What is the recommended workup for cat scratch disease?

Workup for Cat Scratch Disease

The recommended diagnostic workup for cat scratch disease (CSD) primarily relies on serologic testing for Bartonella henselae, with PCR testing of lymph node tissue offering the highest specificity (100%) when available. 1, 2

Diagnostic Algorithm

1. Clinical and Epidemiological Assessment

• Document history of cat exposure, especially kittens or feral cats 1
• Note presence of cat flea exposure (important vector) 1
• Assess for characteristic lymphadenopathy (most common presentation) 3
• Check for skin lesions at inoculation site
• Evaluate for systemic symptoms (fever, malaise)
• Screen for immunocompromised status (higher risk for severe disease) 1

2. Laboratory Testing

• First-line: Serologic testing

  • IgG antibody titers to B. henselae (titers >1:256 are diagnostic) 3
  • Most accessible and practical initial test

• Second-line: PCR testing

  • Perform on lymph node tissue specimens 1
  • Highest specificity (100%) of all diagnostic methods 2
  • Consider when diagnosis remains uncertain after serology

• Third-line: Culture

  • Low yield from blood, CSF, or lymph node specimens 1
  • Reserve for cases where other methods are inconclusive

3. Additional Testing for Atypical Presentations

• Consider imaging studies when suspecting:
  • Hepatosplenic involvement
  • Neuroretinitis
  • Osteomyelitis
  • CNS involvement (encephalopathy)

Diagnostic Criteria

The diagnosis of CSD is most reliable when at least two of the following criteria are present 2:

• Positive serology for B. henselae
• Positive epidemiological history (cat exposure)
• Characteristic histological findings
• Positive PCR for B. henselae DNA

Important Considerations

• Diagnostic pitfall: Relying solely on culture has poor sensitivity - use serologic testing as primary diagnostic method 1
• Clinical caveat: Consider CSD in any case of unexplained lymphadenopathy, especially with cat exposure history 3
• Special populations: Immunocompromised patients may present with atypical manifestations like bacillary angiomatosis or bacillary peliosis rather than typical lymphadenopathy 4
• Follow-up: Lymphadenopathy may persist for 1-6 months despite appropriate diagnosis and treatment 1

While most cases of CSD are self-limited and resolve without specific treatment, proper diagnosis is important to rule out other causes of lymphadenopathy and to identify patients who might benefit from antimicrobial therapy, particularly immunocompromised individuals or those with severe or disseminated disease 1, 3.