Patients with IgA nephropathy have various clinical manifestations from mild symptoms such as microscopic hematuria, proteinuria, edema, hypertension to severe symptoms like rapidly progressive glomerulonephritis that need renal replacement therapy [6,7,8]. Microscopic hematuria and proteinuria were the most common manifestations of IgA nephropathy in Japanese patients because of the routine urinalysis screening in Japan [6]. In Korea, IgA nephropathy was found as the second most common pathological finding in children who underwent renal biopsy with clinical hematuria [9]. Although in Thailand, we do not have routine urinalysis screening, microscopic hematuria was still the most common clinical manifestation in IgA nephropathy.

The main drugs of choice for IgA nephropathy are angiotensin-converting enzyme inhibitor and corticosteroid for patients who have significant proteinuria [7, 10]. Earlier studies supported that corticosteroid was associated with the improvement in clinical outcomes [10]. As in our study, clinical outcomes including hypertension, edema, hematuria, and proteinuria improved at 12 months after treatment. Sean J. Barbour et al. [11] showed median eGFR at biopsy was 98 ml/min per 1.73 m2 with decreased proteinuria. The progression of IgA nephropathy was typically slow. In our study, 24% of patients developed chronic kidney disease in 2 years from diagnosis. One study showed that 10–13% of children will reach end-stage renal disease(ESRD), and within 20 years, 20–30% would have ESRD [8].

The clinicopathologic correlation in IgA nephropathy especially with MEST-C scores becomes a useful information to predict renal outcomes and for effective management decisions. This study found that mesangial hypercellularity and segmental glomerulosclerosis were frequent renal pathological findings in children with IgA nephropathy. The study from children also reported the similar results that segmental sclerosis/adhesion lesion (62%) and mesangial proliferation (45%), were found as major findings [4]. These results were in contrast to adult patients, from the Oxford classification study that had shown the amount of endocapillary hypercellularity was more frequent, whereas tubular atrophy/interstitial fibrosis was less frequent among pediatric patients compared to adults [12].

The variation in clinical symptoms of IgA nephropathy can provide a clue for renal pathology. Oxford classification 2016 [3] has been a reference point in our study. Our study showed that microscopic hematuria was strongly associated with mesangial hypercellularity which was indicated as an acute glomerular lesion. Moreover, hypertension is a prognostic factor for segmental glomerulosclerosis (S score). Similar result was also shown in previous study that the S score was associated with reduced eGFR and was higher MAP at the time of biopsy [13]. Severe pathological lesions (e.g., S, T, C) were associated with lower eGFR, higher blood pressure, and higher proteinuria, that were consistent with other findings. Glomerular hypertension may mediate progressive renal damage by leading to glomerular hyperfiltration and glomerular enlargement [14]. The previous study showed S lesion was associated with more proteinuria at presentation and more rapid decline in renal function [4]. In our study, tubular atrophy/interstitial fibrosis, and crescents lesions showed significant association with nephrotic range proteinuria in univariate Cox analysis, but it failed to attain independent significance in a multivariate model. As well as the crescent lesion was significantly associated with rapidly progressive glomerulonephritis and hypertension in univariate Cox analysis, but it was not in a multivariate model.

The presence of M1 or S1 was a histological marker predicting the benefits of steroid therapy [15]. In our study, more than half of patients that mostly had M1 and S1 scores on renal pathology received corticosteroids. After treatment follow-up, the mean serum creatinine and eGFR had not changed. In pediatric IgA nephropathy, the attempts to validate the value of MEST-C scores have always faced the problems of too few endpoints (50% decline in eGFR or ESRD) in cohorts with only a few hundred cases, and a median follow-up of 5–10 years, that is insufficient to detect a functional decline in cases with early diagnosis. As expected, T lesions are the strongest risk factors for progression in children as well as in adults, but using only a T score for selecting the treatment may be only a caution in aggressive therapy when fibrotic changes are too extensive [16]. We also found a strong correlation between T score and immunosuppressive drug use. The intensive treatment was used more in the patients with tubular atrophy/interstitial fibrosis lesion on renal biopsy than other lesions from MEST-C scores.

The presentation of crescent formation correlated with using an immunosuppressive drug such as cyclophosphamide [3]. Our study showed a similar result that pulse methylprednisolone and cyclophosphamide were used significantly more in patients with crescentic lesions than in other lesions.

The previous study has mentioned that the E lesion was not predictive of the outcome but associated with treatment. Presenting E1 were more likely to receive immunosuppressive therapy [4], most frequently corticosteroids [3]. This contrasts with our study that E lesion alone was not related to immediate treatment. In fact, the significant correlation with the treatment decisions in the short-term outcomes among the study population were mainly found in T and C lesions.