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Question

Difficulty: MediumPhysical Examination Findings

A 49-year-old man comes to the clinic reporting a one-week history of worsening lower back and right flank pain, accompanied by subjective fevers and chills. He has a history of type 2 diabetes mellitus and recently recovered from a staphylococcal skin infection on his right thigh. His temperature is 38.4∘C38.4^\circ\text{C} (101.1∘F101.1^\circ\text{F}), blood pressure is 128/78 mm Hg128/78\text{ mm Hg}, and pulse is 98/min98\text{/min}. On physical examination, the patient prefers to lie supine with his right hip slightly flexed. Passive extension of the right hip elicits severe pain in the right flank and lower abdomen. However, passive internal and external rotation of the right hip while flexed do not cause significant discomfort. There is no costovertebral angle tenderness, and a straight-leg raise test is negative. Based on these physical examination findings, which of the following is the most likely diagnosis?

  1. Psoas abscessAnswer
  2. B
    Septic arthritis of the right hip
  3. C
    Acute pyelonephritis
  4. D
    Retrocecal appendicitis
  5. E
    Lumbar radiculopathy

Answer

Psoas abscess
The correct answer is psoas abscess. The patient's clinical presentation of fever, flank/back pain, and a positive psoas sign (pain on passive hip extension) strongly suggests inflammation of the iliopsoas muscle. The fact that the patient prefers to lie with the hip flexed (which relaxes the muscle) and experiences severe pain upon passive extension (which stretches the muscle) is the hallmark physical examination finding for a psoas abscess. The absence of pain with passive internal and external rotation of the flexed hip crucially rules out pathology within the hip joint itself, such as septic arthritis. Furthermore, the patient's recent staphylococcal skin infection provides a classic source for hematogenous spread to the psoas muscle.

Step-by-Step Solution

1
Analyze the patient's vital signs and systemic symptoms.
The patient has a fever and a recent history of a staphylococcal skin infection, indicating an infectious or inflammatory etiology.
To differentiate between infectious/inflammatory causes and purely mechanical or neuropathic causes.
2
Evaluate the key physical examination maneuver (psoas sign).
Pain is elicited on passive right hip extension, but not on internal or external rotation. The patient also prefers to keep the hip flexed to minimize discomfort.
To localize the anatomical source of the pain to the iliopsoas muscle rather than the true hip joint itself.
3
Synthesize the findings to formulate the most likely diagnosis.
The combination of fever, flank/back pain, positive psoas sign, negative hip rotation pain, and recent skin infection classically describes a psoas abscess.
To definitively rule out competing diagnoses like septic arthritis or appendicitis based on the specific exam findings.

Key Concept

The psoas sign (pain on passive hip extension) specifically indicates irritation of the iliopsoas muscle group, which, when combined with fever and recent skin infection, strongly suggests a psoas abscess while normal hip rotation rules out true hip joint pathology.
Estimated Time:1m 30s
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Topics

Physical Examination Findings

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