There have been many reports of a spectrum of biopsy-proven renal disease in the plain region; however, due to limited renal biopsy technology, the spectrum of renal disease in the plateau region is unclear. Since medical groups aided Tibet in 2015, with the help of experienced nephrologists from Peking University First Hospital, the local hospital has successfully carried out more kidney biopsies. This study was conducted to understand the spectrum of renal disease in the Tibetan region in recent years. It is the largest study conducted on biopsy-proven renal disease patients at high altitude to date.
In our study, PGN was the most common renal disease at high altitude in Tibet, affecting 63.2% of patients, which was slightly lower than the range of 65.1-81.55% reported by other centers in other geographic regions of China [6–14]. MN was the most common PGN, followed by IgAN. In addition, we observed a tendency toward male predominance in the total MN population, and the sex difference was significant, which was different from a previous study [9]. Zhou et al. [15] analyzed 107 patients from June 2010 to October 2013 in Tibet, and the results showed that the most frequent type of PGN was podocyte diseases which were pathological ambiguous descriptions. Most Chinese single-center studies showed that IgAN was still the most common PGN [7, 8, 13, 14, 16], although the proportion of MN was significantly increased [6–14, 17], and even MN has overtaken IgAN as the most common PGN in some areas, such as Central [11] and Northeast [9] China. Our findings in this study in Tibet also confirmed this trend. However, because few people underwent renal biopsy for isolated asymptomatic hematuria and/or proteinuria, the incidence of IgAN in Tibet might be underestimated. In addition, MCD accounted for 15.5% of PGN in our study, exceeding the range seen in other areas of China (8.1–14.81%) [8, 9, 14, 16, 17].
Previous studies showed that among plateau residents, female patients were more vulnerable to renal diseases than males [15, 18]. Although the female patients are younger (38.9 ± 15.1 versus 42.1 ± 15.7 y, P = 0.035) in our cohort, consistent with the results of most previous large studies in other regions of China [6, 8–13], the overall sex distribution in our study was also male predominant (60%, 259/429).
The majority of the patients were young and middle-aged, with 68.8% in the 25-59-year-old group, interestingly, this is equivalent to a multicenter study from northeast China [13]. Due to the improvement in economic conditions, enhancement of health consciousness and advancements in the technology and safety of renal biopsy, the number of patients over 60 years old undergoing renal biopsy has increased dramatically [8, 10, 13, 19]. In our study, the proportion of ≥ 60-year-old (elderly) patients was 14.0%. Another study in the Tibetan Plateau showed that only 6.5% of renal biopsy patients were over 50 years old [15]. The relatively high number of elderly patients in the last few years may be related to the aging of the Chinese population, as well as the rapid development of hygiene and health undertakings in Tibet, such as health poverty alleviation, basic sanitation facilities and health aid to Tibet. MN is the most common PGN among elderly individuals in Tibet, which is consistent with previous studies [7, 8, 19–22].
Approximately half of the patients presented with NS. Approximately 70% (74/107) of patients in another study on Tibetan inhabitants also presented with nephrotic syndrome. NS was the most common indication for biopsy in the plateau region, which was roughly the same as previous studies [6, 8, 9, 11]. Considering the limited resources and relatively underdeveloped economy in the Tibetan Plateau region, Tibetan residences are scattered and remote, and their awareness of routine medical examination is relatively weak. They visit the hospital for diagnosis and treatment only when they have edema, gross hematuria, hypertension and other common symptoms of kidney disease. This might be one of the reasons why NS was the most common clinical presentation.
In our study, DN was the most common SGN among Tibetan inhabitants, in contrast to IgAVN, as reported by Zhou et al. [15, 18] in 2014. The main reasons for DN becoming the most common SGN included the following: (1) the prevalence of DM in China is significantly increasing [23, 24], and the threshold for renal biopsy for DN is decreasing, and (2) the People’s Hospital of Tibet Autonomous Region, as the largest hospital in Tibet, accepts the referral population from other local hospitals where renal biopsy cannot be performed. Another interesting phenomenon was the low prevalence of LN among Tibetan inhabitants, only accounting for 12.7% (16/126) of SGN, which is much lower than that in plain areas of China (29.2%-34.3%)[11, 13, 14]. In view of the real incidence and prevalence of SLE in high altitude region such as Nepal, Tibet China is largely not known [25, 26], we couldn’t explain why LN was less common in plain areas so far. Widespread hepatitis B virus (HBV) vaccinations in China since 1992 have led to a marked reduction in HBV infections, and only one adult has been definitely diagnosed with HBV-GN [27]. MCD and CMSAN were more common among secondary polycythemia patients than in nonpolycythemia patients and heavier proteinuria[5]. The possible cause was that glomerular podocytes are more sensitive to hypoxic stimulation [28]. Therefore, the high hemoglobin group should be followed with special attention to proteinuria, which may accelerate renal function progression.
There were several limitations of our study. First, as an observational study, we successfully described the spectrum of renal disease in this region but cannot explain its underlying causes. Second, the People’s Hospital of Tibet Autonomous Region, as a tertiary referral hospital in the Tibet Autonomous Region, received many referral patients, particularly severely ill patients. Selection bias is inevitable. Third, we do not have long-term follow-up data. Finally, although the cases at the People's Hospital of Tibet Autonomous Region, as the largest hospital in Tibet, are somewhat representative of the spectrum of renal diseases in high-altitude regions, the study was still a single-center study.