Diagnosis and investigation of chronic kidney disease in cats

Symmetric Dimethylarginine is a Promising Biomarker for the Early Detection of Age-Related Kidney Dysfunction in Zoo Felids

Chronic renal failure is one of the leading causes of death in African lions, cheetahs, and tigers. Conventional methods to measure renal dysfunction include measuring serum creatinine and blood urea nitrogen (BUN). Symmetric dimethylarginine (SDMA) measurement is a reliable predictor of renal dysfunction in the domestic cat because SDMA serum levels increase early when the kidneys are damaged. Serum SDMA levels were assessed and correlated with creatinine as well as BUN from healthy captive Bengal tigers and lions at the Everland Zoo in Korea. Serum SDMA concentrations were increasingly associated with increased age in lions. However, SDMA concentrations were higher in some young Bengal tigers than in older ones, which may allow for earlier renal dysfunction detection in these young cats than would be BUN and creatinine alone. In Bengal tigers, the correlation between the SDMA and BUN was slightly higher than that between SDMA and creatinine. In lions, SDMA correlated better with creatinine than with BUN concentration. These results show that serum SDMA concentration can be used as a biomarker for age-associated renal dysfunction. SDMA measurement may be an essential preventive management method in zoos.

Blood concentration of symmetric dimethylarginine correlates with kidney damage as assessed with a proposed histologic grading system for chronic kidney disease in tigers (Panthera tigris)

OBJECTIVE

To determine the utility of blood symmetric dimethylarginine (SDMA) concentration measurement as a diagnostic tool for chronic kidney disease (CKD) in tigers (Panthera tigris) by comparing results for SDMA with those for traditional renal biomarkers and investigating correlations between these biomarkers and histopathologic kidney changes in tigers with CKD.

SAMPLE

Blood, urine, and kidney samples from 35 tigers with CKD from 2 sanctuaries.

PROCEDURES

Blood (serum or plasma) and urine samples were collected antemortem. Necropsy, including gross and histologic assessment, was performed for tigers that died or were euthanized for quality-of-life reasons. Results for CKD biomarkers in blood (BUN, creatinine, phosphorus, and SDMA concentrations) and urine (protein concentration, urine protein-to-creatinine ratio, and urine specific gravity) were evaluated for correlation with histologic kidney damage scored with an objective grading scale defined by percentage of inflammation, fibrosis, and tubular atrophy.

RESULTS

Symmetric dimethylarginine had the strongest significant correlation (ρ = 0.667) with histologic kidney damage score, followed by urine specific gravity (ρ = -0.639), blood creatinine concentration (ρ = 0.624), and BUN (ρ = 0.588). No significant correlation with kidney score was identified for blood phosphorus concentration, urine protein concentration, or the urine protein-to-creatinine ratio.

CLINICAL RELEVANCE

We recommend SDMA be prioritized as a renal biomarker in tigers, with SDMA results considered in addition to those of other traditional renal biomarkers when assessing kidney function in tigers. Additionally, the grading scale we developed could be replicated across patients and pathologists for more consistent postmortem assessment of CKD in tigers.

First detection of Feline morbillivirus infection in white-eared opossums (Didelphis albiventris, Lund, 1840), a non-feline host

Feline Morbillivirus (FeMV) was first detected in 2012 in domestic cats from Hong Kong and was found to be associated with tubulointerstitial nephritis and chronic kidney disease. In subsequent studies in other countries, FeMV was detected in asymptomatic cats. However, it is not clear whether FeMV plays a role as a pathogen in the kidney diseases of cats, and other epidemiological data are still unknown. To date, studies have reported the presence of FeMV exclusively in domestic cats. This study is the first molecular detection of the FeMV RNA associated with pathological and immunohistochemical findings in a synanthropic marsupial, the white-eared opossum (Didelphis albiventris), inhabiting peri-urban areas of north-central Parana, Southern Brazil. Molecular techniques identified the viral RNA in the lungs and kidneys. Histopathologic evaluation of these tissues revealed interstitial pneumonia in the lungs with lymphocytic nephritis and tubular necrosis in the kidneys. Immunohistochemistry assays detected positive intralesional immunoreactivity to N protein of FeMV within the lungs and kidneys. A FeMV opossum strain was isolated in Crandell Rees feline kidney lineage cells, resulting in syncytia formation and cell death. Therefore, these results support the ability of FeMV to infect other mammal species and reinforce the possibility of the opossum to be a disseminator of this virus among domestic and wild animals.

What outcomes should be measured in feline chronic kidney disease treatment trials? Establishing a core outcome set for research

Chronic Kidney Disease (CKD) is an important cause of feline morbidity and mortality. There is currently no agreement on which outcomes are most important in CKD treatment trials to assist evidence-based decision making. Core Outcome Sets (COSs) originated in human healthcare and are an agreed set of outcomes to be measured and reported as a minimum in any trial conducted relating to a particular disease. To establish a COS for feline CKD, this study used a systematic review and two consensus methodologies (an electronic Delphi (eDelphi), and an in-person consensus meeting), with an international panel of key stakeholders. The systematic review identified 104 unique published parameters, which were rated by panellists in round 1 of the eDelphi. Panellists were also asked to suggest additional parameters. In round 2 these additional parameters were rated and any parameters not understood by >10 % of panellists in round 1 were redefined and re-rated. Parameters reaching consensus in rounds 1 and 2 were removed from round 3, when all remaining parameters were re-rated by panellists who could view their own previous rating alongside the median rating of the whole panel. To reach inclusion in the COS, parameters had to be rated 8 or 9 on a Likert scale of 1-9 (where 1 was not important and 9 was very important) by more than 80 % of panellists. In the consensus meeting, panellists discussed and re-rated borderline parameters and streamlined the final COS. Borderline parameters were those that had been closest to, but not achieved, the 80 % threshold for inclusion. The eDelphi panel (n = 73) rated 24/104 parameters highly enough for inclusion and proposed an additional 20 parameters, of which 3 reached the inclusion threshold. This totalled 27 parameters for inclusion. The consensus meeting panel (n = 16) rated an additional 6/20 borderline parameters highly enough for inclusion. During the streamlining process, 4 parameters were removed as one was considered not an outcome, and three were already addressed by other parameters. The remaining COS totalled 29 parameters. These were grouped into 9 core themes: clinical examination, quality of life, serum biochemistry, complete blood count, urinalysis, total amount of food eaten, CKD progression, survival time and cause of death. This is the first COS for feline medicine. In future treatment efficacy trials the COS will strengthen the evidence-base for this condition, by facilitating easier comparison of results between studies, and reduce research waste.

Risk factors associated with disturbances of calcium homeostasis after initiation of a phosphate-restricted diet in cats with chronic kidney disease

BACKGROUND

Dietary phosphate restriction improves survival in cats with chronic kidney disease (CKD). However, feeding a phosphate-restricted diet may disrupt calcium homeostasis leading to hypercalcemia in some cats.

OBJECTIVES

To identify risk factors associated with increasing plasma total calcium (tCa) concentration after transition to a phosphate-restricted diet and to explore its role in CKD-mineral and bone disorder (CKD-MBD) in cats.

ANIMALS

Seventy-one geriatric (≥9 years) euthyroid client-owned cats with International Renal Interest Society (IRIS) stage 2 to 3 azotemic CKD.

METHODS

Retrospective cross-sectional cohort study. Changes in plasma tCa concentration in the first 200 days of diet transition were assessed using linear regression. Binary logistic regressions were performed to identify risk factors for increasing calcium concentration. Changes in clinicopathological variables associated with CKD-MBD over time were explored using linear mixed model and generalized linear mixed model analyses.

RESULTS

Lower baseline plasma potassium (odds ratio [OR] = 1.19 per 0.1 mmol/L decrease; P = .003) and phosphate (OR = 1.15 per 0.1 mmol/L decrease; P = .01) concentrations remained independent risk factors for increasing plasma tCa concentration. Plasma creatinine (β = .069 ± .029 mg/dL; P = .02), symmetric dimethylarginine (β = .64 ± .29 μg/dL; P = .03), phosphate (β = .129 ± .062 mg/dL; P = .04), and ln[FGF23] (β = .103 ± .035 pg/mL; P = .004) concentrations had significantly increased rates of change in cats with increasing plasma tCa concentration over time.

CONCLUSION AND CLINICAL IMPORTANCE

Lower plasma potassium or phosphate concentrations or both at the time of transition of cats with CKD to a phosphate-restricted diet are independently associated with increased risk of an increase in plasma tCa concentration. Increasing plasma tCa concentration is associated with progression of CKD.

Plasma symmetric dimethylarginine and creatinine concentrations and glomerular filtration rate in cats with normal and decreased renal function

Background

Glomerular filtration rate (GFR) is the gold standard in assessing renal function but is impractical. Serum creatinine (sCr) has limited sensitivity in identifying early chronic kidney disease (CKD), whereas symmetric dimethylarginine (SDMA) has been commercialized as more accurate biomarker. Studies comparing SDMA and sCr with GFR in cats are limited.

Objectives

To further investigate the diagnostic performance of SDMA in nonazotemic and azotemic cats.

Animals

Forty‐nine client‐owned cats: 17 cats with CKD, 15 cats with diabetes mellitus (DM), and 17 healthy cats.

Methods

Retrospective study using spare blood samples from cats with documented sCr and GFR results for SDMA analysis. Diagnostic performances of SDMA and sCr were evaluated using correlation coefficients, sensitivities, specificities, and receiver operator characteristic curves.

Results

Compared to healthy cats and cats with DM, CKD cats had significantly higher SDMA_plasma (26.7 ± 9.9 μg/dL) and sCr (249.7 ± 71.6 μmol/L [2.8 ± 0.8 mg/dL]; both P < .001) values. SDMA_plasma (τ_B = −0.57; P < .001) and sCr (τ_B = −0.56; P < .001) were significantly correlated with GFR. SDMA_plasma (τ_B = 0.52; P < .001) had a significant relationship with sCr. SDMA_plasma and sCr had similar sensitivity (76%‐94% and 71%‐88%, respectively) in detecting reduced renal function. Creatinine had higher specificity (94%‐96%) than SDMA_plasma (75%‐76%) (P < .05).

Conclusion and Clinical Importance

In this study of azotemic and nonazotemic cats, SDMA was a reliable marker to identify decreased GFR. However, superiority of SDMA over sCr could not be confirmed.

Polycystic kidney disease concurrent with feline parvovirus and bacterial infections in domestic shorthair cat: a case report

Feline polycystic kidney disease (PKD) is an inherited disorder caused by the mutation of PKD1 gene that eventually lead to the development of chronic kidney disease. The latter condition causes hypertension and eventually progress into congestive heart failure. Feline parvovirus (FPV) is a highly contagious and often fatal disease infecting cats and other members of Felidae. An 8-month-old female domestic shorthair cat was presented with complaint of wound dehiscence a day after ovarian hysterectomy procedure. The wound at the suture site appeared necrotic, purulent with foul smell. The cat was found to have diarrhoea during the fixation of suture breakdown and, later, was tested positive with parvovirus infection. Complete blood count revealed anaemia, neutrophilia, lymphopenia and thrombocytosis. Biochemistry profiles showed hypoproteinaemia and elevated of urea and creatinine. The cat was hospitalised, and symptomatic treatments were given. During hospitalisation, the cat showed symptoms of polydipsia and polyuria and found dead 2 days later. Post-mortem findings demonstrated the cat had oral ulceration, thoracic effusion, fibrinopleuropneumonia, pericardial effusion, left ventricular hypertrophy and right ventricular dilation, chronic passive liver congestion, mesenteric lymphadenomegaly, intestinal haemorrhage, adrenomegaly and polycystic kidney. Histopathological evaluation revealed fibrinous pleuropneumonia, pulmonary atelectasis, emphysema and oedema, hypertrophic cardiomyopathy, hepatic necrosis, splenic necrosis, intestinal necrosis, renal necrosis and renal polycystic. Staphylococcus aureus and Escherichia coli were isolated from bronchus swab and intestinal segment, respectively. Polymerase chain reaction (PCR) revealed parvovirus infection. The cat was definitely diagnosed with polycystic kidney disease concurrent with parvoviral and secondary bacterial infections.

Clinical outcomes of 28 cats 12-24 months after urethrostomy

OBJECTIVES

The aim of this study was to evaluate and compare the long-term clinical outcomes and quality of life of cats having undergone perineal urethrostomy (PU) or prepubic urethrostomy (PPU).

METHODS

This clinical study followed 28 cats (PU, n = 22; PPU, n = 6) that underwent a urethrostomy, with a minimum of 1 year postoperative follow-up. Medical records, pet owner surveys and urologic laboratory tests were used for assessment. Urologic laboratory tests included serum symmetric dimethylarginine (SDMA), serum creatinine, urinalysis, urine specific gravity (USG), urine protein:creatinine (UPC) ratio and urine culture.

RESULTS

The main indications for urethrostomy were multiple catheterizations and PU stricture. The overall complication rates of PU and PPU were 31.8% and 83.3%, respectively. Recurrent urinary tract infection (UTI) and urine scald dermatitis were less frequent in PU than in PPU cats (UTI 22.7% vs 66.6%; dermatitis 4.5% vs 83.3%). Bacteriuria was present in 77.2% and 100% of PU and PPU cats, respectively. Owner satisfaction rates were excellent in 81.8% of PU and 33.3% of PPU cases.

CONCLUSIONS AND RELEVANCE

A proportion of cats that underwent urethrostomy showed bacteriuria, recurrent UTIs and increased levels of SDMA. PPU is important as a salvage procedure; however, it should be limited to cases in which standard techniques for PU cannot be performed, owing to the potential for recurrent complications and lower owner satisfaction.

A nutraceutical diet based on Lespedeza spp., Vaccinium macrocarpon and Taraxacum officinale improves spontaneous feline chronic kidney disease

Chronic kidney disease is characterized by structural and/or functional impairment of one or both kidneys persisting for more than 3 months. In cats, chronic kidney disease can frequently occur in animals aged over 9 years with an incidence of approximately 10%. Thirty-four client-owned, neutered cats, suffering from stage II-III chronic kidney disease and diagnosed according to the International Renal Interest Society guidelines were randomly assigned to receive either a control diet (n = 17) or a nutraceutical diet (ND; n = 17) for 90 days. Both diets were commercialized for management of CKD symptoms. The diets were identical except that the ND contained tablets that consisted of 60-80% hydrolysed proteins, 20-40% minerals and active substances, that are, Lespedeza spp. 0.0588%, Vaccinium macrocarpom 0.0371%, and Taraxacum officinale 0.0231%. No adverse effects were reported during this study. Both diets resulted in an improvement in CKD symptoms. After a 90-day evaluation, creatinine, blood urea nitrogen, total proteins, and aspartate aminotransferase significantly decreased in cats that received the ND. A significant decrease was also observed in urine turbidity score, color score, and total proteins in cats that received the ND. We have found that a ND based on Lespedeza spp., Vaccinium macrocarpon, and Taraxacum officinale improves key indicators of renal failure in cats affected by chronic kidney disease.