Aim: Comparison of clinical and pathological features of secondary IgA nephropathy of ankylosing spondylitis (SIgAN-AS) and primary IgA nephropathy (PIgAN).
Materials and methods: Clinical characteristics and pathological data of patients diagnosed with IgAN by renal biopsy were collected in our hospital from January 2008 to October 2018. Patients with SIgAN-AS and PIgAN were recruited at a ratio of 1 : 5. Fifteen patients with SIgAN-AS and 75 patients with PIgAN were enrolled in this retrospective study.
Results: There were 15 cases in the SIgAN-AS group, including 13 males and 2 females. The cohort of 75 patients with PIgAN included 37 males and 38 females. There were significantly more males in the SIgAN-AS group 13/15 (86.67%) vs 37/75 (49.30%), p < 0.05. Compared with PIgAN patients, SIgAN-AS patients had higher incidences of hematuria (12/15 (80.00%) vs. 37/75 (49.33%), p < 0.05), lower levels of 24-hour urinary protein (0.85 ± 0.68 vs. 1.57 ± 1.54 g, p < 0.05), but higher levels of estimated glomerular filtration rate (eGFR) (CKD-EPI formula; 112.56 ± 24.53 vs. 88.23 ± 29.39, p < 0.05), albumin (44.67 ± 3.48 vs. 41.09 ± 7.07 g/L, p < 0.05), erythrocyte sedimentation rate (ESR) (43.20 ± 33.94 vs. 18.79 ± 16.26 mm/h, p < 0.001), and C-reactive protein (CRP) (21.19 ± 30.61 vs. 2.11 ± 4.58 mg/L, p < 0.001). From the perspective of renal pathology of PIgAN, patients with SIgAN-AS had a lower incidence of renal tubular atrophy/interstitial fibrosis of nephropathy (p < 0.05). Immunohistostaining analysis showed a higher incidence of dominant deposits of single IgA in the mesangial cell area (p < 0.05).
Conclusion: SIgAN-AS was more commonly observed in males and displayed a milder progression than those PIgAN. The majority of SIgAN-AS patients can be improved by early intervention.