Clinical and immunopathologic study of mesangial IgM nephropathy: report of 41 cases

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Abstract
Of 408 cases, 41 (or 10%) of primary glomerular disease had diffuse fine granular to arc-like short linear mesangial deposits of IgM. The IgM deposition was accompanied by C[complement component]1q and/or C4 in 29 cases, by C3 in 10, and by trace amounts of IgA in 6. Properdin-factor B was not detected. Fine granular electron dense deposits of low density were detected in the mesangium in all 41 cases, usually as a discrete pattern beneath the mesangial glomerular basement membrane and correlated well with the immunofluorescence findings. An immune complex disease with complement activation is suggested. The ages of the patients varied from 2 to 58 yr (average 23.8 yr). A male predominance of 2.2:1 was identified. Serum IgM level was elevated in 46.7% of the cases. Most cases (87.8%) manifested a nephrotic syndrome or relapse at biopsy, and the remaining cases experienced proteinuria. Among the 36 nephrotic patients, 22 cases (61.1%) demonstrated complete remission with steroid therapy, 9 cases (25%) were resistant, and 5 cases (13.9%) had partial remission. Remission were later achieved with cytotoxic drugs or methylprednisolone pulse therapy in 3 and 4 cases, respectively, in the steroid resistant patients. Frequent relapses occurred during the course in 22 of 32 cases (68.8%) who had experienced complete or partial remission. Sustained complete remission was achieved with prednisolone with or without therapy in only 14 (42.4%) of the 33 nephrotic cases followed up for > 6 mo. Pathologically, 56.1% of the patients showed mild to moderate increase in mesangial matrix and cellularity. Focal and segmental sclerosis was demonstrated in 4 cases (9.8%). Minimal glomerular change was also common (34.1%). The patients with minimal change seemed to have a higher complete remission rate than patients with more evident glomerular alterations. Mesangial IgM nephropathy is an important disease in Taiwan, with a variable response to treatment and frequent relapses. During follow-up periods of .ltoreq. 3.5 yr, no deterioration of renal function occurred. The relationship between this disease and focal glomerulosclerosis deserves further investigation.