Chronic pyelonephritis (CP) is marked by chronic renal tubulointerstitial inflammation which leads to scarring within the renal cortex and calyceal clubbing. It may lead to end-stage renal disease (ESRD). The disease is also known as reflux nephropathy, interstitial nephritis, and chronic atrophic pyelonephritis. CP also includes rare variants like xanthogranulomatous pyelonephritis (XGP) and emphysematous pyelonephritis (EPN) [1]. The clinical presentation of CP is variable and non-specific. Some patients may be asymptomatic while others may present with malaise, fatigue, loss of appetite, loss of weight, cloudy urine, fever, backache, flank pain, or abdominal discomfort. In advanced stages of the disease, patients will have hypertension. XGP may be characterized by the presence of a unilateral palpable abdominal mass, while patients with EPN may present with signs of sepsis.

Chronic pyelonephritis may follow inadequate treatment or recurrence of acute pyelonephritis, composed of a localized immune response to bacteria that have been eradicated [2]. In children, the chief cause of CP is vesicoureteral reflux (VUR) and recurrent urinary tract infections (UTIs) associated with renal scarring [3] [4]. In adults, renal scarring is rarely due to urinary tract infections [5] [6].

Xanthogranulomatous pyelonephritis (XGP) is a rare variant of CP and may be associated with longstanding obstructive urinary tract disorders and Proteus infection [7].

Emphysematous pyelonephritis (EPN) is another rare, potentially life-threatening variant of CP. The disease develops secondary to renal parenchymal infection with E.coli, Klebsiella, or Proteus species. It is characterized by a sudden onset of acute necrotizing pyelonephritis and the presence of a renal parenchymal gas, usually in poorly controlled diabetics [8].

The diagnosis of CP can be difficult due to its variable and often vague clinical presentation. It can be suspected in patients who provide a history of renal calculi, recurrent UTIs, acute pyelonephritis or VUR. Occasionally the diagnosis is suspected based on incidental radiological findings or in patients presenting with hypertension. Laboratory tests like a complete blood count may reveal normochromic, normocytic anemia with leukocytosis. C-reactive protein (CRP) may be elevated in severe CP [9]. Urinalysis is likely to show hematuria, proteinuria, leukocytes with occasional epithelial cells, and rarely WBC casts. The severity of renal dysfunction can be estimated by renal function tests like serum creatinine, blood urea nitrogen, and estimated glomerular filtration rate [10]. Depending on the extent of renal damage there will be electrolyte imbalances like hyperkalemia, hyponatremia, and acidosis. Renal imaging is performed to detect the etiology of CP. Currently, magnetic resonance imaging (MRI) and computed tomography (CT) provide detailed information and are preferred over older modalities like plain X-rays, urography, and Tc-99m-DMSA nuclear scintigraphy, as well as histology [11]. In children, an ultrasound and a cystourethrogram are performed to exclude VUR [12].

Xanthogranulomatous pyelonephritis (XGP): Proteus, and less commonly Escherichia coli, Klebsiella, and Staphylococcus aureus, are found in urine cultures. Imaging studies like CT and MRI may detect a renal mass resembling a tumor [13]. However, the final diagnosis of XGP is based on histology of the nephrectomy specimen [13] [14].

Emphysematous pyelonephritis (EPN): Laboratory tests can show leukocytosis with elevated CRP [15], elevated blood glucose, and HbA1C levels. Blood and urine cultures may grow Escherichia coli, Klebsiella, or Proteus species. Gas may be noticed within the renal parenchyma on plain X-rays and ultrasound, while CT or MRI scans are useful in diagnosing the disease extent. [1] [16] [17] .

The treatment of chronic pyelonephritis focuses on managing symptoms, preventing further kidney damage, and addressing any underlying causes. Antibiotics are often prescribed to treat or prevent infections. In cases where structural abnormalities contribute to the condition, surgical intervention may be necessary. Patients are also advised to maintain good hydration and follow a kidney-friendly diet. In advanced cases, dialysis or kidney transplantation may be required.

The prognosis for chronic pyelonephritis varies depending on the extent of kidney damage and the effectiveness of treatment. Early diagnosis and appropriate management can slow the progression of kidney damage and improve outcomes. However, if left untreated, chronic pyelonephritis can lead to chronic kidney disease and, eventually, kidney failure.

Chronic pyelonephritis is often caused by recurrent or persistent bacterial infections of the kidneys. Conditions that predispose individuals to these infections, such as vesicoureteral reflux (a condition where urine flows backward from the bladder to the kidneys) or urinary tract obstructions, can increase the risk. Other contributing factors include kidney stones, diabetes, and a weakened immune system.

Chronic pyelonephritis is relatively uncommon compared to acute kidney infections. It is more frequently diagnosed in women due to anatomical differences that make them more susceptible to UTIs. Children with urinary tract abnormalities and individuals with a history of recurrent UTIs are also at higher risk. The condition can occur at any age but is more prevalent in older adults.

The pathophysiology of chronic pyelonephritis involves repeated or persistent inflammation of the kidney tissue, leading to scarring and fibrosis (thickening and stiffening of tissue). This scarring disrupts normal kidney function, reducing the organ's ability to filter waste from the blood. Over time, the progressive damage can lead to chronic kidney disease.

Preventing chronic pyelonephritis involves reducing the risk of kidney infections and addressing any underlying conditions. This can include practicing good hygiene, staying well-hydrated, and promptly treating any UTIs. Regular medical check-ups and monitoring for individuals with known risk factors, such as urinary tract abnormalities, can also help prevent the condition.

Chronic pyelonephritis is a serious kidney condition resulting from long-term inflammation and infection. It can lead to significant kidney damage if not properly managed. Early diagnosis and treatment are crucial to prevent progression to chronic kidney disease. Understanding the risk factors and symptoms can aid in early detection and improve patient outcomes.

For patients, understanding chronic pyelonephritis is key to managing the condition effectively. It is important to recognize symptoms such as persistent back pain, fever, and changes in urination patterns. Regular follow-ups with healthcare providers, adherence to prescribed treatments, and lifestyle modifications can help manage the condition and maintain kidney health.

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