IgM nephropathy: clinical picture and pathological findings in 36 patients.

Immunoglobulin M nephropathy (IgMN) is an idiopathic glomerulonephritis characterized by a variable degree of mesangial hyper- cellularity and diffuse IgM deposits. This study describes the clinical presentation and the morphological findings in 36 patients, five adults and 31 children, with IgMN. The initial manifestations of the disease were the nephrotic syndrome in 32 patients, proteinuria in two, hematuria associated with proteinuria in 16 and isolated recurrent gross hematuria in two patients. The nephrotic syndrome was steroid responsive in 9% of the cases, steroid dependent in 25% and steroid resistant in 66%. Five patients were hypertensive at the onset of the disease. The mean follow- up period was 3.4 years (range, 1-7 years). One patient developed end- stage kidney disease five years after the diagnosis. On light microscopy, 24 specimens showed mild focal and segmental mesangial hyper- cellularity, 10 cases were normal in cellularity and two cases showed diffuse global mesangial hyper- cellularity. Four cases showed focal and segmental glomerulosclerosis. Mild interstitial inflammation and fibrosis were observed in 11 cases and focal tubular atrophy and hypertensive hyaline arteriosclerosis were noted in three cases. In addition to IgM, the immunofluorescence study showed C3 deposits in 12 cases, IgG in nine cases and IgA in one case. Electron dense- deposits in the mesangium and para- mesangial areas were demonstrated on electron microscopy in 22 cases. In view of its different clinical presentations and the constant findings of diffuse mesangial IgM deposition in all the cases, it is concluded that this form of nephropathy constitutes a distinct entity separate from minimal change disease or focal and segmental glomerulosclerosis. Patients with IgMN had a higher prevalence of steroid resistance and dependence in the proteinuric group.