical index in diagnosing AL amyloidosis, which might help efficacy assessment.