Discussion
The majority of MG cases with light chain isotype-restricted deposits lack a recognizable secondary etiology. However, the absence of PLA2R positivity, positive staining for a single IgG subclass, and presence of focal proliferation are worrisome histopathologic features that should prompt a thorough clinical workup to exclude the presence of an underlying LPD.
Methods
We conducted a retrospective analysis of 28 cases of MG that showed light chain isotype restriction.
Results
The mean age at diagnosis was 62.2 years and the male-to-female ratio was 1. All patients presented with proteinuria (73.1% nephrotic range), and the mean serum creatinine was 1.5 mg/dl. Six patients had an underlying lymphoproliferative disorder (LPD), 2 had autoimmune disease, and 1 patient was positive for both hepatitis B and syphilis. Only 1 of the patients with an LPD had a detectable monoclonal Ig. Four patients (14.3%) showed focal proliferation or crescents, 3 of whom had an underlying LPD. Kappa (κ) restriction was seen in 26 of 28 patients (85.7%). Staining for IgG subclasses was performed in 19 cases, 14 of which showed positive staining for a single subclass. PLA2R was positive in 7 of 27 cases. 30% of PLA2R-negative patients and 28.6% of those with positive staining for a single IgG subclass had an associated LPD.