Overview 

In the human body, there are two kidneys, both are part of the urinary system, where they are responsible for filtering blood. The kidneys do not just have one function, they also:

• Filter waste from the blood 
• Balance  fluid concentrations in the blood
• Control blood pressure
• Assist in the reproduction of red blood cells
• Activate vitamin D
• Make sugar molecules
• Produce chemicals that assist kidney function.

A kidney condition called papillary necrosis will be explored in this article and compared to kidney stones. Papillary necrosis is where damage to the kidney causes structures in the organ to no longer properly drain urine into the bladder via the ureter (a tube that connects the kidney and bladder). However, kidney stones (renal calculi), are where ‘stone-like’ structures composed of salts and minerals, accumulate in the kidneys. The purpose of comparing these conditions is to highlight their similarities and differences in causes, symptoms, diagnosis, treatment strategies, and prognosis. 

What are Papillary necrosis and Kidney stones? 

What is Papillary Necrosis?

As briefly established in the introduction, renal papillary necrosis is a disease of the kidney where tissue and cell death occurs, preventing the organ from performing its vital role.

Normally, blood enters the kidney through the renal artery where waste and water is filtered by the Bowman's capsule before traveling to the kidney medulla. The filtered substance travels through the loop of Henle  (a funnel-like structure in the kidney) to the collecting duct, where urine is formed. Urine flows through the renal pyramids exiting via the renal papillae to the renal pelvis and ureter.

However, papillary necrosis prevents urine draining into the renal pelvis, as the renal papillae are damaged. This is the starting point of papillary necrosis and only gets worse if untreated.^1,2

What are Kidney Stones?

Kidney stones are harmful and solid, stone-like structures made of minerals, salts, waste products of proteins, and potassium. Different types of stones can develop:

Calcium stones

• Made from calcium and oxalate, these stones are associated with high levels of calcium in urine (hypercalciuria)
• Hypercalciuria results from excessive reabsorption of calcium
• Excess oxalate levels in the urine can also be a result of hypercalciuria, Crohn's disease, inflammatory bowel disease, or ulcerative colitis

Struvite stones

• Magnesium, ammonium, phosphate, and calcium carbonate create these stones
• Ammonia from bacterial infections, helps form these stones creating alkaline urine³

Uric acid stones

• Uric acid is a component of proteins and appears in urine because of hypercalciuria^4,5
• Excess uric acid is a result of too much dietary protein (mainly from red meat or poultry) 
• Uric acid kidney stones have also been associated with gout

Cystine stones

• The most rare types of kidney stones since they usually develop in patients with genetic metabolic issues
• Proteins are made up of many single amino acids; cystine is one of the single amino acids
• Cystinuria is the presence of cystine in urine indicates cystine kidney stones⁶

Differences in causes of papillary necrosis and kidney stones

Causes of papillary necrosis 

Causes for the onset of papillary necrosis vary per patient. Some common hallmark characteristics which most individuals exhibit include:^2,7 

• Haematuria (blood in urine)
• Diabetes
• Overuse of NSAIDs (non-steroidal anti-inflammatory drugs)
• Flank pain
• Urinary tract infection symptoms
• Fever and chills (if infection is present)
• Sickle cell disease
• Chronic liver disease
• Pyelonephritis - kidney infection
• Renal tuberculosis - tuberculosis in the kidney
• Renal vein thrombosis - a vessel that takes blood away from the kidney is clotted
• Ureteral obstruction - blocking of the ureter (the tube that connects the bladder and kidney)
• Vasculitis - blood vessel inflammation
• Dysuria

Causes of kidney stones

Similarly, kidney stones are caused from both genetic and environmental factors. 

Listed below are the four main causes of kidney stones:

• Dehydration
• Diet (high in oxalates, sodium, protein)
• Family history
• Certain medical conditions (e.g., hyperparathyroidism)

Comparing causes 

It is clear that there are overlaps from the causes listed for both disorders above, however, the fundamental pivotal factors that affect the onset development of these diseases are very different. These differences are conveyed by those points not shared amongst the list of causes.

How do papillary necrosis and kidney stones differ pathophysiologically?

Defining pathophysiology

Pathophysiology is understanding how the body is physiologically impacted and how the impact induces any changes caused by or associated with any pathogens, disease, or injury.

Pathophysiology of papillary necrosis

The renal papillae can be damaged very easily by a number of factors that can trigger papillary necrosis, furthermore when damaged, the necrosis can cause the onset of other issues too:^2,4

• Diabetes 
• Urinary tract infections (UTIs)
• Sickle cell disease
• Obstruction of the urinary tract

Pathophysiology of kidney stones

Kidney stones can affect a patient's body in different ways and it leads to many other diseases if undiagnosed and untreated. 

• Stones develop between the kidneys’ nephron and renal pelvis at the papilla, similar to papillary necrosis. Over time, minerals and salts accumulate forcing the stone to sometimes penetrate the renal pelvis and occasionally obstruct the ureter. This prevents urine flow to the bladder⁶
• In some patients, the development of kidney stones (regardless of what types they are) cause the urinary system to be damaged. This manifests as decreased urine production, and urine with abnormally high concentrations of minerals and salts⁶

Pathophysiological comparison

The pathophysiology of both conditions is somewhat similar, this is because kidney stones and papillary necrosis develop near the renal papilla. Additionally, both lead to localised urinary system disorders and infections, however, papillary necrosis, also has a large ‘global’ effect on the body by increasing the risk for diabetes, and sickle cell disease.⁸

Differences in symptoms

Symptoms of papillary necrosis

Symptoms of papillary necrosis range across a spectrum, their nonspecific nature creates difficulties during diagnosis. More defined symptoms come about as necrosis progresses making diagnosis easier.¹

• Nocturia - excess urination at night
• Dysuria - painful urination
• Pyuria 
• Haematuria - blood in urine
• Ureteral colic
• Back pain
• Blood or cloudy urine
• Pieces of tissue found in urine

Symptoms of kidney stones

Different types of kidney stones have unique symptoms. Some common symptoms include:

• Fevers / severe fluctuation in temperature
• Sweating 
• Severe pain (back, sides, and lower abdomen)
• Haematuria
• Nausea and vomiting
• Frequent urination
• Pain and blood during urination

Comparing the symptoms 

Similar to pathophysiology, symptoms in both conditions overlap. Both affect the renal papillae, triggering shared symptoms like back pain, urine abnormalities, and damage to the urinary system. This could be due to both conditions targeting the same tissue, which explains the similar urinary system symptoms.

Diagnostic techniques for papillary necrosis and kidney stones

Diagnosis for papillary necrosis and kidney stones 

A number of diagnostic techniques assist observing and identifying hallmark physiological traits for both conditions. Diagnostic techniques include imaging strategies, urinalysis, or biopsies.⁹

There are three imaging techniques which are used for diagnosis.¹⁰

• Intravenous pyelogram (IVP) is a type of X-ray method used to visualise the kidney, ureter, and bladder by injecting a contrast dye to assist in the visualisation of these organs as it travels through the body’s urinary system¹¹
• Ultrasound is used to visualise the urinary system using high-frequency sound waves to outline these organs
• Computer tomography (CT) scans are used to visualise the urinary system in three dimensions by using X-rays to image organs and a computer program to formulate a 3D image of all the organs together¹¹ 

CT scans are the preferred imaging technique because they are more intricate, descriptive with more clarity, and higher quality than other imaging techniques. This allows for in-depth analysis of organs to be conducted.¹⁰

The second diagnostic technique is Urinalysis. This involves chemical examinations on urine to detect traces, markers, and molecules that are signs of papillary necrosis or different types of kidney stones. 

In both conditions, a number of molecules and traces act as hallmark flags seen in urine. This is because both conditions damage the urinary system so abnormalities in urine will indicate an issue.

Blood tests are also conducted to check for high levels of certain minerals or substances in kidney stones.

Both papillary necrosis and kidney stones use the same diagnostic techniques, however, what is being searched for in the patient differs due to the conditions pathophysiological differences.¹²

Evaluating the comparisons in symptoms, pathophysiology, causes, and diagnosis

As different as both conditions are in physiology and causes, there are some very clear symptoms and diagnostic techniques which are almost identical in both conditions. This can prove to be an issue because the overlap can cause errors in diagnosis, as these disorders can easily be mistaken for each other.

Summary

To summarise papillary necrosis is where there is damage to the papilla near the renal pyramid however, kidney stones are where salts and minerals solidify into stones near the renal papillae, both conditions prevent urine from draining into the bladder.  

Some clear overlaps in both conditions include their diagnostic techniques: CT scans, ultrasounds, and urinalysis despite targeting different issues. Similarly, both share symptoms regarding urinary system abnormalities, but independant symptoms of papillary necrosis also include nocturia and tissue in the urine whereas kidney stones trigger severe pain and fevers. Causes also differ since papillary necrosis has been associated with diabetes, NSAID overuse, and infections, but kidney stones are linked to dehydration, dietary, and genetic causes.