Introduction

The kidneys play a crucial role in maintaining overall health. They are responsible for filtering the blood of excess water, toxins, and waste products. The kidneys have a highly specialised structure that allows them to optimise their blood-filtering function. The outer kidney region is known as the cortex, and the inner region is the medulla. Nephrons are found within both the cortex and medulla, and it is within the nephrons that the concentration of water and small molecules is controlled by filtration. The medulla is composed of between 8 and 12 renal pyramids, and the renal papillae are found closest to the inner curve of each kidney. These papillae are crucial, as they lead to the calyx and form the first part of the urine-collecting pathway, which ends at the bladder.

Papillary necrosis is a condition in which cells and tissues within the renal papillae die to a point where their function in collecting urine is negatively affected.¹ If sufficient kidney tissue is damaged, this can lead to kidney failure. Chronic Kidney Disease (CKD) is a progressive condition that can worsen over time due to a number of risk factors that alter the structure and function of the kidney. Since papillary necrosis involves cell and tissue death, there is an important link between the two conditions, where papillary necrosis may contribute to the development of CKD in many cases.

Papillary Necrosis

In papillary necrosis, the cells and tissues that form the normal structure of the urine-collecting pathway are progressively lost. This is a serious issue and can lead to a build-up of urine within the kidney. Urine contains harmful waste products that must be expelled from the body. In 70% of cases, both kidneys are affected.¹ One cause of papillary necrosis is ischaemia, in which cells lack the oxygen needed to function normally. Any drug or chemical compound that is harmful to the renal papillae is referred to as a nephrotoxic agent, and such agents also contribute to the development of papillary necrosis.² The environment surrounding the nephrons is known to be hypertonic (characterised by a higher ion concentration, such as salts), which increases osmotic pressure and can further promote necrosis. As papillary tissue becomes dysfunctional, it can dislodge from the pyramids and slough into the urine-collecting pathway, leading to obstruction of the collecting ducts.⁴ Over time, these blockages can result in urinary tract infections, kidney stones, and a build-up of harmful waste products within the body.

There are many causes of papillary necrosis; however, the most common risk factors include:⁴

• Diabetes
• Analgesic overuse: Prolonged combined use of aspirin, paracetamol, and similar drugs
• Sickle cell disease
• Infections: The renal papillae can become a site of infection, such as tuberculosis or pyelonephritis

Urinary obstructions may also cause necrosis, as can inflammation of blood vessels within the renal papillae.¹ Urinary obstructions additionally arise as papillary necrosis worsens, creating a self-perpetuating cycle in which the condition continues to deteriorate.

The appearance of renal papillae in papillary necrosis can be assessed using radiological techniques such as sonography or CT scanning. On sonography, the signs of papillary necrosis vary with disease stage. In early stages, there may be only fluid visible in the medulla with ring structures present, whereas in later stages, cavities within the renal calyces may become apparent.² In addition to radiological findings, haematuria (the presence of blood in urine) and flank pain in the lower back or abdomen may be observed. Papillary necrosis in patients with sickle cell anaemia is particularly difficult to diagnose, as the characteristic ring signs are not always easily detected.⁴ It should be noted that these symptoms are shared by many other conditions, and it is therefore advisable to consult a doctor in the first instance.

Chronic Kidney Disease

CKD affects approximately 10% of the adult population and is a condition that worsens progressively if not properly managed. The kidneys can no longer function normally, and this may occur for a variety of reasons.³ If left untreated, CKD is associated with high morbidity, making it important to maintain a healthy lifestyle and follow appropriate treatment to prevent further deterioration of kidney function.

CKD is diagnosed using glomerular filtration rate (GFR) criteria. Essentially, the rate at which blood is filtered per unit area of the kidney is measured; if this value falls below 60 mL/min, the degree of kidney damage becomes considerably more serious. The stages of CKD are categorised based on estimated GFR (eGFR) values, as used to diagnose patients⁵, and are outlined in the table below:

Despite being a progressive disease, certain conditions increase the incidence and rate of CKD progression. Diabetes is a particularly common risk factor for end-stage renal disorders such as CKD and also raises the risk of other complications such as albuminuria and cardiovascular disease.⁶ Hypertension is another common risk factor, as elevated pressure within the kidney's filtration system contributes to damage. Glomerulonephritis, another condition associated with kidney damage, is also linked to CKD.

As CKD progresses, waste products accumulate in the kidneys and blood. This also increases the risk of conditions such as:³

• Hypertension (high blood pressure)
• Anaemia
• Electrolyte imbalances
• Mineral and bone disorders
• Metabolic acidosis (acidaemia)

As illustrated, some conditions that contribute to CKD are also caused by its progression, making it difficult to establish causation between risk factors and disease onset. Furthermore, studies indicate that CKD progression is not always linear, particularly in patients with a history of acute kidney injury,³ and it is therefore important to consult a doctor to determine the most appropriate course of action.

Management and Treatment

Both papillary necrosis and CKD have significant structural components to the progression of each disease. Early intervention is extremely important for maintaining a patient's quality of life, particularly for those with a family history of these conditions or who have known risk factors. Imaging techniques such as CT scans or MRI scans can assist doctors in assessing kidney structures and establishing a formal diagnosis, as symptoms in early stages may not be severe.

Managing kidney-related diseases can be achieved through both medication and lifestyle changes. Discontinuing the use of analgesic medicines such as paracetamol or aspirin² and reducing dietary sodium and protein intake are recommended for those with kidney-related disorders, particularly CKD.³ Managing conditions that are known risk factors is also important to prevent further kidney damage. Diabetes, as a recognised risk factor for both papillary necrosis and CKD, requires careful management to reduce further renal injury. A low-protein, plant-based diet has also been shown to be beneficial, especially for CKD.³ In patients with severely compromised filtration rates, dialysis may be recommended to prevent the accumulation of harmful waste products in the blood.

Summary

Papillary necrosis and CKD are conditions that affect the structure of the kidneys, impairing their ability to filter blood and function normally. They are linked by shared risk factors, including diabetes, hypertension, and cardiovascular disease. These risk factors may themselves develop as a consequence of papillary necrosis or CKD, which complicates the establishment of causation. The onset and progression of these diseases are more prevalent with advancing age, high-sodium diets, and obesity.³ Symptoms such as haematuria, an abnormal urine odour, or unexplained weight loss may indicate kidney problems, and radiological diagnosis can provide a clear assessment of affected areas and the extent of damage. Management of both papillary necrosis and CKD can be supported through lifestyle modifications, such as reducing protein and salt intake and addressing other conditions that are risk factors for disease progression.