What is the diagnosis for multiple abscesses seen on Magnetic Resonance Imaging (MRI) with negative blood culture results?

From the Guidelines

Multiple abscesses seen on MRI with negative blood cultures should be treated with empiric broad-spectrum antibiotic therapy, such as vancomycin plus ceftriaxone or piperacillin-tazobactam, while pursuing further diagnostic testing, including surgical drainage for accessible abscesses larger than 1 cm. The presence of multiple abscesses on MRI suggests a localized infection that may not have spread to the bloodstream, or it could be caused by organisms that are difficult to culture 1. The negative blood cultures may result from prior antibiotic use, fastidious organisms requiring special culture techniques, or because the infection is well-contained within the abscess 1.

Diagnostic Approach

The diagnostic approach should include:

• Repeat blood cultures to rule out bacteremia
• Aspiration of the abscess under imaging guidance for culture to identify the causative organism
• Serological tests for specific pathogens, such as Bartonella species or Coxiella burnetii
• Molecular diagnostic techniques like PCR to detect DNA in blood specimens or tissue

Treatment Approach

The treatment approach should include:

• Empiric broad-spectrum antibiotic therapy, such as vancomycin (15-20 mg/kg IV every 8-12 hours) plus either ceftriaxone (2g IV daily) or piperacillin-tazobactam (4.5g IV every 6-8 hours)
• Surgical drainage for accessible abscesses larger than 1 cm, as antibiotics alone may not penetrate these collections effectively
• Treatment duration typically ranges from 2-6 weeks depending on the location, causative organism, and clinical response, with regular imaging follow-up to assess resolution 1.

Key Considerations

Key considerations in the management of multiple abscesses with negative blood cultures include:

• Consultation with an infectious diseases expert to optimize the chance of identification of the causative microorganism
• Molecular techniques to identify 16S ribosomal RNA or DNA from tissue or PCR to detect DNA in blood specimens may be useful in identifying the causative organism 1
• Serological methods are often used to diagnose specific pathogens, such as Bartonella species or Coxiella burnetii 1.

From the Research

Multiple Abscesses with Negative Blood Culture

• The presence of multiple abscesses on MRI with negative blood culture can be a challenging diagnosis, as it may indicate a complex infection or an underlying condition that requires further investigation 2.
• In such cases, it is essential to consider various diagnostic conditions, including community-acquired or family-transmitted infections, acquired or innate immunodeficiencies, chronic dermatoses, or other systemic diseases 2.
• The choice of empiric antibiotic therapy is crucial, and it should be based on the likely etiologies and anticipated resistance patterns 3.
• Current diagnostic and treatment guidelines suggest that all seriously ill patients in whom infection is suspected undergo a comprehensive work-up, including blood, urine, and sputum cultures, to confirm the etiology prior to initiation of antibiotic therapy 3.

Antibiotic Therapy for Abscesses

• Antibiotic penetration into abscess fluid is limited and highly dependent on the degree of abscess maturation 4.
• The efficacy of antibiotics in pus may be hampered by various factors, such as low pH, protein binding, and degradation by bacterial enzymes 4.
• Initial empiric broad-spectrum antibiotic therapy is necessary for the treatment of patients with serious infections, following a thorough evaluation of possible sources, including culture and susceptibility testing 3.
• The use of novel therapeutic agents, such as daptomycin, linezolid, and tigecycline, may be considered for the treatment of complex infections, including those caused by multi-drug-resistant Gram-negative bacteria 3, 5.

Empirical Antibiotic Therapy

• Empirical antibiotic therapy should be tailored based on the patient's initial response, and susceptibility test results should be available to guide therapy 3.
• The use of ceftriaxone and metronidazole as empirical therapy may be appropriate for certain types of infections, such as perforated appendicitis and cholecystitis, but broader spectrum antimicrobial therapy may be necessary for other cases, such as perforated bowel and sigmoid diverticulitis 6.
• Novel agents, such as those active against Gram-negative bacteria with difficult-to-treat resistance, should be used in line with antimicrobial stewardship principles, aimed at reducing selective pressure for antimicrobial resistance 5.