[1682] Immunotactoid Glomerulopathy: Clinicopathologic Study of 16 Cases

Samih H Nasr, Lynn D Cornell, Mary E Fidler, Salwa S Sheikh, Abdulrazack A Amir, Sanjeev Sethi. Mayo Clinic, Rochester, MN; Dhahran Health Center, Dhahran, Saudi Arabia

Background: Immunotactoid glomerulopathy (IT) is a rare GN, tenfold rarer than fibrillary GN. To better define the clinicopathologic spectrum and prognosis of IT, we report the largest series to date.
Design: We identified 16 cases of IT from our pathology archives, between 1993-2011. All cases fulfilled the following diagnostic criteria of IT: glomerular deposition of microtubules that (1) had hollow centers at magnification of <30,000, (2) arranged in parallel arrays; and (3) stained with antisera to immunoglobulins by immunofluorescence (IF). Biopsies with clinicopathologic diagnoses of cryoglobulinemic GN or lupus nephritis were excluded.
Results: All 16 pts were Caucasians with a F:M ratio of 1 and a mean age at diagnosis of 60 yrs (range 41 to 80). Presentation included proteinuria (100%, mean 7.5 g/day), nephrotic syndrome (69%), renal insufficiency (50%, mean serum (S.) creatinine 2.0 mg/dL), and microhematuria (80%). 46% had hypocomplementemia. S. cryoglobulin and HCV antibody were negative. A S. M-spike was present in 63%. Hematologic malignancy was present in 38% of pts, including small lymphocytic leukemia (CLL) in 19%, lymphoplasmacytic lymphoma (LPL) in 12%, and smoldering myeloma in 12%. One pt had LPL and smoldering myeloma. The hematologic malignancy was discovered 1.8-6 yrs before IT diagnosis in 50% of pts and concomitantly with the IT diagnosis in the remaining 50%. The most common glomerular pattern on light microscopy (LM) was membranoproliferative GN (56%, including 31% with segmental membranous features) followed by global membranous GN (31%) and endocapillary proliferative GN (13%). Interstitial lymphomatous infiltration was present in all 19% of pts with CLL. By IF, 88% showed glomerular positivity for IgG, 25% IgM, and 6% IgA; the deposits were single light chain-restricted in 56%. On electron microscopy, the microtubular deposits were seen in the mesangium in 75% of cases, in the subepithelial space in 75% and in the subendothelial space in 75%. The mean microtubule diameter was 31 nm (range of means, 17-52). During a mean of 42 mo of follow-up for 13 pts with available data, 39% had complete or partial remission, 38% had persistent renal dysfunction, and 23% progressed to ESRD. Two-thirds of pts received immunosuppressive (IS) therapy.
Conclusions: IT typically affects older pts. Hematologic malignancy (most commonly CLL) is present in over a third of pts and a circulating paraprotein in two-thirds. LM usually shows membranoproliferative or membranous GN. Over a third of IT pts are expected to recover renal function with IS therapy.
Category: Kidney (does not include tumors)

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 273, Wednesday Afternoon


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