Chronic kidney disease (CKD) is reported in 1-3% of cats with an estimated one-third of cats developing CKD in their lifetime. In the US, 15% of adults, 37 million people, have CKD. In both cases, the disease prevalence increases with age: an estimated 38% of people over 65 years old and approximately 30% to 80% of cats over 15 years old live with CKD. While glomerular disease, damage directly to the glomeruli, is usually the primary cause of CKD in humans and dogs, it is quite rare in cats. In feline patients tubulointerstitial fibrosis, deposition of connective tissue in the functional portions of the kidney, is the primary cause of CKD. However, in all species the final common pathways for CKD is thought to be renal fibrosis and hypoxia. There is no effective treatment that slows the progression of renal fibrosis for either cats or humans. Although there are similarities between the disease in these species, a significant difference exists in the etiology of CKD. In humans, the two primary causes are Type 2 diabetes and hypertension while in cats it is often of idiopathic origin.
Hypertension and diabetes are leading causes of human CKD. Diabetes has not been identified as a risk factor for feline CKD, and hypertension appears to be a complication rather than etiology of feline CKD. Less common causes of CKD in both species include congenital kidney malformations (e.g. polycystic kidney disease), genetic diseases (e.g. amyloidosis), neoplasia, immune-mediated inflammation, infection, toxins, and ischemia. Unlike in humans, many feline CKD cases are idiopathic with non-specific tubulointerstitial inflammation and fibrosis. In areas of Central America, Europe, and Asia there are reports of idiopathic tubulointerstitial disease in humans, particularly sugar cane workers. High temperatures may cause repeated episodes of acute kidney injury (AKI) in these individuals as chronic dehydration and repeat episodes of AKI may be a cause of feline CKD. Age related changes (telomere shortening, loss of repair functions) also likely play a role in feline CKD as incidence greatly increases with age.
Shared clinical signs/associated conditions of CKD include polyuria, anorexia, lethargy, anemia, hypertension, nausea/vomiting, weight loss, renal secondary hyperparathyroidism, hyperkalemia, kidney stones, pyelonephritis, proteinuria, and hyperphosphatemia. Cats may have poor hair coat, polydipsia, halitosis, and constipation, while humans may experience insomnia, decreased mental acuity, muscle cramps/twitching, peripheral edema, GI ulcers, and persistent itching. Detection and staging of CKD involves blood tests to measure BUN and creatinine, urinalyses to assess specific gravity and proteinuria, and blood pressure monitoring. Imaging is used to identify kidney abnormalities. Glomerular filtration rate and kidney biopsy are often performed in humans but less frequent in cats. Studies are ongoing to determine if SDMA, used in veterinary medicine for early CKD detection, is reliable in humans. Urinary cytokines may be indirect measures of renal inflammation, directly correlate to kidney function, and serve as a non-invasive test for CKD progression.
CKD is a serious, life-threatening disease in both humans and cats. Treatments have traditionally focused on managing symptoms and slowing disease progression, including diet changes and medications to lower blood pressure, treat anemia, bind phosphate, and inhibit the renin-angiotensin-aldosterone system. Symptom management in cats often includes subcutaneous fluids, anti-nausea medications, and appetite stimulants. For severe cases, dialysis and kidney transplants are used primarily in humans and less commonly in cats. Dogs and humans tend to have proteinuria early in the disease process due to underlying glomerular disease, so angiotensin converting enzyme inhibitors and angiotensin receptor blockers are commonly used; feline patients usually present with proteinuria later in disease. Recent advances in treatments for CKD include new therapeutics to treat anemia and immunosuppressants to aid in kidney transplants. Research is ongoing to evaluate the potential for stem cell therapy to help restore kidney function, and CRISPR technology is being studied as a potential therapy when kidney disease has a genetic etiology.
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