Case and content by Brandon Fainstad, MD
Edits, updates and graphics by Yilin Zhang, MD
- Evaluate a patient with flank pain
- Recognize CT findings of septic pulmonary emboli
- Recognize the difference between complicated and uncomplicated MRSA infection
- Identify first line therapies for treatment of MRSA bacteremia (optional)
This case walks through the evaluation of a patient with flank pain. Depending on the level of learner, spend as much or as little time working through the differential of his CT findings. There is an optional teaching point at the end about first line therapies for MRSA bacteremia. This teaching point can take between 1 – 10 min depending on the level of detail your learners are interested in. The reference table provided additionally includes common side effects of these antibiotic therapies.
A 60 year old woman presents to the ED with nausea, emesis and L sided flank pain for 18hrs. The pain is constant, improved when leaning forward and aggravated with inspiration. She denies fevers but reports chills and rigors. She denies SOB, productive cough, dysuria, hematuria, diarrhea. She admits to chronic tooth pain, a small draining boil on her R buttock. Her PMH is significant for COPD, depression, hemochromatosis and nephrolithiasis. She only takes NSAIDS and APAP as needed for pain and reports following recommended doses. She was previously homeless but is currently living in the basement where there was recently confirmed mold infection. She moved from the southeast United States a year ago and denies any other domestic or international travel. She smokes tobacco but denies any IV drug use.
T37.1C, HR 110, BP 120/65, SaO2 95% RA, RR 24
GEN: leaning forward in moderate distress
HEENT: red and swollen gingiva w/o palpable fluctuance. Multiple missing teeth
PULM: tachypneic, shallow breathing, no wheezing, CTAB
CV: tachycardic, regular, no murmurs, non-elevated JVD, good distal pulses
GI: soft, non-distended, mild tenderness over LUQ/lower ribs.
Skin: <1 cm boil over R buttock with small amount of sanguinous drainage, no surrounding erythema or induration
GU: no CVA tenderness
What is your differential based on her history and physical?
- Kidney stone
- Pneumonia – community acquired, but also including TB, fungal pneumonia based on her history of homelessness, mold infection and travel
- PUD/ gastritis
BMP notable for BUN 45, Cr 0.7
CBC notable for WBC 25 (88% PMNs)
Venous lactate 1.7
UA: trace ketones, small blood and 1+ hyaline casts
What are your next steps in diagnosis and management?
- Blood cultures x 2
- Sputum culture, Streptococcal urinary antigen, Legionella urinary antigen
- Can consider a respiratory viral panel
- CT KUB – to evaluate for kidney stones
- CT Chest to better evaluate pulmonary infiltrates
- Empiric initiation of antibiotics to at least cover for CAP – e.g., ceftriaxone + azithromycin, levofloxacin, moxifloxacin
What is your interpretation of the CT chest findings in the setting of this patient’s presentation? Reveal to show findings and differential if focusing on “option 2” objectives.
Differential of these findings include:
- Multifocal pneumonia: bacterial vs. fungal vs. viral. Atypical presentation for bacterial CAP.
- Cavitary component and history of homelessness makes TB a possibility as well, though both upper and lower lobe predominance of consolidations is less typical for TB.
- The halo sign is pathognomonic for Aspergillus infections which could be possible given recent mold exposure
- History of travel to SE United States additionally raises possibility of endemic fungal infection
- ANCA positive vasculitis – can present as cavitary lesions
- Septic pulmonary emboli – subpleural or peripheral wedge-shaped opacities are suspicious for pulmonary emboli. Multiple emboli with evidence of central cavitation are suggestive of possible septic emboli. However, no clear exposure or history of infection that would have led to bacteremia. Septic emboli are concerning for endocarditis (specifically R-sided endocarditis).
She was admitted and started on empiric CAP coverage with Ceftriaxone and azithromycin for possible multifocal CAP. She continued to be tachycardic and febrile through this treatment and was broadened to Vancomycin/Zosyn on HD1. Her blood cultures returned positive for GPCs in clusters and was narrowed to Vancomycin. TTE was performed without any evidence of vegetations. Leading suspicion was primary bacteremia and subsequent development of septic pulmonary emboli or multifocal pneumonia complicated by subsequent bacteremia.
What are septic pulmonary emboli (SPE)? (~2-3 min)
Blood clots containing microorganisms embolize to the pulmonary vasculature and result in infarction and subsequent abscess formation. Symptoms can be insidious in onset and nonspecific. Risk factors include IV drug use and indwelling catheters. In Cook, et al (2005), origin of SPE were associated with IVDU, dental abscesses, endocarditis, infected pacemaker leads, and suppurative thrombophlebitis2.
What are typical CT findings of septic pulmonary emboli (SPE)? (~1-2 min)
- Subpleural nodules or wedge-shaped opacities, with or without necrosis/cavities, often with lower lobe predominance.
- “Feeding vessels” – peripheral nodules with a clearly identifiable supply vessel.
Blood cultures cleared within 48 hours on IV Vancomycin but she developed Vancomycin induced acute interstitial nephritis requiring transition to IV linezolid. She was discharged on PO linezolid to complete a 4 week course for complicated MRSA bacteremia with suspected septic pulmonary emboli. Ultimately, the source of bacteremia was thought to be from the small boil on her buttock versus a periodontal infection. She was ultimately treated with 6 weeks of therapy for complicated MRSA bacteremia.
What is complicated versus uncomplicated bacteremia? (~5 min)
All patients with S. aureus bacteremia should be evaluated with either TTE or TEE. Holland, et al (2014) in JAMA recommended TEE for all patients with S. aureus bacteremia that did not have a “low risk” for infective endocarditis. TTE was sufficient for all “low risk” patients that met the following criteria:
- Nosocomial acquisition of bacteremia
- Sterile follow-up blood cultures within 4 days after the initial positive blood culture
- No permanent intracardiac device
- No hemodialysis dependence
- No clinical signs of endocarditis or secondary foci of infection
What are additional antibiotic options for the treatment of MRSA bacteremia? (~1-10 min)
The antibiotic table in the pop-up below serves as a reference. Depending on the interest of your learners and time allowed, you can choose to what level of detail to go through the table.
Vancomycin and daptomycin are first line therapy for MRSA bacteremia. Daptomycin cannot be used in patients with MRSA pneumonia. The use of other agents listed above are supported by limited or poorer quality evidence4.
Detailed table of antibiotics and common side effects used in the treatment of MRSA bacteremia
TAKE HOME POINTS:
- Consider pulmonary and pleural pathology in assessment of flank pain
- Classic radiographic findings of SPE (septic pulmonary emboli) – predominantly lower lobe, subpleural nodular or wedge shaped infiltrates that may develop cavities and adjacent pleural effusions.
- Uncomplicated MRSA infections – without signs of endocarditis, indwelling prostheses, signs of metastatic infection – can be treated with 2 weeks of antibiotic therapy. Complicated infections should be treated with 4-6 weeks of therapy.
- Vancomycin and daptomycin are first line therapies for MRSA bacteremia.
- Lin, M. Y., K. Rezai, and D. N. Schwartz. “Septic Pulmonary Emboli and Bacteremia Associated with Deep Tissue Infections Caused by Community-Acquired Methicillin-Resistant Staphylococcus Aureus.” Journal of Clinical Microbiology 46.4 (2008): 1553-555.
- Cook, Rachel J., Rendell W. Ashton, Gregory L. Aughenbaugh, and Jay H. Ryu. “Septic Pulmonary Embolism.” Chest 128.1 (2005): 162-66.
- Liu, C, et al. 2011. “Clinical Practice Guideline by the Infectious Diseases Society of America for the Treatment of Methicillin-Resistant Staphylococcus aureus Infections in Adults and Children.” Clinical Infectious Diseases. 53(3):e18-e55.
- Holland, TL, et al. 2014. “Clinical Management of Staphylococcus aureus Bacteremia: A Review.” JAMA. 312(2): 1330-1341.
- Weerakkody, Yuranga. “Septic Pulmonary Emboli.” Radiopaedia Blog RSS. Radiopedia.org, 03 June 2016. Web. 15 June 2016.