What is the recommended treatment for a patient with multiple splenic abscesses and a history of exposure to multiple cats, considering potential infectious causes such as Bartonella henselae?

Treatment of Multiple Splenic Abscesses in a Cat-Exposed Patient

For a patient with multiple splenic abscesses and cat exposure, initiate azithromycin 500 mg on day 1 followed by 250 mg daily for 4 days (for patients >45 kg) as first-line therapy, with doxycycline 100 mg twice daily for at least 3 months reserved for treatment failure or severe disease. 1

Primary Infectious Etiology

• Bartonella henselae is the most likely causative organism given the history of multiple cat exposure and splenic abscess formation 2, 3, 4
• Multiple splenic abscesses represent an atypical, severe manifestation of cat scratch disease that occurs in <2% of cases 1
• The diagnosis should be confirmed with B. henselae serology, though antibodies may not be detectable until 6 weeks after acute infection 1
• Consider PCR or Warthin-Starry silver stain of tissue if biopsy is performed, as these can provide definitive diagnosis when serology is negative or equivocal 1

Initial Treatment Algorithm

First-Line Therapy

• Start azithromycin immediately while awaiting serologic confirmation: 500 mg on day 1, then 250 mg daily for 4 additional days for standard cat scratch disease 1
• However, for hepatosplenic involvement with multiple abscesses, prolonged therapy beyond the standard 5-day course is necessary 3, 4
• The CDC recommends extending treatment to at least 3 months for severe systemic bartonellosis 5

Treatment Escalation for Severe Disease

• If no clinical improvement within 1-2 weeks, switch to doxycycline 100 mg twice daily with or without rifampin 5, 1
• Doxycycline is the CDC's first-line agent for severe bartonellosis and should be continued for at least 3 months 5
• Rifampin (20 mg/kg, maximum 600 mg/day) can be added to doxycycline for more extensive disease 5

Alternative Regimens

• Erythromycin 500 mg four times daily is an alternative if azithromycin or doxycycline are contraindicated 1
• For severe cases with rapid deterioration, gentamicin has shown 73% efficacy with response within 48 hours 1

Critical Management Considerations

Antibiotics to Absolutely Avoid

• Never use penicillins or first-generation cephalosporins—they have no in vivo activity against Bartonella 5, 1, 6
• Avoid quinolones and TMP-SMX as monotherapy due to variable activity and inconsistent clinical response 5, 1

Immunocompromised Patients

• If the patient is immunocompromised (HIV with CD4+ <100 cells/µL, on chemotherapy, or other immunosuppression), treat more aggressively with doxycycline or erythromycin for >3 months 1, 7
• Up to 25% of HIV patients with advanced disease may never develop antibodies despite active infection 1
• Consider bacillary angiomatosis, peliosis hepatis, or CNS involvement in immunocompromised hosts 1, 7
• Long-term suppression is recommended until immune reconstitution occurs 5, 1

Surgical Intervention

• Medical management should be attempted first, as most cases respond to prolonged antibiotic therapy 3, 4
• Splenectomy is reserved for cases that fail medical management or develop life-threatening complications 2
• One case series showed successful treatment with antibiotics alone, avoiding invasive procedures 3

Monitoring and Follow-Up

• Assess clinical response within 1-2 weeks: expect fever resolution and symptomatic improvement 5
• Repeat imaging (CT or ultrasound) at 4-6 weeks to document abscess resolution 3, 4
• If no improvement occurs, consider alternative diagnoses or escalate to combination therapy with doxycycline plus rifampin 5
• Monitor for pill-associated esophagitis if using doxycycline—instruct patients to take with adequate fluid and avoid bedtime dosing 5

Common Diagnostic Pitfalls

• Do not wait for serology to initiate treatment—start empiric therapy based on clinical suspicion and cat exposure history 1
• Serology performed <6 weeks after symptom onset may yield false-negative results 1
• Do not test the cats for Bartonella—this provides no diagnostic or management benefit 1
• Consider Bartonella in any patient with fever of unknown origin and cat exposure, even without obvious lymphadenopathy 1, 2
• Multiple renal lesions may also be present on imaging and support the diagnosis 4

Special Population Adjustments

Pregnant Women

• Use erythromycin exclusively—doxycycline is absolutely contraindicated in pregnancy 1
• Erythromycin 500 mg four times daily for at least 3 months is the recommended regimen 1

Pediatric Patients

• Weight-based azithromycin dosing: 10 mg/kg on day 1, then 5 mg/kg for 4 days 5, 1
• Doxycycline 2-4 mg/kg/day (maximum 100-200 mg/day) for severe disease 5
• Fluoroquinolones should be avoided in children unless no alternatives exist 1