Changes in renal function and morphological variations of kidney diseases in rheumatoid arthritis patients

Abstract

Objective

Rheumatoid nephropathy is one of the most severe extra-articular manifestations of rheumatoid arthritis (RA) associated with a very unfavorable prognosis. This study aimed to identify changes in renal function and morphological variations of kidney diseases in RA patients.

Methods

The study enrolled patients (126 patients) between 18 and 55 years of age with a confirmed active RA of more than 12 months. Each patient underwent the following range of laboratory and instrumental research methods: general clinical analysis of blood and urine, performing urinalysis according to Nechiporenko method; determining daily proteinuria; determining the blood content of glucose, urea, creatinine, uric acid, total bilirubin, liver transaminase level, ionogram, lipidogram, and coagulogram; determining the blood content of rheumatoid factor, anti-streptolysin O, and C-reactive protein; and X-ray of the joints of hands and feet. Renal function was examined by estimating glomerular filtration rate, tubular reabsorption index, and renal functional reserve. For studying the morphological changes in the kidneys under ultrasound examination, renal biopsy was performed in 31 patients with RA with urinary syndrome (proteinuria more than 0.3 g per day and hematuria).

Results

Nephropathy in RA is characterized by impaired renal function and manifested by an increased blood creatinine and a decrease in glomerular filtration rate and renal functional reserve. Among morphological variations of nephropathy at RA, mesangial proliferative glomerulonephritis prevails, accounting for 48.4% of patients. Other disorders include the secondary amyloidosis (29.0% of patients), tubulointerstitial nephritis (16.1%), membranous glomerulonephritis (3.2%), and focal-segmental glomerulosclerosis (3.2%).

Conclusion

Kidney damage is a common systemic manifestation of RA with a long and active course, a major nephropathy trigger.

1. Introduction

Rheumatoid arthritis (RA) is the most frequent autoimmune disorder and one of the leading connective tissue and musculoskeletal system diseases [[1], [2], [3]]. Epidemiological data indicate that nearly 20 million people in 195 countries have RA. Specifically, the incidence of RA in the United Kingdom was 472 cases per 100 000 inhabitants [4]. It should be noted that the incidence of this nosology in females is 2–4 times greater than in males [[5], [6], [7]]. RA has equally high medical and social significance. Thus, the RA has a 54% higher mortality rate than the overall population. This fact is of particular concern in modern medical science [[8], [9], [10]].

RA is a systemic autoimmune disease that continuously raises many questions about etiopathogenesis [11,12]. According to scientists, key etiopathogenetic factors of RA are genetics, endogenous (citrulline proteins and peptides), and infectious agents (universal stress proteins A, retroviruses, Epstein-Barr virus, and parvovirus B19), as well as smoking [12,13]. The major pathophysiological mechanism for RA is believed to be systemic autoimmune inflammation, with a primary target being the synovial membrane of the joints [[14], [15], [16], [17]].

Generally, RA is characterized by the progressive course and generalized nature of the disease, involving the joints and numerous other organs and organ systems, adversely affecting the prognosis of the disease [18,19]. Among the extra-articular manifestations of RA, one of the most serious is kidney damage, known as rheumatoid nephropathy, diagnosed in 57%–73% of patients with RA [[20], [21], [22]]. Kidney damage in RA is characterized by a progressive course with a decrease in the number of functionally active nephrons and the progression of nephrosclerosis. Eventually, it leads to a relatively rapid chronic kidney disease, with the prognosis for a patient being extremely unfavorable [[22], [23], [24]]. Despite advances in modern rheumatology and medical science in general, questions remain about the mechanisms of kidney damage in RA, its progression, early and timely diagnosis of rheumatoid nephropathies, and treatment tactics [25,26]. Research in this regard is therefore urgently required.

The study purpose was to determine changes in renal function and morphological variations of their lesions in patients with RA.

2. Patients and methods

The study enrolled 126 patients between 18 years and 55 years of age with a confirmed active RA of more than 12 months. The protocol of the study and the form of written consent of a patient to participate in the study were considered in detail and approved at the meeting of the Ethics Commission of Federal State-Funded Educational Institution of Higher Education at Irkutsk State Medical University (No. 14/a-1 of January 20, 2015). Only those who gave their voluntary and informed consents to participate in the study were included. This study was carried out between March 2015 and December 2020.

Exclusion criteria were Felty’s syndrome, Still’s disease, nephropathy of another genesis, urological or nephrological pathology, other rheumatologic diseases, acute somatic or surgical pathology, other chronic diseases at acute, subcompensation or decompensation stage, oncological pathology of any localization, mental pathology, infections, pregnancy or lactation, or unwillingness of a patient to participate in the study.

RA was diagnosed according to 2010 recommendations of the American College of Rheumatology and European League Against Rheumatism [26], and 2016 recommendations of the European League Against Rheumatism for the management of early arthritis [18]. The extent of RA activity was determined using the Disease Activity Score 28 (DAS28) index estimated using an online DAS calculator at http://www.das-score.nl/das28/en. The DAS28 index values of up to 2.5 points were considered as the remission of RA, 2.6–3.2 points considered as RA with low activity, 3.3–5.1 points considered as RA with moderate activity, 5.2 and more points considered as RA with high activity.

Depending on the patients’ ability to work and the presence or absence of a disability, four functional classes (FCs) of RA were distinguished: FC I means no restrictions on functional activity; FC II means restriction of professional activity; FC III means restriction of non-professional activity; FC IV means disability [18,26].

To determine the radiological stage of RA, standard radiography of patients' feet and hands was performed. Radiological stages of the disease were determined based on Steinbrocker criteria [19].

Laboratory tests included general clinical analysis of blood and urine, performing urinalysis according to Nechiporenko method [27]; determining daily proteinuria (PU); determining the blood content of glucose, urea, creatinine, uric acid, total bilirubin, liver transaminase level, ionogram, lipidogram, and coagulogram; determining the blood content of rheumatoid factor, anti-streptolysin O, and C-reactive protein.

To determine daily PU, urine was collected for 24 h in a 3 L plastic container, and the container together with the collected urine was stored in the refrigerator. Urine collection for daily PU was performed during a patient's usual diet and drinking. The first morning portion of urine was poured out, and the time of the beginning of urine collection was fixed. The last portion of urine was collected at the same time as the first portion of urine (spilled portion). Subsequently, the volume of urine taken during the day was measured, after which the urine was mixed, and 100 mL was taken to determine the daily PU on the Siemens Advia 1800 analyzer (Siemens Healthcare Diagnostics, Erlangen, Germany). The level of PU was assessed in gram per day: less than 0.5 g per day (slight PU), 0.5–3.0 g per day (moderate PU), and more than 3.0 g per day (severe PU).

In the absence of PU in daily urine analysis, semi-quantitative determination of albumin content (for microalbuminuria [MAU] screening) was performed using MicroalbuPHAN (Erba Lachema, Brno, the Czech Republic) diagnostic strips. MAU was defined as daily urinary albumin excretion of 0.02–0.30 g per day.

All patients underwent X-ray of the joints of hands and feet on General Medical Merate S.p.A Calypso F apparatus (Via Partigiani, Seriate BG, Italy), ultrasound diagnostics of the abdominal cavity, kidneys, and small pelvis organs on Combison 530 apparatus (Kretztechnik, Zipf, Austria), and electrocardiography on SE-601 device (Edan Instruments, Shenzhen, China).

Renal function was examined by estimating glomerular filtration rate (GFR), tubular reabsorption index, renal functional reserve (RFR), as well as based on blood urea and creatinine content analysis.

GFR was calculated by the Cockcroft-Gault formula using a calculator (https://www.mdcalc.com/creatinine-clearance-cockcroft-gault-equation). Tubular reabsorption was determined according to the formula:

$$\text{Tubular reabsorption }=\frac{\left(\text{GFR }-V_{\text{min}}\right)}{\text{GFR}}\text{ × }100\text{\%}$$

where V_min is the minute diuresis.

The RFR was studied according to the Bosch et al.’s method [28].

For studying the morphological changes in the kidneys under ultrasound examination, renal biopsy was performed (according to Kark and Muehrcke [29]) in 31 patients with RA with urinary syndrome (PU more than 0.3 g per day and hematuria). Renal biopsy was performed in the absence of contraindications to its implementation and in the presence of a patient's signed informed consent to perform this procedure. During histological analysis of specimens under light microscopy, activity index (AI) and sclerosis index (SI) were evaluated semi-quantitatively. AI was defined as the sum of the following pathomorphological nephritis signs: the proliferation of mesangial cells and podocytes, intracapillary infiltration, neutrophil infiltration, presence of demilunes, deposits, karyorrhexis, vasculitis, interstitial inflammation, and platelets in glomeruli. The SI was assessed by the presence of the following morphological criteria: the degree of hyalinosis and sclerosis of the glomeruli, the presence of crumpled glomerulus, synechias, periglomerular sclerosis and/or hyalinosis, diffuse or focal stromal sclerosis, sclerosis of the mesangial matrix, and atrophy of tubules. The intensity of each morphological sign was estimated from 0 to 3 points (0 point: no signs; 1 point: minimal changes; 2 points: moderate changes; 3 points: maximum expressed changes). The number of points was summed up, and the maximum number of points for AI and SI was 24 points (a total of 8 signs with 3 points each).

Statistical data processing was performed using Statistica for Windows 10 Pro (StatSoft inc., Tulsa, OK, USA) and Microsoft Excel 2013 (Microsoft Corporation, Redmond, Washington, USA) software. Mann-Whitney U-criterion was applied to compare quantitative parameters. Qualitative parameters were compared by calculating the odds ratio (OR) using Past 4.03 for Windows (Paleontological Statistics Software Package for Education And Data Analysis, Oyvind Hammer, Oslo, Norway). At p<0.05, the differences were considered statistically significant. Correlation analysis was performed according to Spearman's method.

3. Results

The study involved 126 patients with active RA, of whom 92 (73.0%) were women, and 34 (27.0%) were men. The age of the patients varied between 26 years and 55 years (mean±standard deviation [SD] 43.18±6.84 years). The length of the RA ranged from 2 years to 18 years (mean±SD 10.25±4.78 years). Of the patients studied, 36 (28.6%) had RA without kidney damage, and 90 (71.4%) patients were diagnosed with RA and kidney disease. The control group consisted of 30 apparently healthy persons (AHPs). Of them, 20 (66.7%) were women, and 10 (33.3%) were men, with mean age and SD of 43.55±5.49 years.

The study of the RA course showed the mean disease AI (DAS28 index) and SD of 5.28±0.36. Moreover, high activity of RA was observed in 77 (61.1%) patients, moderate activity in 42 (33.3%), and low activity in 7 (5.6%). In patients with RA without kidney damage, high activity was in 17 (47.2%) patients; in patients with RA with kidney damage, high activity was in 60 (66.7%) patients (OR 2.24, 95% confidence interval [CI] [1.02–4.91], p<0.05); the moderate activity was in 14 (38.9%) patients with RA without kidney damage and in 28 (31.1%) patients with RA with kidney damage (OR 1.40, 95% CI [0.63–3.15], p>0.05); low activity of the process was in 5 (13.9%) patients with RA without kidney damage and in 2 (2.2%) patients with RA with kidney damage (OR 7.10, 95% CI [1.31–38.47], p<0.05). Among patients with RA without renal impairment, the advanced stage of RA was in 23 (63.9%) patients; the renal impairment was in 39 (43.3%) patients (OR 2.31, 95% CI [1.04–5.14], p<0.05), and late stage in 13 (36.1%) patients with RA without kidney damage and in 51 (56.7%) patients with RA with kidney damage (OR 2.51, 95% CI [1.11–5.65], p<0.05).

The first radiological RA stage was observed in 2 (5.6%) patients without renal dysfunctions and was not detected among patients with kidney damage. The second radiological stage was stated in 18 (50.0%) patients with RA without kidney damage and in 40 (44.4%) patients with RA with kidney damage (OR 1.25, 95% CI [0.58–2.71], p>0.05). The third stage was in 15 (41.7%) patients with RA without kidney damage and 41 (45.6%) patients with RA with kidney damage (OR 1.17, 95% CI [0.54–2.56], p>0.05). The fourth stage was in 1 (2.8%) patient with RA without renal impairment and in 9 (10.0%) patients with RA with renal impairment (OR 3.89, 95% CI [0.47–31.88], p>0.05).

The distribution by FC was as follows: FC I was recorded in 8 (22.2%) patients with RA without kidney damage and in 9 (10.0%) patients with RA and kidney damage (OR 2.89, 95% CI [1.02–8.19], p<0.05); FC II was observed in 27 (75.0%) patients with RA without renal impairment and 76 (84.4%) patients with RA with renal impairment (OR 1.06, 95% CI [0.44–2.55], p>0.05), respectively; FC III was recorded in 1 (2.8%) patient with RA without renal impairment and 5 (5.6%) patients with RA with renal impairment (OR 2.06, 95% CI [0.23–18.27], p>0.05).

The study of renal functional activity showed that RA was characterized by diminished indices. Thus, in patients with RA and nephropathy with MAU, mean blood creatinine increased 1.20 times compared to AHPs (p<0.05). This indicator was 1.44 times higher (p<0.05) in patients with RA and nephropathy with PU, and a statistically significant difference was between patients with MAU and PU (p<0.05). There were no statistically significant differences in blood urea levels across the comparison groups (p>0.05) (Table 1).

Table 1.

Indicators of renal function in patients with active RA^a.

Indicator	AHPs (n=30)	Patients with RA and nephropathy		RA patients without kidney damage (n=36)
		With MAU (n=46)	With PU (n=44)
Creatinine, μmol/L	66.28±3.15	79.83±3.46b	95.29±4.03b,c,d	69.13±2.81
Urea, mmol/L	4.39±0.42	5.67±0.51	4.65±0.46	4.41±0.40
Leukocytes in 1 mL urinee	460.30±40.6	509.70±52.80	1137.40±73.20b,c,d	482.50±47.30
Erythrocytes in 1 mL of urinee	246.50±29.7	261.30±40.60	995.40±51.69b,c,d	275.10±32.80
RFR, mL/min	108.47±2.51	99.62±2.74	87.19±3.11b,c,d	106.15±1.99
Daily PU, g/day	0.02±0.001	0.15±0.003b,c	0.52±0.01b,c,d	0.03±0.001
MAU, g/L	0.008±0.001	0.024±0.002b,c	NAf	0.01±0.001
TR, %	99.07±0.1	99.02±0.16	98.97±0.14	99.06±0.13
RFR, %	19.10±0.53	13.31±0.45b,c	5.38±1.37b,c,d	18.27±0.62

RA, rheumatoid arthritis; AHPs, apparently healthy persons; MAU, microalbuminuria; PU, proteinuria; TR, tubular reabsorption; RFR, renal functional reserve; NA, not applicable.

^aValues are presented as mean±standard deviation.

^bDifferences are statistically significant compared to AHP (p<0.05).

^cDifferences are statistically significant compared to the index in patients with RA without kidney damage (p<0.05).

^dDifferences are statistically significant compared to the index in RA patients with kidney damage and MAU (p<0.05).

^eDetected per Nechiporenko method.

^fNA in this group because of the PU in these patients.

Also, in patients with RA and nephropathy with PU, an absolute mean leukocyte count in urine, according to Nechiporenko, increased 2.47 times (p<0.05) and mean erythrocyte count 4.04 times (p<0.05) compared to AHPs. However, there was a statistically significant difference when comparing these figures to patients with MAU (p<0.05) and RA without kidney damage (p<0.05). In RA patients with MAU, there was only a tendency to an increase in urine leukocyte (p>0.05) and erythrocyte count (p>0.05) compared to AHPs.

In RA patients with PU, kidney damage was accompanied by a 1.24-fold (p<0.05) decrease in RFR compared to AHPs. In patients with MAU, there was only a tendency to a GFR decrease (p>0.05).

Kidney damage in RA patients was accompanied by a significant (p<0.05) increase in protein content in daily urine compared to AHPs (Table 1).

When analyzing tubular reabsorption in patients with RA and kidney damage, no significant differences (p>0.05) were found compared to AHPs or patients with RA but without kidney damage. However, a decrease in RFR was typical of renal damage in RA. Thus, at RA with kidney damage and MAU, this index was 1.44 times lower compared to AHPs (p<0.05) and 1.37 times lower compared to RA patients without nephropathy (p<0.05). At RA with kidney damage and PU, the RFR was 3.55 times (p<0.05) lower compared to AHPs, 3.40 times (p<0.05) lower compared to RA patients without nephropathy, and 2.47 times (p<0.05) lower compared to RA patients with kidney damage and MAU.

When analyzing similar indices of renal function in patients with RA without nephropathy, no statistically significant differences were found in this group compared to AHPs (p>0.05).

The study on morphological peculiarities of kidney damage in 31 RA patients revealed that the most frequent disorder was mesangial proliferative glomerulonephritis (15 [48.4%] patients) manifested by focal or segmental enlargement of a mesangial matrix. secondary amyloidosis was detected in 9 (29.0%) patients with RA. Five (16.1%) patients were diagnosed with tubulointerstitial nephritis, which was characterized in these patients by atrophy and dystrophy of the epithelium of distal and proximal convoluted tubules, sclerotic changes, and lymphoid infiltration. The membranous glomerulonephritis was recorded in 1 (3.2%) patient, as well as focal-segmental glomerulosclerosis also in 1 (3.2%) patient (Fig. 1).

Figure 1.

Morphological variations of kidney damage in rheumatoid arthritis patients (n=31). TIN, tubulointerstitial nephritis; SA, secondary amyloidosis; MGN, membranous glomerulonephritis; MPGN, mesangial proliferative glomerulonephritis; FSGS, focal segmental glomerulosclerosis.

The study of AI during the inflammatory process in the kidneys and the morphological study of renal biopsy specimens showed the mean specified index and SD amounted to 4.07±0.18 points. The mean integral SI was 5.12 points with SD of 0.14 points. Correlations between morphological AI of the inflammatory process in the kidneys and DAS28 index (r=0.63, p<0.05), SI and DAS28 index (r=0.41, p<0.05), SI and duration of RA (r=0.50, p<0.05) were established.

4. Discussion

This study focused on the specifics of renal morphofunctional status in patients with RA. Based on the data obtained in the study, kidney damage in RA is a widespread phenomenon. Thus, out of 126 RA patients included in the study, kidney damage was diagnosed in 90 (71.4%) patients. The main sign indicating its presence was MAU and PU, which significantly exceeded (p<0.05) similar indices in AHPs and the group of RA patients without kidney damage. MAU is the most important marker of renal dysfunction used as a mandatory screening method to detect nephropathy in various diseases. The cause of MAU in patients under study is an increase in GFR displayed by RFR. It was also confirmed by the fact that in RA patients with nephropathy, RFR was significantly lower (p<0.05) compared to AHPs (Table 1). A pronounced urinary syndrome was typical for kidney damage in RA patients manifested not only by PU but also by significant leukocyte level and hematuria. It should be noted that all of these changes were most pronounced within the PU patient group. Statistically significant decrease of RFR (p<0.05) and increase of creatinine blood content (p<0.05) as an indicator of impaired renal nitrogen-excretory function also testified to more unfavorable kidney damage in RA patients with PU. Furthermore, rheumatoid nephropathy in the studied patients was not accompanied by visible edema, arterial hypertension, anuria, or macrohematuria. That means that nephropathy had a latent course. It is also important that the severity of nephropathy was higher in patients with a more active and longer course of RA. It is confirmed by the correlations between the DAS28 index and daily PU (r=0.64, p<0.05), MAU (r=0.50, p<0.05), blood creatinine (r=0.31, p<0.05), GFR (r=−0.26, p<0.05); duration of RA and daily PU (r=0.33, p<0.05), MAU (r=0.30, p<0.05); daily PU and blood creatinine content (r=0.32, p<0.05); severity of nephropathy and DAS28 index (r=0.33, p<0.05), duration of RA (r=0.35, p<0.05).

Therefore, it can be assumed that one of the important nephropathy triggers during RA is its long and highly active course.

Morphological study results of renal biopsy specimens in RA patients allow stating that nephropathy in RA is characterized by involvement of tubulointerstitial renal structures and glomerular mechanisms with a prevalence of mesangial proliferative variation of kidney damage (mesangial proliferative glomerulonephritis) with pronounced urinary syndrome. The progression of secondary renal amyloidosis was rather common in RA patients, which was revealed in 9 (29.0%) persons out of 31 by the morphological study of renal biopsy specimens. Noteworthy, the presence of secondary amyloidosis in RA patients was associated with a long history of RA (more than 9 years), high disease activity, a greater degree of PU, and more pronounced functional disorders of the joints. The study results of the morphological condition of kidneys at RA testify that RA significantly facilitates the progression of nephropathy. In contrast, duration and disease activity initiate the formation of sclerosis and amyloidosis of kidneys at RA. That is also proved by established correlations between AI of an inflammatory process in kidneys and DAS28 index (r=0.63, p<0.05), SI and DAS28 index (r=0.41, p<0.05), and SI and duration of RA (r=0.50, p<0.05).

The results of the study on the morphofunctional condition of kidneys at RA, in general, are in line with the results of other research conducted in this direction. Thus, the study by Vinicki et al. [30] on clinical and morphological peculiarities of kidney damage in 65 RA patients established that the most frequent clinical manifestations of kidney damage in RA were nephrotic syndrome (in 60.0% of patients) and hematuria (in 46.0% of patients) with or without PU. The morphological pattern of rheumatoid nephropathy was as follows. Renal amyloidosis was verified in 20 (31.0%) patients, mesangial proliferative glomerulonephritis in 12 (18.0%) patients, membranous nephropathy in 11 (17.0%) patients, extra capillary proliferative glomerulonephritis in 10 (15.0%) patients, focal-segmental glomerulosclerosis in 6 (9.0%) patients, nephropathy with minimal changes in 3 (5.0%) patients, and tubulointerstitial nephritis in 3 (5.0%) patients [30].

According to the study by Mori et al. [20] that included 1908 RA patients, the prevalence of renal dysfunction manifested by decreased GFR among studied patients was 33.8%; albuminuria was recorded in 8.1% of patients, hematuria in 7.5% of patients, and the risk factors of kidney damage progression included old age (OR=7.24, p<0.001), obesity (OR=0.59, p<0.001), hypertension (OR=2.22, p<0.001), and female gender (OR=3.12, p<0.001) [20]. Möller et al. [31] studied the peculiarities of the functional state of kidneys at RA. It was found that GFR in such patients decreased by 0.83 mL/min per year (95% CI −1.08 to −0.57) [32,33]. The study of Hickson et al. [34] compared the weakening of renal function in 813 patients with RA and 813 patients without RA during the observation period of 20 years. It was found that RA is characterized by a decrease in GFR. The frequency of GFR decrease over 20 years was higher in patients with RA than those without RA (25.0% vs. 20.0%, p=0.03) [34].

5. Conclusion

Renal failure is a common systemic manifestation of RA, long and highly active course of which is an important trigger of rheumatoid nephropathy, which requires timely diagnosis and treatment of this complication. Patients with long-term RA and its high activity form a risk group for RA and need special attention. The most common morphological variant of nephropathy in RA in the studied patients was mesangial proliferative glomerulonephritis (48.4% of patients), secondary amyloidosis developed in patients (only 29.0% of patients) with a longer course of RA and its highest activity, indicating that the duration and activity of the disease affect the renal amyloidosis formation. The perspective of further research is to study cytokine profile characteristics in patients with RA according to the morphological variant of kidney disease.

Author contributions

Study concept and design: Yan Tang, Yuliya Varavko. Data acquisition: Yuliya Varavko, Raisa Aringazina. Data analysis: Raisa Aringazina, Irina Menshikova. Drafting of manuscript: Yan Tang, Irina Menshikova, Yuliya Varavko.

Critical revision of the manuscript: Yan Tang, Raisa Aringazina, Irina Menshikova.

Conflicts of interest

The authors declare no conflict of interest.