What are the typical presentation and treatment of cat scratch disease?

Cat Scratch Disease: Presentation and Treatment

Cat scratch disease is typically characterized by regional lymphadenopathy following a cat scratch or bite, and while most cases are self-limiting, treatment with azithromycin is recommended for moderate to severe cases. 1

Clinical Presentation

Typical Manifestations

• Primary lesion: Papule or pustule at the site of inoculation (cat scratch or bite) that appears 3-10 days after exposure
• Regional lymphadenopathy: Most common manifestation, typically developing 1-2 weeks after inoculation
  • Most frequently affects axillary (61.5%), cervical, and submandibular lymph nodes 2
  • Lymph nodes become tender, enlarged, and may develop suppurative components
  • Lymphadenopathy may persist for 1-6 months despite treatment 1
• Systemic symptoms: Fever, malaise, fatigue, headache, and anorexia 3

Atypical Manifestations

• Parinaud oculoglandular syndrome (conjunctival granuloma with preauricular lymphadenopathy)
• Neuroretinitis and stellate neuroretinitis
• Encephalopathy (rare but serious complication)
• Persistent fever without localizing signs
• Hepatosplenic infection
• Osteomyelitis
• Endocarditis 4

Risk Factors

• Contact with cats, especially kittens and feral cats 5
• Cat flea infestation (fleas are vectors for Bartonella henselae among cats) 5
• Immunocompromised status (risk for more severe disease) 5, 1

Diagnosis

Diagnostic Approach

1. History: Recent cat exposure (present in ~70% of cases) 2
2. Physical examination: Regional lymphadenopathy and possible inoculation site
3. Serologic testing: Primary diagnostic method 5
4. Imaging:
   • Ultrasound shows conglomerated, lobulated lymph nodes with cortical thickening
   • Approximately one-third of cases show cystic suppurative components 2
5. Culture: Low yield from blood, CSF, or lymph node specimens 5
6. PCR: Can be performed on lymph node tissue specimens 5

Treatment

Immunocompetent Patients

• Mild disease: Often self-limiting and may not require antibiotics 4
• Moderate to severe disease: Azithromycin is the first-line treatment
  • Dosage: 500 mg on day 1 followed by 250 mg for 4 additional days (for patients ≥45.5 kg)
  • 10 mg/kg on day 1 and 5 mg/kg for 4 more days (for patients <45.5 kg) 1
  • Azithromycin has been shown to reduce lymph node size more rapidly than placebo 1, 4

Alternative Antibiotics (based on clinical response)

• Doxycycline: 100 mg twice daily
• Rifampin: Has shown 87% efficacy in some studies 3
• Ciprofloxacin: Has shown 84% efficacy 3
• Trimethoprim-sulfamethoxazole: 58% efficacy 3

Special Populations

1. Immunocompromised patients:

   • Require longer treatment duration (2 weeks to 2 months)
   • Options include erythromycin 500 mg four times daily or doxycycline 100 mg twice daily 1
   • At risk for developing bacillary angiomatosis and bacillary peliosis hepatis 5

2. Pregnant patients:

   • Erythromycin is preferred
   • Tetracyclines should be avoided 1

3. Patients with severe infection:

   • May require hospitalization and IV antibiotics
   • Gentamicin has shown 73% efficacy for severe cases 3

Prevention

• Implement flea control for cats
• Avoid rough play with cats
• Keep cats' nails trimmed
• Supervise children's interactions with cats
• When acquiring a cat, choose an animal older than 1 year and in good health 1

Follow-up

• Clinical reassessment within 24-48 hours for patients with worsening lymphangitis and edema
• Follow-up appointment in 1-2 weeks to assess symptom resolution
• Patients should be informed that lymphadenopathy may persist for 1-6 months despite appropriate treatment 1

Complications and Pitfalls

• Failure to consider cat scratch disease in patients with unexplained lymphadenopathy
• Misdiagnosis as malignancy or tuberculosis
• Delayed treatment of severe manifestations in immunocompromised patients
• Inadequate duration of therapy for immunocompromised patients
• Not recognizing atypical presentations such as neuroretinitis or encephalopathy