Building a network of ADPKD reference centres across Europe: the EuroCYST initiative

Clinical Characteristics and Kidney Outcomes in Chinese Patients with Autosomal Dominant Polycystic Kidney Disease

Key Points

The Mayo clinic imaging classification allows more accurate risk stratification but is limited by the lack of data on non-White populations and on atypical imaging patterns. In this cohort of Chinese patients with autosomal dominant polycystic kidney disease, an atypical imaging pattern was observed in 17% of the cases, associated with later presentation and a milder disease course. There may be genotypic differences, especially among those with atypical imaging. Future genotyping studies will help to define the genetic basis for the phenotypic spectrum in Chinese patients.

Background

The management of autosomal dominant polycystic kidney disease (ADPKD) remains challenging with variable and uncertain genotype–phenotype correlations. The Mayo clinic imaging classification allows more accurate risk stratification but is limited by the atypical imaging patterns. We aim to assess the clinical characteristics and the morphology of the cystic kidneys in a cohort of Chinese patients with ADPKD.

Methods

Ninety-eight patients with ADPKD were recruited prospectively from August 2019 to December 2020 in Prince of Wales Hospital, Hong Kong. They were subsequently followed up every 6 months for a minimum of 2 years. We reviewed the clinical characteristics and magnetic resonance imaging patterns at baseline and the kidney outcome at the end of the follow-up. Atypical imaging patterns included unilateral, segmental, asymmetric, lopsided, and bilateral atrophy as defined by the Mayo Imaging Classification.

Results

The mean age was 51.5±14.3 years, and the mean eGFR 68.7±27.5 ml/min per 1.73 m2. The 98 patients included 36 male and 62 female. Seventy-six patients (77.6%) had a family history. Seventeen of the 98 (17.3%) patients had atypical imaging patterns. Compared with typical cases, atypical cases were older at the time of diagnosis (49.5±16.0 versus 33.0±13.0 years, P < 0.001) and at the time of starting antihypertensive medications (52.4±14.8 versus 39.7±11.0 years, P = 0.001) and were less likely to have a positive family history (58.8% versus 81.5%, P = 0.042). Patients with atypical patterns showed a lower eGFR decline compared with those with the typical pattern (−0.86±4.34 versus −3.44±4.07 ml/min per 1.73 m2 per year, P = 0.022).

Conclusions

In this cohort of Chinese patients with ADPKD, an atypical imaging pattern was observed in 17% of the cases, associated with later presentation and a milder disease course. Future genotyping studies will help to define the genetic architecture and the basis for the phenotypic spectrum in Chinese patients with ADPKD.

Diffusion magnetic resonance imaging for kidney cyst volume quantification and non-cystic tissue characterisation in ADPKD

OBJECTIVES

Beyond total kidney and cyst volume (TCV), non-cystic tissue plays an important role in autosomal dominant polycystic kidney disease (ADPKD) progression. This study aims at presenting and preliminarily validating a diffusion MRI (DWI)-based TCV quantification method and providing evidence of DWI potential in characterising non-cystic tissue microstructure.

METHODS

T2-weighted MRI and DWI scans (b = 0, 15, 50, 100, 200, 350, 500, 700, 1000; 3 directions) were acquired from 35 ADPKD patients with CKD stage 1 to 3a and 15 healthy volunteers on a 1.5 T scanner. ADPKD classification was performed using the Mayo model. DWI scans were processed by mono- and segmented bi-exponential models. TCV was quantified on T2-weighted MRI by the reference semi-automatic method and automatically computed by thresholding the pure diffusivity (D) histogram. The agreement between reference and DWI-based TCV values and the differences in DWI-based parameters between healthy and ADPKD tissue components were assessed.

RESULTS

There was strong correlation between DWI-based and reference TCV (rho = 0.994, p < 0.001). Non-cystic ADPKD tissue had significantly higher D, and lower pseudo-diffusion and flowing fraction than healthy tissue (p < 0.001). Moreover, apparent diffusion coefficient and D values significantly differed by Mayo imaging class, both in the whole kidney (Wilcoxon p = 0.007 and p = 0.004) and non-cystic tissue (p = 0.024 and p = 0.007).

CONCLUSIONS

DWI shows potential in ADPKD to quantify TCV and characterise non-cystic kidney tissue microstructure, indicating the presence of microcysts and peritubular interstitial fibrosis. DWI could complement existing biomarkers for non-invasively staging, monitoring, and predicting ADPKD progression and evaluating the impact of novel therapies, possibly targeting damaged non-cystic tissue besides cyst expansion.

CLINICAL RELEVANCE STATEMENT

This study shows diffusion-weighted MRI (DWI) potential to quantify total cyst volume and characterise non-cystic kidney tissue microstructure in ADPKD. DWI could complement existing biomarkers for non-invasively staging, monitoring, and predicting ADPKD progression and evaluating the impact of novel therapies, possibly targeting damaged non-cystic tissue besides cyst expansion.

KEY POINTS

• Diffusion magnetic resonance imaging shows potential to quantify total cyst volume in ADPKD. • Diffusion magnetic resonance imaging might allow to non-invasively characterise non-cystic kidney tissue microstructure. • Diffusion magnetic resonance imaging-based biomarkers significantly differ by Mayo imaging class, suggesting their possible prognostic value.

Automated renal segmentation in healthy and chronic kidney disease subjects using a convolutional neural network

PURPOSE

Total kidney volume (TKV) is an important measure in renal disease detection and monitoring. We developed a fully automated method to segment the kidneys from T₂ -weighted MRI to calculate TKV of healthy control (HC) and chronic kidney disease (CKD) patients.

METHODS

This automated method uses machine learning, specifically a 2D convolutional neural network (CNN), to accurately segment the left and right kidneys from T₂ -weighted MRI data. The data set consisted of 30 HC subjects and 30 CKD patients. The model was trained on 50 manually defined HC and CKD kidney segmentations. The model was subsequently evaluated on 50 test data sets, comprising data from 5 HCs and 5 CKD patients each scanned 5 times in a scan session to enable comparison of the precision of the CNN and manual segmentation of kidneys.

RESULTS

The unseen test data processed by the 2D CNN had a mean Dice score of 0.93 ± 0.01. The difference between manual and automatically computed TKV was 1.2 ± 16.2 mL with a mean surface distance of 0.65 ± 0.21 mm. The variance in TKV measurements from repeat acquisitions on the same subject was significantly lower using the automated method compared to manual segmentation of the kidneys.

CONCLUSION

The 2D CNN method provides fully automated segmentation of the left and right kidney and calculation of TKV in <10 s on a standard office computer, allowing high data throughput and is a freely available executable.

Rationale and study protocol of ACQUIRE, a prospective, observational study measuring quality of life, treatment preference and treatment satisfaction of autosomal dominant polycystic kidney disease (ADPKD) patients in Europe

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is considered the most common inherited renal disease. Patient-Reported Outcomes (PROs) and patient experience in ADPKD are difficult to quantify and have not been well studied, particularly in the early stages of the disease. There is evidence to suggest that early-stage ADPKD patients have a lower Health-Related Quality of Life (HRQoL) than the general population due to the signs and symptoms of early-stage ADPKD. However, no research has been carried out on the HRQoL of early-stage ADPKD patients using validated ADPKD-specific PRO measures. Additionally, a new disease progression delaying treatment option has recently emerged for ADPKD. Patient preference for this treatment and unmet treatment needs have not yet been investigated.

METHODS

The ACQUIRE study is a prospective, observational study investigating the influence of early-stage ADPKD-related symptoms and treatments on PROs. It aims to collect real-world data on patient demographics, treatment patterns, clinical outcomes, and PROs such as HRQoL, treatment satisfaction and treatment preference in early-stage ADPKD. Adult ADPKD patients in stages 1-3 of chronic kidney disease (CKD) with evidence of rapidly progressing disease are being recruited from seven European countries. At baseline and every 3 months, for a follow-up period of 18 months, general and disease-specific questionnaires are completed remotely to capture patients' own assessment of their overall and ADPKD-related HRQoL. A Discrete Choice Experiment (DCE) is also used to investigate the value patients place on different attributes of hypothetical treatment options (e.g. treatment outcomes, side effects) and the role each attribute plays in determining overall patient treatment preference.

DISCUSSION

The results of this study will highlight the real-world effects of ADPKD-related challenges on PROs including HRQoL, treatment experience and satisfaction; and help physicians gain greater insight into likely disease outcomes based on early-stage patient symptoms and patients' experience with treatment. Data captured by the DCE may inform ADPKD treatment decision-making from a patient perspective. The DCE will also provide insights into which patients are more likely to perceive benefit from treatments based on the value and trade-offs they place on specific treatment attributes.

TRIAL REGISTRATION

NCT02848521 . Protocol Number/Version: 156-303-00096/Final.

Kidney volume measurement methods for clinical studies on autosomal dominant polycystic kidney disease

Background

In autosomal dominant polycystic kidney disease (ADPKD), total kidney volume (TKV) is regarded as an important biomarker of disease progression and different methods are available to assess kidney volume. The purpose of this study was to identify the most efficient kidney volume computation method to be used in clinical studies evaluating the effectiveness of treatments on ADPKD progression.

Methods and findings

We measured single kidney volume (SKV) on two series of MR and CT images from clinical studies on ADPKD (experimental dataset) by two independent operators (expert and beginner), twice, using all of the available methods: polyline manual tracing (reference method), free-hand manual tracing, semi-automatic tracing, Stereology, Mid-slice and Ellipsoid method. Additionally, the expert operator also measured the kidney length. We compared different methods for reproducibility, accuracy, precision, and time required. In addition, we performed a validation study to evaluate the sensitivity of these methods to detect the between-treatment group difference in TKV change over one year, using MR images from a previous clinical study. Reproducibility was higher on CT than MR for all methods, being highest for manual and semiautomatic contouring methods (planimetry). On MR, planimetry showed highest accuracy and precision, while on CT accuracy and precision of both planimetry and Stereology methods were comparable. Mid-slice and Ellipsoid method, as well as kidney length were fast but provided only a rough estimate of kidney volume. The results of the validation study indicated that planimetry and Stereology allow using an importantly lower number of patients to detect changes in kidney volume induced by drug treatment as compared to other methods.

Conclusions

Planimetry should be preferred over fast and simplified methods for accurately monitoring ADPKD progression and assessing drug treatment effects. Expert operators, especially on MR images, are required for performing reliable estimation of kidney volume. The use of efficient TKV quantification methods considerably reduces the number of patients to enrol in clinical investigations, making them more feasible and significant.

Clinical Manifestation and Management of ADPKD in Western Countries

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease in Western countries. The prevalence is between 2.4/10,000 and 3.9/10,000. ADPKD represents a systemic disease resulting in deterioration in renal function. Until now, mutations in two genes (PKD1 and PKD2) have been identified. Recently, the European Medicines Agency (EMA) approved the use of the vasopressin V2 receptor antagonist tolvaptan to slow the progression of cyst development and renal insufficiency connected with ADPKD in adult patients with chronic kidney disease stages 1-3 at initiation of treatment with evidence of rapidly progressing disease. Whereas the EMA approved the release of tolvaptan, the US Food and Drug Administration (FDA) requested further data on side effects and the selection of patient cohorts who may benefit from treatment.

SUMMARY

This review focused on advances in the management and treatment of ADPKD in Western countries.

KEY MESSAGE

ADPKD represents the fourth most common cause of end-stage renal disease (ESRD) in Western countries. ADPKD is a multisystemic disease characterized by the progressive development of bilateral renal cysts, resulting in enlargement of the kidney volume due to cystic formations, hypertension, hematuria, and loss of renal function. ADPKD is associated with high inter- and intrafamilial variability in disease appearance and progression. Patients with PKD1 mutations typically have a more severe phenotype than those with PKD2 mutations. ADPKD is under intensive investigation. Vasopressin and the associated cyclic adenosine monophosphate-related signaling pathways have been demonstrated to be important contributors to cyst growth in ADPKD. Supportive treatments are recommended with the aim of reducing morbidity and mortality associated with disease manifestations. In the past years, several agents have been investigated in ADPKD patients, including mTOR inhibitors, somatostatin analogs, statins, and vasopressin V2 receptor antagonists.

FACTS FROM EAST AND WEST

(1) ADPKD is diagnosed globally by ultrasound detection of kidney enlargement and presence of cysts. Recent analyses of variants of the PKD1 and PKD2 genes by next-generation sequencing in Chinese and Western ADPKD patients might lead to the development of reliable genetic tests. (2) Besides lifestyle changes (low-salt diet, sufficient fluid intake, and no smoking), blood pressure control is the primary nonspecific treatment recommended by Kidney Disease - Improving Global Outcomes (KDIGO) for ADPKD patients. How low the blood pressure target should be and what the means of achieving it are remain open questions depending on the severity of chronic kidney disease and the age of the patients. In a recent Chinese study, diagnostic needle aspiration and laparoscopic unroofing surgery successfully improved infection, pain, and hypertension. Peritoneal dialysis was found to be a feasible treatment for most Chinese ADPKD patients with ESRD. In most Western centers, patients without contraindication are selected for peritoneal dialysis. Kidney transplantation with concurrent bilateral nephrectomy was successful in relieving hypertension and infection in Chinese ADPKD patients. In Western countries, sequential surgical intervention with kidney transplantation after nephrectomy, or the other way round, is preferred in order to reduce risks. (3) The vasopressin 2 receptor antagonist tolvaptan was approved in Europe, Canada, Japan, and Korea to slow down progression of kidney disease in ADPKD patients. Tolvaptan is not yet approved in the USA or in China. mTOR pathway-targeting drugs are currently under evaluation: mTOR inhibitors could slow down the increase in total kidney volume in a cohort of Western and Japanese ADPKD patients. Western studies as well as an ongoing study in China failed to show benefit from rapamycin. A study performed in Italy indicates protective effects of the somatostatin analog octreotide in ADPKD patients. Western and Chinese studies revealed a potential beneficial effect of triptolide, the active substance of the traditional Chinese medicine Tripterygium wilfordii (Lei Gong Teng) to prevent worsening in ADPKD patients.

Autosomal Dominant Polycystic Kidney Disease: A Path Forward

Autosomal dominant polycystic kidney disease (ADPKD) is the commonest inherited cause of renal failure in adults, and is due to loss-of-function mutations in either the PKD1 or PKD2 genes, which encode polycystin-1 and polycystin-2, respectively. These proteins have an essential role in maintaining the geometric structure of the distal collecting duct in the kidney in adult life, and their dysfunction predisposes to renal cyst formation. The typical renal phenotype of ADPKD is the insidious development of hundreds of renal cysts, which form in childhood and grow progressively through life, causing end-stage kidney failure in the fifth decade in about half affected by the mutation. Over the past 2 decades, major advances in genetics and disease pathogenesis have led to well-conducted randomized controlled trials, and observational studies that have resulted in an accumulation of evidence-based data, and raise hope that the lifetime risk of kidney failure due to ADPKD will be progressively curtailed during this century. This review will provide a contemporary summary of the current state of the field in disease pathogenesis and therapeutics, and also briefly highlights the importance of clinical practice guidelines, patient perspectives, patient-reported outcomes, uniform trial reporting, and health-economics in ADPKD.

Risk factors for progression in ADPKD

PURPOSE OF REVIEW

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease. This article will describe the factors associated with both functional and structural evidence of disease progression. It will also review the results of recent clinical trials that have shown an impact on markers of disease progression.

RECENT FINDINGS

A variety of prognostic factors have been described that relate to a decline in glomerular filtration rate or an increase in total cyst or kidney volumes. We now have clinical trials that show that glomerular filtration rate decline and kidney volume growth can be slowed in those with ADPKD.

SUMMARY

With the emergence of potential disease-modifying therapies, factors that can accurately identify those who are most at risk for renal progression or ADPKD-related complications need to be identified and validated.

The Treatment of Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

About one in 2000 persons in Europe suffers from autosomal dominant polycystic kidney disease (ADPKD). The treatment of this disease up to the present has been limited to the management of complications.

METHODS

This review is based on pertinent publications, mostly of the last three years, that were retrieved by a selective search in PubMed.

RESULTS

Kidney volume is probably the most important predictive factor for the loss of renal function. A measurement of kidney size is, therefore, recommended as soon as the diagnosis is made. ADPKD patients under age 30 with a combined kidney volume above 1500 mL and an estimated glomerular filtration rate (eGFR) below 90 mL/min are at high risk of needing kidney-replacement therapy (dialysis or transplantation) within 20 years, even if their renal function is normal. Ultrasonographic follow-up can identify affected persons whose risk for rapid progression is especially high. Currently available evidence reveals that, in patients at risk whose renal function is normal, the maintenance of blood pressure at or below a target value of 110/75 mmHg lessens renal enlargement, albuminuria, and left-ventricular hypertrophy. In another study, the treatment of selected patients with tolvaptan, a vasopressin-2 receptor (V2R) blocker, was found to delay cyst enlargement and the related decline in renal function for three years. It is unclear, however, how long the effect of tolvaptan persists, or whether persons whose renal function is already impaired can benefit from it. The main side effects are marked polyuria and, in rare cases, liver toxicity.

CONCLUSION

In patients with ADPKD, an effort should be made to keep the arterial blood pressure below 120/80 mmHg. In patients at high risk of progression whose renal function is still intact (eGFR > 60 mL/min), strict blood pressure control (< 110/75 mm Hg) is indicated, and possibly V2R blockade with tolvaptan as well. Tolvaptan is an expensive drug, and patients taking it must be carefully monitored for hepatotoxicity.

Autosomal dominant polycystic kidney disease: the changing face of clinical management

Autosomal dominant polycystic kidney disease is the most common inherited kidney disease and accounts for 7-10% of all patients on renal replacement therapy worldwide. Although first reported 500 years ago, this disorder is still regarded as untreatable and its pathogenesis is poorly understood despite much study. During the past 40 years, however, remarkable advances have transformed our understanding of how the disease develops and have led to rapid changes in diagnosis, prognosis, and treatment, especially during the past decade. This Review will summarise the key findings, highlight recent developments, and look ahead to the changes in clinical practice that will likely arise from the adoption of a new management framework for this major kidney disease.