Answer: Prostatic abscess (left lobe) secondary to Staphylococcus aureus
Question 1: The CT scan demonstrates evidence of swelling of the left lobe of the prostate with what appears to be an early ring-enhancing focus, probable abscess.
Question 2: 6/6 blood cultures positive. The Gram stain is consistent with Gram positive cocci in clusters. This is the classic Gram stain for Staphylococcus species. The growth from the culture was identified as methicillin sensitive Staphylococcus aureus (MSSA).
Question 3: The most appropriate antibiotic options include a broad spectrum cephalosporin, such as ceftriaxone or beta-lactam/beta-lactamase inhibitor combination such as piperacillin/tazobactam; a fluoroquinolone 1st or 2nd generation (ciprofloxacin or levofloxacin) may be considered in someone who is significantly allergic to ceftriaxone.
An important step in antibiotic decision-making is examining a patient’s specific history. This includes determining which antibiotics a patient may have been on before this occurrence (often a bacteria that is intrinsically resistant to the antibiotic is selected for) and the prior urine culture results – which bacteria and which antibiotic sensitivity. The clinician is advised to avoid using the same antibiotic that was used before.
In this specific case, the patient had chronic diabetic foot ulcers and had been complaining of a skin eruption in his eyelids. Diabetics are at particularly high risk for Staphylococcus aureus colonization. These complaints and the specific finding of the prostate abscess may have alerted you to an increased likelihood of infection with this bacteria.
A prostatic abscess is a rare disease process. It is generally a result of a more severe acute prostatitis but can similarly arise from a low-grade chronic infection. The bacteria that cause these conditions are also the same ones that are found in urinary tract infections. Bacteria may enter the prostate from reflux back from the urinary tract or epididymal infection; a less common route is through the bloodstream to the prostatic tissues. A chronic foley can be a source of inflammation and risk of bladder colonization and reflux to the prostate.
The most common cause of abscess is E. coli (70% of cases) or other members of the Enterobacteriaceae family. Staphylococcus aureus infection can be seen in patients that have had urinary tract manipulation, such as post-procedurally, or in those with chronic catheters. Enterococcus species is a less common cause; I often see this as a result of post-procedural bleeding, such as prostatectomy or cystoscopy, in a patient that was given cephalosporin antibiotics.
The treatment of a prostatic abscess ranges from conservative antibiotic only measures – in the case of diffuse prostatic disease (more prostatitis) or small abscess – to more drastic measures like a drainage procedure – transurethrally or transrectally.
Returning to Case
This patient had multiple positive blood cultures on multiple days for Staphylococcus aureus. He had a trans-esophageal echocardiograph (TEE) to ensure that there was no heart valve infection (e.g. endocarditis) since Staph is a less common cause of prostate abscess and because he had possibly a renal infarct as well. The constellation of findings suggested that he had hematogenous spread. After he became stable and endocarditis was mostly ruled out and a follow-up CT scan abdomen and pelvis showed improvement, he finished a course of approximately 10 days of IV antibiotics and then was transitioned to doxycycline 100mg twice daily to complete an additional 3 weeks.
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