Question

• Discuss common causes of acute pyelonephritis, and describe the pathophysiology, clinical manifestations, evaluation, and treatment.

Answer 1

Causes

Bacteria that enter your urinary tract through the tube that carries urine from your body (urethra) can multiply and travel to your kidneys. This is the most common cause of kidney infections.

Bacteria from an infection elsewhere in your body also can spread through your bloodstream to your kidneys. Although it's unusual to develop a kidney infection, it can happen — for instance, if you have an artificial joint or heart valve that becomes infected.

Rarely, kidney infection results after kidney surgery.

Pathophysiology

Acute pyelonephritis results from bacterial invasion of the renal parenchyma. Bacteria usually reach the kidney by ascending from the lower urinary tract. ^[6] In all age groups, episodes of bacteriuria occur commonly, but most are asymptomatic and do not lead to infection. The development of infection is influenced by bacterial factors and host factors.^[7]

Bacteria may also reach the kidney via the bloodstream. Hematogenous sources of gram-positive organisms, such as Staphylococcus, are intravenous drug abuse and endocarditis. Experimental evidence suggests that hematogenous spread of gram-negative organisms to the kidney is less likely unless an underlying problem exists, such as an obstruction. Little or no evidence supports lymphatic spread of uropathogens to the kidney.

Clinical manifestation

Acute pyelonephritis results from bacterial invasion of the renal parenchyma. Bacteria usually reach the kidney by ascending from the lower urinary tract. ^[6] In all age groups, episodes of bacteriuria occur commonly, but most are asymptomatic and do not lead to infection. The development of infection is influenced by bacterial factors and host factors.^[7]

Bacteria may also reach the kidney via the bloodstream. Hematogenous sources of gram-positive organisms, such as Staphylococcus, are intravenous drug abuse and endocarditis. Experimental evidence suggests that hematogenous spread of gram-negative organisms to the kidney is less likely unless an underlying problem exists, such as an obstruction. Little or no evidence supports lymphatic spread of uropathogens to the kidney.

Management

Patients who are systemically unwell will require management in an A to E approach and appropriate resuscitation.

Start empirical antibiotics based on local protocols and IV fluids as appropriate, also prescribing suitable analgesia and anti-emetics. Tailor antibiotic therapy once sensitivities are available.

Whilst many uncomplicated cases can often be treated in the community, consider admission in those cases who are clinically unstable, significant dehydration, or with co-morbidities such as diabetes mellitus, renal transplant graft, immunocompromised.

Severe or non-responding cases may warrant catheterisation and high-dependency unit monitoring, as such cases can becoming profoundly and rapidly unwell. Consider early CT imaging* in such cases to check for obstruction and complications of pyelonephritis, such as of pyonephrosis (infected obstructed kidney) or a perinephric abscess.