Monoclonal Ig deposition disease (MIDD) is a rare complication of
monoclonal gammopathy characterized by deposition of monoclonal
Ig light chains and/or heavy chains along the glomerular and tubular basement membranes. Here, we describe a unique case of
IgD deposition disease.
IgD deposition is difficult to diagnose, because routine immunofluorescence does not detect
IgD. A 77-year-old man presented with
proteinuria and
renal failure, and kidney biopsy analysis showed a nodular sclerosing GN with extensive focal global glomerulosclerosis, tubular
atrophy, and interstitial
fibrosis. Immunofluorescence was negative for Ig deposits, although electron microscopy showed deposits in the glomeruli and along tubular basement membranes.
Laser microdissection of glomeruli and mass spectrometry of extracted
peptides showed a large spectra number for
IgD, and immunohistochemistry showed intense glomerular and tubular staining for
IgD. Together, these findings are consistent with
IgD deposition disease. Bone marrow biopsy analysis showed 5% plasma cells, which stained for
IgD. The patient was treated with
bortezomib and
dexamethasone, which resulted in improvement of hematologic parameters but no improvement of renal function. The diagnosis of
IgD deposition disease underscores the value of
laser microdissection and mass spectrometry in further evaluating renal biopsies when routine assessment fails to reach an accurate diagnosis.