WBR0876
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| Author | [[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]] |
|---|---|
| Exam Type | USMLE Step 1 |
| Main Category | Microbiology |
| Sub Category | Infectious Disease |
| Prompt | A 75-year-old man with history of severe emphysema maintained on home oxygen is admitted to the intensive care unit for desaturation on 100% FiO2. On admission, his heart rate is 133/min, blood pressure is 80/53 mmHg, and temperature is 39.1 °C (102.4 °F). Despite efforts, the patient dies shortly after admission. Post-mortem examination reveals several black necrotic lesions with a surrounding erythematous edge most prominent on the lower extremities. Blood cultures withdrawn on admission, reveal growth of rod shaped gram-negative organisms. What is the most likely organism involved in the patient's presentation? |
| Answer A | Escherichia coli |
| Answer A Explanation | Escherichia coli sepsis is not classically associated with ecthyema gangrenosum although a few cases have been reported. |
| Answer B | Klebsiella pneumoniae |
| Answer B Explanation | Klebsiella pneumoniae sepsis is not classically associated with ecthyema gangrenosum although a few cases have been reported. |
| Answer C | Citrobacter freundii |
| Answer C Explanation | Citrobacter freundii sepsis is not associated with ecthyema gangrenosum. |
| Answer D | Pseudomonas aeruginosa |
| Answer D Explanation | Pseudomonas aeruginosa sepsis is the classical cause for ecthyema gangrenosum. |
| Answer E | Proteus mirabilis |
| Answer E Explanation | Proteus mirabilis sepsis is not associated with ecthyema gangrenosum. |
| Right Answer | D |
| Explanation | Ecthyema gangrenosum is a skin manifestation of Pseudomonas aeruginosa sepsis characterized by a round or oval lesion of varying size, with a necrotic center and a halo of erythema. The necrotic center represents an area of infarction due to blood vessel infection and invasion. Although ecthyema can be seen in patients with other gram negative bacteremias, it is classically associated with Pseudomonas aeruginosa and linked to exotoxin A producing strains. It is a rare finding but occurs more in patients with severe immunosuppression or neutropenia and neonates. Educational Objective: Ecthyema gangrenosum is a skin manifestation of Pseudomonas aeruginosa sepsis characterized by a lesion of varying size, with a nectoric center and a halo of erythema. |
| Approved | Yes |
| Keyword | Pseudomonas aeruginosa, Ecthyema gangrenosum, Sepsis |
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