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Difficulty: EasyFormulating a Differential Diagnosis

A 25-year-old woman presents to the clinic with a 3-day history of dysuria, urinary frequency, and suprapubic discomfort. She is sexually active with a new partner. Vital signs are normal, and she is afebrile. Physical examination reveals mild suprapubic tenderness but no costovertebral angle (CVA) tenderness. Arrange the following differential diagnoses in order from the most likely (highest pre-test probability) to the least likely for this patient's acute presentation.

  1. 1Uncomplicated acute cystitis
  2. 2Chlamydia trachomatis urethritis
  3. 3Acute pyelonephritis
  4. 4Interstitial cystitis

Answer

The correct sequence from most likely to least likely is: Uncomplicated acute cystitis, followed by Chlamydia trachomatis urethritis, Acute pyelonephritis, and finally Interstitial cystitis.
The correct ordering accurately reflects established clinical pre-test probabilities. Uncomplicated acute cystitis is the overwhelmingly most common cause of these localized, acute symptoms. STI-related urethritis serves as a strong secondary consideration due to the patient's sexual history. Pyelonephritis is a much lower probability without systemic infectious signs, and interstitial cystitis is incorrect to suspect during a 3-day acute presentation.

Step-by-Step Solution

1
Analyze the patient's symptoms and acuity.
The patient has localized lower urinary tract symptoms (dysuria, frequency, suprapubic pain) lasting for a short duration of 3 days.
Establishing symptom acuity and localization is the first step in formulating a clinical differential diagnosis.
2
Identify the most probable cause based on epidemiological frequency.
Uncomplicated acute cystitis is identified as the highest probability.
It is by far the most common cause of acute lower urinary symptoms in young, afebrile women.
3
Evaluate secondary diagnostic possibilities based on provided risk factors.
Chlamydia urethritis is placed second.
Having a new sexual partner increases the risk of sexually transmitted infections causing urethritis, though it remains less statistically common than standard cystitis.
4
Rule down diagnoses that lack required clinical features.
Acute pyelonephritis is ranked third.
The absence of upper urinary tract signs (such as fever and costovertebral angle tenderness) significantly lowers its pre-test probability.
5
Place chronic conditions at the bottom for an acute presentation.
Interstitial cystitis is ranked last.
By definition, this diagnosis requires chronic symptoms lasting over 6 weeks, making it highly unlikely for an acute 3-day history.

Key Concept

Prioritization of differential diagnoses for acute dysuria based on epidemiological frequency, risk factors, and symptom duration.
Estimated Time:1m 0s
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Topics

Formulating a Differential Diagnosis

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