The study aimed to investigate the influence of shrunken pore syndrome (SPS), defined as a cystatin C (CysC)-based estimated glomerular filtration rate (eGFRCysC) <60% of the creatinine (Cr)-based eGFR (eGFRCr), on bone mineral density (BMD) in patients with rheumatic diseases. A total of 831 patients with rheumatic diseases were enrolled in the study. Patients were classified into the SPS group (G-SPS) and non-SPS group (G-nSPS). The correlation between the presence of SPS and BMD of the lumbar spine (BMD_LS), BMD of the femoral neck (BMD_FN), serum parathyroid hormone (PTH) level, chronic kidney dysfunction (CKD), and parameters were evaluated statistically. The prevalence of SPS was 4.0%. Serum PTH level, tartrate-resistant acid phosphatase-5b (TRACP-5b), and eGFRCr in the G-SPS were significantly higher than in the G-nSPS, whereas BMD_LS and BMD_FN in the G-SPS were significantly lower than in the G-nSPS. Serum PTH level was significantly correlated with CysC. BMD_LS had no significant correlation with BMD_FN. The presence of SPS was the only factor that demonstrated significant negative correlation with both BMD_LS and BMD_FN. Relationship between BMD_LS and the presence of SPS was present regardless of CKD stage; however, the negative relationship between BMD_LS and serum PTH was observed only in CKD stage 1 and 2 patients. BMD_FN demonstrated significant negative correlation with serum PTH in the group with progression of CKD. These results suggest that there is a serious potential risk of osteoporosis in patients with SPS and increased PTH, and BMD_LS poses a higher risk in CKD stage 1 and 2.
Keywords: Chronic kidney diseases; bone mineral density; calcium metabolism; cystatin C; parathyroid hormone; shrunken pore syndrome.