Search

Background: Chronic metabolic acidosis in distal renal tubular acidosis (RTA) has been implicated in the pathogenesis of enhanced bone resorption and osteopenia, resulting in a loss of bone mineral content. However, histomorphometric and bone densitometric studies of patients who suffered from long-standing distal RTA have rarely been done., Methods: A cross-sectional study to determine the alterations of bone mineral density (BMD) and histology was done in 14 nonazotemic RTA patients (11 females and 3 males) who had never received alkaline therapy before enrolling into this study. The mean age was 32.7 +/- 11.9 years. BMD measurements and transiliac bone biopsy were done in all patients. Blood chemistries, intact parathyroid hormone level, and a 24-hour urine collection for the determination of urinary calcium, phosphate, sodium, and potassium were obtained from the RTA patients at the time of bone biopsy. Data from 28 age-, sex-, and body mass index-matched, normal controls who were residents in the same area were also obtained., Results: Urinary excretion of calcium was 2.05 +/- 1.59 mmol/day. No patient had hypercalciuria. The serum intact parathyroid hormone level was 15.92 +/- 8.48 pg/mL. RTA patients had lower BMD in most areas when compared with normal controls. There were two patients who suffered from a pathologic fracture at the femur. Bone histomorphometry from RTA patients shows a significantly decreased bone formation rate (0.02 +/- 0.02 vs. 0.07 +/- 0.045 microm(3)/microm(2)/day, P < 0.05), not significantly decreased osteoblastic surface (0.78 +/- 1.03% vs. 2.6 +/- 1.1%) and osteoclastic surface (0.05 +/- 0.03 vs. 0.13 +/- 0.23%), but significantly increased osteoid surface (31.47 +/- 24.52 vs. 5.79 +/- 4.39%, P < 0.05) and osteoid volume (2.95 +/- 3.09 vs. 0.92 +/- 1.05%, P < 0.05) when compared with those of normal controls. There was no difference in osteoid thickness (10.65 +/- 6.10 vs. 8.69 +/- 2.14 microm). Only one distal RTA patient who had a marked increase in osteoid thickness justified the diagnosis of osteomalacia., Conclusions: This study demonstrates that low bone mass is common in distal RTA patients. Chronic metabolic acidosis results in suppression of bone formation and resorption, which in turn may contribute to the development of low bone mass in distal RTA patients. Although minor elevations in osteoid surface and osteoid volume are found among distal RTA patients, overt osteomalacia is not the predominant bone lesion.

Unlabelled: The spectrum and clinical relevance of renal osteodystrophy in Thai dialysis patients are unknown. A study was conducted on the prevalence and clinico-pathological correlation of renal osteodystrophy in chronic dialysis patients who attended Ramathibodi Renal Transplant Clinic between September 1996 and March 1998. All possible volunteers were enrolled irrespective of musculoskeletal symptoms. Fifty six dialysis patients, including 17 (30.4%) CAPD and 39 (69.6%) hemodialysis patients, participated in this study. Serum calcium, phosphate, iPTH, and bone specific alkaline phosphatase were determined. Transiliac crest bone specimens were measured with an average of 30 fields/specimen by a specific computer program for bone histomorphometry (Osteomeasure), and were also studied for dynamic by double tetracycline label. Bone mineral density (BMD) was also determined by DEXA scan. The type of bone pathology was based on Fournier's criteria for renal osteodystrophy. The mean +/- SEM for age was 45.52 +/- 1.74 years, dialysis duration 42.26 +/- 5.54 (range 1-156) months, calcium phosphate product 52.31 +/- 2.77, and iPTH 307.73 +/- 62.04 pg/ml. The following types of renal osteodystrophy were found: adynamic bone 23 (41.1%), hyperparathyroid 16 (28.6%), mixed type 11 (19.6%), mild lesion 3 (5.4%), osteomalacia 2 (3.6%), and osteosclerosis 1 (1.8%) cases. Two cases of aluminum related bone disease were found. The distribution of different bone diseases was not affected by mode of dialysis or vitamin D supplement, but it was affected by dialysis duration. High turnover bone diseases were associated with longer dialysis duration (63.19 +/- 8.9 vs 23 +/- 4.73 months), higher iPTH (541.53 +/- 109.32 vs 87.77 +/- 15.76 pg/ml), and higher bone specific alkaline phosphatase (25.43 +/- 5.04 vs 9.62 +/- 1.34 mg/ml) when compared to low turnover bone diseases, p < 0.05. Intact PTH of greater than 200 pg/ml was a good predictor for high turnover bone diseases (74% sensitivity and 96% specificity). BMD at torch and wards areas varied inversely with dialysis duration (r = -0.3 and r = -0.4, respectively; p < 0.05). Chronic dialysis patients had a greater tendency of bone loss compared to the general Thai population. There was no difference in BMD between CAPD and hemodialysis patients or different types of bone lesions., Conclusion: Significant bone diseases are common among Thai chronic dialysis patients. Adynamic bone disease is the most common bone lesion followed by hyperparathyroid and mixed type. The spectrum of bone diseases is affected mainly by dialysis duration. Intact PTH is a good predictor of high turnover bone disease. Greater bone loss than in the general population is common in our patients and is also accentuated by longer dialysis duration.