Which statement best differentiates acute pyelonephritis from chronic pyelonephritis?

• A. Acute pyelonephritis features scarring and CKD; chronic is acute infection with fever
• B. Acute pyelonephritis presents without fever; chronic with fever
• C. Acute pyelonephritis is a chronic condition with gradual onset; chronic is acute with severe symptoms
• D. Acute pyelonephritis is an acute bacterial infection of the kidney with fever and costovertebral angle tenderness; chronic pyelonephritis involves scarring and functional loss from recurrent infections or obstruction

Answer: (D)

The key idea is how the two forms differ in cause, presentation, and long-term kidney damage. Acute pyelonephritis is an active bacterial infection of the kidney, typically presenting with fever and costovertebral angle tenderness as part of an acute inflammatory process. It’s an immediate infection that can respond to antibiotics and may not involve permanent changes in the kidney unless complications occur.

Chronic pyelonephritis, on the other hand, is a long-standing condition where repeated infections or chronic obstruction lead to scarring of the kidney tissue and progressive loss of function. Because the damage stems from ongoing scarring, fever is not a defining feature and the kidney may appear small or scarred on imaging, with signs of reduced function or CKD over time.

So the best differentiator is the statement that describes an acute bacterial kidney infection with fever and CVA tenderness, versus chronic pyelonephritis as scarring with functional loss from recurrent infections or obstruction. The other options misstate fever presence, duration, or the underlying nature of chronic disease.