This multicenter observational study is the first and the most comprehensive one regarding the epidemiologic data of patients with MCD in Turkey. Adult-onset MCD comprised 6% (233/3875) of the entire primary glomerulonephritis database. The median age was 35.0 (26.0-50.5) years, and 59.7% were under 40 years of age. Renal biopsy was performed in 196 (84.1%) patients due to nephrotic syndrome. Compared to the group under 40 years of age, chronic changes were more common in the group aged ≥40 years.
In minimal change disease, the glomeruli are pathologically normal in the light microscope and there are no complement or immunoglobulin deposits in the immunofluorescent microscope. The characteristic histological lesion that can only be seen on electron microscopy is diffuse effacement of epithelial foot processes. There are three other disorders that usually present with the nephrotic syndrome and that may show only minor changes on light microscopy: idiopathic mesangial proliferative glomerulonephritis, immunoglobulin M (IgM) nephropathy, and C1q nephropathy. These disorders may represent variants of MCD or FSGS (3,4.10)
The frequency of MCD among primary glomerulonephritis in adults was determined as 9.1% in the study by Malafronte et al. (11), and 0.9% in Li et al. (12). In our study, it was found to be 6.0%.
In a retrospective analysis of 95 adult patients with MCD, at presentation, Waldman et al. (13) found a median age 45 years, serum creatinine 1.4 mg/dl, eGFR 72 mL/min/1.73 m2, proteinuria 9.9 g/day, hematuria 29%, serum albumin 2.2 g/day, serum cholesterol 421 mg/dL and hypertension 43%. Huang et al. (14) evaluated 46 Chinese patients diagnosed with adult MCD by biopsy in their retrospective study. The male to female ratio was 1.2:1. The mean age of onset was 30.9 years, and 80% of the patients with MCD were less than 40 years. The mean daily proteinuria was 10.2 g, and serum albumin was 1.8 mg/dl. Azotemia occurred in 16 (35%) of 46 cases; hypertension, 13%; and microscopic hematuria, 13%. In another study, the male to female ratio was found to be 1:1.4, with a mean age of 37 years. At presentation, hypertension was found in 47% of patients, microscopic haematuria in 33%, hypercholesterolemia and hypertriglyceridemia in 96% (15). In a study conducted in England, 89 patients were examined, the mean age was 42, the male-female ratio was 1.28:1, the average albumin was 2.0 g/dl, nephrotic syndrome was found in 73%, and microscopic hematuria was found in 28.3%. Hematuria was more frequent in patients aged more than 45 (13 of 32) than in younger patients (7 of 41) (P < 0.05) (16). In our study, the median age of the patients was 35.0 (26.0-50.5) years, creatinine 0.7 (0.6-1.0) mg/dl, proteinuria 6000 (3110-9213) g/day, triglyceride 203 (126-301) mg/dl, mean serum cholesterol 350±139 mg/dl and albumin 2.6±1.0 g/dl detected. Hypertension was found in 25.3% of the patients and hematuria in 19.3% of the patients. The male to female ratio was 1.16:1. 59.7% of our patients were under the age of 40. The eGFR of 30 (12.9%) patients was below 60 ml/min/1.73m2. Nephrotic syndrome was found in 84.1% of the patients and microscopic hematuria was found in 19.3% of the patients. There was no difference between age groups in terms of proteinuria level and microscopic hematuria.
Tse et al. (17) evaluated 50 adult MCDs in their study, and the mean age was 48.3±18.1 years, and the patients were divided into two groups as under 50 years old and over. Serum creatinine was found to be high ((p=0.007)) and creatinine clearance was found to be significantly lower (p=0.003) in the 50 years and older group. In our study, creatinine was found to be higher (0.8 vs. 0.7 mg/dl, p<0.001) and eGFR was significantly lower (83 vs. 119 ml/min/1.73m2, p<0.001) in the ≥40 age group compared to the <40-year-old group.
There are some racial differences in the prevalence and prognosis of idiopathic nephrotic syndrome. The Asian adult-onset MCD had younger age and male predominance in comparison to those of the Western population (14). In our study, the number of men was higher, and the median age of onset of disease was 35 years, and it was between the Western and Asian populations.
In a study performed in Japan, 62 adults MCDs were evaluated. All renal biopsy specimens contained an average of 19.8±1.3 glomeruli/specimen. Global sclerosis was detected in 14 (22.6%) of the patients, and mesangial hypercellularity was found in 35 (56.4%) patients. Weakly positive immunofluorescence (IgG or IgM) was found in 19 (30.6%) patients (18). Similarly, in our study, the median glomeruli count was 17.0 (10.0-25.0). Global sclerosis was detected in 67 (28.7%) of the patients, and mesangial hypercellularity was found in 65 (27.9%) patients. Similarly, weak positive immunofluorescence (IgG or IgM) was found in 67 (28.7%) patients.
Histologically, MCD is characterized by normal-appearing glomeruli by light microscopy and the absence of complement or immunoglobulin deposits by immunofluorescence microscopy (3, 4). In our study, in immunofluorescence microscopy, IgA, IgM, IgG, C3 and C1q staining were detected in 14 (6.0%), 57 (24.5%), 12 (5.1%), 38 (16.3%) and 12 (5.1%) patients, respectively. There was no difference in immunofluorescence staining between the groups below and above 40 years of age. Compared to the group under 40 years of age, chronic changes were more common in the group aged 40 and over. Global sclerotic glomeruli (17.2% vs. 45.7%), interstitial fibrosis (14.4% vs. 33.0%), vascular changes (7.2% vs. 26.6%), tubular atrophy (12.9% vs. 31.9%) were more common in patients ≥ 40 years of age.
IgM deposits may be found in patients with MCD, focal segmental glomerulosclerosis (FSGS), and mesangial proliferative glomerulonephritis. Some experts, however, believe that IgM nephropathy is a distinct entity characterized by mesangial proliferation and prominent mesangial deposits of IgM and complement. Debate remains as to the clinical significance of IgM deposition in glomerular disease (11). In our study, in immunofluorescence microscopy, IgM staining (weak) was detected in 57 (24.5%) patients. There were no clinical and laboratory differences in IgM positive patients.
Our study had some limitations. First, our study did not reveal data regarding the prognosis of patients with adult-onset MCD. Second, because biopsies are analyzed by different pathologists, the data may not be completely homogeneous. In addition, an electron microscopic examination was not performed in all cases, and, hence, it was not presented in the manuscript. However, the data presented by the Turkish Society of Nephrology Glomerular Diseases Study Group represent the histological findings in patients with MCD, despite differing interpretations among different pathologists and different biopsy policies and histopathological findings. Our database, which includes a large number of kidney biopsies, presents important findings considering our geographical location.