BONE BIOPSY BASED SPECTRUM OF RENAL OSTEODYSTROPHY IN EGYPTIAN HEMODIALYSIS PATIENTS: ALUMINUM SURPRISE

Renal osteodystrophy (ROD) exhibits varying characteristics among different populations. Variable genetic and environmental factors and prescription patterns may explain these differences. Egyptian ROD is not sufficiently studied. Although bone biopsy is the gold standard tool, no single study has reported the actual ROD spectrum based on bone biopsy in Egypt or Africa. International guidelines and recommendations must take into account the distinct patterns in developing countries. Unfortunately, most of the currently available biopsy-based studies explored the ROD nature in developed countries. Exploring the ROD patterns in these poorly represented regions would have a large impact on the future recommendations. As an example, the Japanese Society for Dialysis Therapy sets its own distinct targets and recommendations for serum iPTH level that differ from those outlined by the KDIGO CKD-MBD guidelines. Adhering to these guidelines has led to decreased mortality rates among Japanese patients with CKD.

The ISN-sistership program enabled us to create an Egyptian bone biopsy consortium that provided a nationwide specialized CKD-MBD service. CKD patients were referred to our clinics over the last 2 years after the launch of this service. Those patients were included in our cross-sectional study. Patients were included if they had unexplained bone pain, fractures, osteoporosis, or abnormal CKD-MBD laboratory parameters. Bone biopsies were planned based on clinical indications, including bone pain, osteoporosis, or fractures that are not explained by non-invasive tools. Patients were excluded from the study if they were younger than 18 years, pregnant, or lactating. Patients with active malignancy, uncontrolled thyrotoxicosis, chronic alcoholism, and decompensated chronic liver disease were excluded from the study. Kidney transplant recipients, patients who are allergic to tetracycline, or not willing to give informed consent, were not included. In addition to basic clinical data, the following laboratory tests were done for biopsied patients; serum levels of calcium, albumin, phosphorus, intact parathyroid hormone (iPTH), vitamin D levels, total alkaline phosphatase (ALP), Bone-specific Alkaline Phosphatase (BsAP), Tartrate-Resistant Acid Phosphatase 5b (TRAP5b), sclerostin, Fibroblast Growth Factor 23 (FGF23), klotho and serum aluminum (AL) in addition to DEXA scan. Bone biopsies were processed and analyzed under the supervision of experts from the Division of Nephrology, Bone and Mineral Metabolism at the University of Kentucky, USA. Anterior iliac crest bone biopsies were performed using a vertical approach. Bone specimens were processed without removal of minerals and analyzed using their protocol. 

Biopsy results:

Over 2 years, 14 patients had clinical indications and consented to the bone biopsy; all were on HD. Adynamic bone disease (ABD) was the most common ROD type in our cohort. Unexpectedly, various degrees of positive aluminum staining were present in 93% (13 patients) of the biopsied patients, despite the nonuse of aluminum-based phosphate binders. Only one patient had no aluminum in his bone. He had started dialysis 2 months before the biopsy with significant residual kidney function. All other patients had longer dialysis vintage with a median of 5 years on dialysis. To define a significant amount of aluminum toxicity, 30% of the trabecular bone surface stained with aluminum special stains was used as a cut-off point. Those with 30% or more were identified as the (AL+ve) group, which included the majority of the patients (8 patients - 57%). The (AL-ve) group, which had less than 30% staining, consisted of 6 patients. Other biopsy findings are noted in Table 1 and Figures 1 and 2. 

 Root cause analysis:

Root cause analysis was done, triggering an environmental alarm for potential iatrogenic or environmental aluminum sources. Aluminum-containing antacids or phosphate binders were not used by any of our patients. All patients were using Aluminum-based cocking utensils, which were previously reported to carry a risk of aluminum exposure. This analysis was summarized in Figure 3.

Drinking water source:

Finally, municipal tap water drinking was more common in the (AL+ve) group in comparison to home water filter users. Random samples from their dialysate and drinking water were rechecked, and all were within international standard limits. When analyzing biopsied patients with low turnover states and checking their drinking water sources, 7 patients used municipal tap water and 4 used home water filters. Results were not significant due to the limited number of patients, but the difference is evident as shown in Figure 4. Considering the systematic use of aluminum sulfate in municipal water purification, intermittent aluminum leakage to tap water that is not captured in our screening cannot be excluded.

The pathobiological effect of aluminum:

Aluminum-induced suppression of bone cells was evident by low turnover biomarkers in patients with significant aluminum accumulation. Moreover, FGF-23 levels were significantly elevated in the AL+ group with a median of 2626 pg./mL compared to 1096 pg./mL in the AL- group (p-value = 0.041) as shown in Figure 5.

A literature review was made for the prevalence of biopsy-proven aluminum bone disease in dialysis patients over the last 25 years, to check if this is a national or multinational challenge. Despite the declaration of the extinction of aluminum bone disease based on studies from developed countries and some opinion-based articles, it is still detectable in Brazil. Maybe the explanation is that they are still practicing bone biopsies more liberally. To diagnose aluminum bone disease, you need to do a biopsy and to detect it by specific stains at the mineralization front, as in figure 6. Or to mobilize aluminum from bone by deferoxamine then to measure this complex. Otherwise, aluminum will stay hidden in the bone, leaving low serum levels that cannot diagnose this toxicity alone. Currently, deferoxamine is not available in Egypt as newer iron chelators are replacing it. 

Aluminum bone disease is not extinct yet. Of the biopsied patients, 93% had variable degrees of positive aluminum staining, and 57% had significant aluminum accumulation. These shocking numbers of heavy aluminum deposition should not be generalized to all dialysis patients, but to the group who have a manifest ROD with inconclusive turnover biomarkers. Extra efforts are needed to eliminate this old bone and brain toxin and to explore the disease burden in the rest of the CKD spectrum. Environmental studies and surveillance are needed to tackle and control the possible sources of aluminum exposure. Aluminum bone disease should be kept in our differential diagnosis list of renal osteodystrophy. Its diagnostic and therapeutic tools should be available widely, especially in developing countries that are not yet aluminum-free.