• Acute infection of renal pelvis or parenchyma

• Abscess formation but sparing of glomerulus
• May be asymptomatic (rarely)
• Classical presentation is with chills, fever, nausea, vomiting, and unilateral or bilateral loin pain radiating to iliac fossae and suprapubic area
• Fever and loin pain are frequently also present in uncomplicated lower UTI and may be absent in pyelonephritis
• Lumbar tenderness and guarding are usual
• Dysuria, frequency, and urgency due to associated cystitis occur in 30%
• Septicemia, shock, and hypotension may supervene in severe cases
• Urine microscopy reveals erythrocytes and leukocytes, leukocyte casts if renal parenchyma is involved, organisms, and epithelial cells
• Children may present with fever alone or with vomiting, apathy, convulsion, abdominal distension, irritability, poor perfusion, poor color, flank mass, enuresis, diarrhea, or vulval pruritus
• In the absence of urinary tract abnormalities, pyelonephritis rarely leads to serious chronic renal disease after the age of 5 years
• May rarely result in acute papillary necrosis or, in the presence of obstruction, may progress to chronic pyelonephritis

TO BE CONTINUED