Older adults with kidney disease—epidemiology and clinicopathologic correlations: a remarkable single-center survey

The occupants of our globe, on average, are steadily growing older consequent to lower birth rates and longer life expectancy. While the actual tempo of this global aging process varies from region to region, due to the impact of epidemics of disease (e.g. AIDS), reduced infant mortality, hygiene, malnutrition and violence, there is little doubt that the aging of society as a whole will have profound effects on healthcare systems and clinical practice. The discipline of nephrology is not exempt from these events, indeed it has already been and is continuing to be impacted by the aging of society, particularly in income-rich countries. The prevalence of acute and chronic kidney diseases is expected to increase significantly in the next few decades, largely in the older adult population. The specific causes or nature of these diseases are quite heterogeneous and often difficult to categorize on clinical grounds alone. Renal biopsy has been and continues to be a powerful tool to add precision to diagnosis. Many surveys of renal pathology, as it exists in a given population and how it changes over time, have been published, mostly collected in regional renal biopsy registries, but relatively few have focused mainly on the older and elder adult, conventionally defined as having attained the age of 65 years or more [1–3]. The survey by Jin et al. [4] from Jinling Hospital and the Nanjing University School of Medicine in Nanjing, China, published in this issue of Nephrology Dialysis Transplantation is a good example of this kind of morphological/epidemiological investigation. Remarkably, over 29 000 renal biopsies were performed in adults (age 18–81 years) at a single center over a 10-year period, of which ∼850 (2.9%) were performed in older or elder adults. These older subjects had a variety of clinical presentations and indications for performance of renal biopsy, but the actual rate of renal biopsy performance is not precisely known, but a rate of ∼2900 renal biopsies per year would be high by any standard. Undoubtedly, selection pressures such as the referral nature of and the cachement areas sub-served by the center play large roles in the epidemiological observations reported. Not surprisingly, proteinuria (including nephrotic syndrome; NS) with or without hematuria or acute kidney injury (AKI) was commonly the reason for performance of renal biopsy—observed in almost two-thirds of the subjects. Glomerular or vasculitic diseases predominated— slightly over 70% of all biopsies showed lesion of membranous nephropathy (MN), IgA nephropathy (IgA N), minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), small vessel vasculitis (SVV), diabetic nephropathy (DN) or amyloidosis (AM). DN is likely under-represented (at 9.75%) in this series, compared with its actual prevalence in the population as a whole—even though in this series renal biopsies were performed in diabetic subjects with renal involvement and without biopsy ‘contraindications’. It is not clear if the extent of ‘atypical’ characteristics at presentation influenced the decision to perform renal biopsy in diabetic subjects. Among elderly subjects presenting with NS, four lesions (MN, AM, MCD and IgA N) accounted for 80% of those observed. The distribution of these lesions in the elderly is strikingly different from that observed in the ‘control’ younger population. It is also noteworthy that the most common lesion in the very old (>75 years) was MN. Of great interest is the low prevalence of lesions of FSGS in both the young and old subjects alike (5.8 and 4.7%, respectively). Among older patients presenting with NS (with or without AKI) on only 28/851 (3.3%) demonstrated FSGS on renal biopsy. The frequency of FSGS in this and other studies in Asians is much different that seen in non-Asian populations, especially in subjects of African ancestry [5]. This difference is likely explained on a genetic basis (lack of APOL1 risk alleles in Asians), but environmental influences cannot be excluded [6]. The relative rarity of ‘primary’ or ‘idiopathic’membrano-proliferative glomerulonephritis (MPGN) in the elderly is notable (only 7 in 851 cases; 0.82%). These data support the contemporary view that IN F O C U S