Differential Diagnosis for a 33-year-old Female with 20 weeks Pregnancy, CVA Tenderness, and Dysuria

Single Most Likely Diagnosis

• Pyelonephritis: This is the most likely diagnosis given the patient's symptoms of costovertebral angle (CVA) tenderness, dysuria, and a urinalysis (UA) positive for leukocytes and nitrites, which are indicative of a urinary tract infection (UTI) that has ascended to the kidneys. Pyelonephritis is a common complication of UTIs, especially during pregnancy due to physiological changes that predispose to urinary stasis and infection.

Other Likely Diagnoses

• Cystitis: While the presence of CVA tenderness suggests upper urinary tract involvement, cystitis (infection of the bladder) cannot be ruled out without further evaluation. The symptoms of dysuria and a positive UA could also be consistent with cystitis.
• Kidney Stone: Although less likely given the UA results, a kidney stone could cause CVA tenderness and dysuria. However, the presence of leukocytes and nitrites in the UA makes this less likely.
• Pregnancy-related complications: Conditions such as placental abruption or preterm labor could potentially cause abdominal or back pain but would not typically cause dysuria or a positive UA for infection.

Do Not Miss Diagnoses

• Appendicitis: Although the symptoms do not classically suggest appendicitis, it is a condition that could present atypically, especially in pregnancy, and has significant morbidity if missed. The location of the appendix can vary, and in late pregnancy, it may be displaced upwards, potentially causing right upper quadrant or flank pain.
• Pre-eclampsia with HELLP syndrome: This condition can cause abdominal pain and could potentially be confused with pyelonephritis or other causes of abdominal pain. It is critical to assess blood pressure and perform appropriate laboratory tests to rule out pre-eclampsia.
• Sepsis: Any infection, including pyelonephritis, can lead to sepsis, a life-threatening condition. Early recognition and treatment of sepsis are crucial.

Rare Diagnoses

• Interstitial nephritis: This is an inflammation of the spaces between the renal tubules and is less common. It could be caused by an allergic reaction, certain medications, or infection, but it would be an unusual cause of the patient's symptoms.
• Renal infarction: This is a rare condition where the blood supply to the kidney is interrupted, leading to tissue death. It could cause severe flank pain and might be considered in the differential diagnosis, especially if there are risk factors for thromboembolic events.

ACOG Recommendations for Pyelonephritis

The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women with pyelonephritis be hospitalized for intravenous antibiotic therapy, especially if they are symptomatic or have a temperature greater than 100.4°F (38°C). Outpatient management may be considered for select patients who are asymptomatic or have mild symptoms, are compliant with treatment, and have ready access to medical care. The choice of antibiotic should be based on local resistance patterns and should cover common urinary pathogens.