A 55-year-old man comes to the emergency department with fever and chills. He has a history of acute myeloid leukemia for which he is receiving chemotherapy. His temperature is 38.3 C (101 F), blood pressure is 90/50 mm Hg, pulse is 124/min, and respirations are 22/min. Physical examination is notable for multiple skin patches with necrotic centers and occasional ulcerations, as shown in the image below. Laboratory results are as follows: Blood cultures are drawn. Which of the following organisms is most likely responsible for this patient's symptoms?

Question

A 55-year-old man comes to the emergency department with fever and chills.  He has a history of acute myeloid leukemia for which he is receiving chemotherapy.  His temperature is 38.3 C (101 F), blood pressure is 90/50 mm Hg, pulse is 124/min, and respirations are 22/min.  Physical examination is notable for multiple skin patches with necrotic centers and occasional ulcerations, as shown in the image below.  Laboratory results are as follows:  Blood cultures are drawn.  Which of the following organisms is most likely responsible for this patient's symptoms?

Quizplus · Accepted Answer

This immunosuppressed patient has febrile neutropenia (absolute neutrophil count [ANC] of 0.60 × 800 = 480/mm³, likely in the setting of chemotherapy) and sepsis. With neutropenia (typically ANC <500/mm³), there is increased susceptibility to infections with gram-negative organisms such as Pseudomonas aeruginosa. The dermatologic lesions in this patient are consistent with ecthyma gangrenosum (EG), which is strongly associated with P aeruginosa bacteremia. Perivascular bacterial invasion of arteries and veins in the dermis and subcutaneous tissue, with subsequent release of exotoxins destructive to human tissue, leads to characteristic skin patches exhibiting necrosis and ulceration as a result of insufficient blood flow. P aeruginosa virulence factors that may contribute to EG include exotoxin A (protein synthesis inhibition), elastase (degrades elastin - important for blood vessel destruction), phospholipase C (degrades cellular membranes), and pyocyanin (generates reactive oxygen species). Although gram-negative sepsis is sometimes associated with disseminated intravascular coagulation (DIC) and resultant purpuric skin lesions, DIC is unlikely given the normal platelet count and coagulation times (prothrombin and activated thromboplastin times). (Choice A) Escherichia coli is not associated with EG. E coli is the most common cause of gram-negative sepsis, usually following urinary tract infections. Thrombotic thrombocytopenic purpura-hemolytic uremic syndrome, sometimes seen with Shiga toxin-producing E coli, is classically associated with renal failure and thrombocytopenia (not seen in this patient). (Choices B and E) Streptococcus pneumoniae and Haemophilus influenza are typically associated with respiratory infections and can be isolated from blood, cerebrospinal fluid, or respiratory sources. They are not associated with EG. (Choice C) Klebsiella pneumoniae infection is most commonly associated with necrotizing pneumonia in elderly or immunocompromised patients. (Choice F) Streptococcus pyogenes (Group A Streptococcus) frequently causes cutaneous infections (eg, impetigo, erysipelas) and necrotizing fasciitis, a rapidly progressive deep tissue infection that spreads contiguously along the muscle fascia. Necrotizing fasciitis initially appears as a single site of infection with erythema, edema, warmth, and pain out of proportion to physical findings. This progresses to purpuric discoloration, bullae formation, and sensory loss due to tissue necrosis. Educational objective: Ecthyma gangrenosum is a cutaneous necrotic disease with a strong association with Pseudomonas aeruginosa bacteremia. It occurs from perivascular invasion and release of tissue-destructive exotoxins, causing vascular destruction and insufficient blood flow to patches of skin that become edematous and subsequently necrose. Pseudomonas infections are common in patients who are neutropenic, are hospitalized, have burns, or have indwelling catheters. __________ References: Ecthyma gangrenosum: a manifestation of Pseudomonas sepsis in three paediatric patients. (http://www.ncbi.nlm.nih.gov/pubmed/17139406)

A 55-Year-Old Man Comes to the Emergency Department with Fever