Cat Scratch Disease

1. Epidemiology
   1. Most common in young patients
   2. Age under 21 years in 80% of cases
   3. Most common in late summer and fall in the northern United States
   4. Incidence: 22,000 new cases per year in the United States
2. Pathophysiology
   1. Infection by Bartonella henselae
      1. Previously known as Rochalimaea henselae
      2. Gram Negative Rod
   2. Organism transmitted between cats by the cat flea, Ctenocephalides felis
      1. Can also directly infect humans via its bite
      2. Ticks may also act as vectors
   3. Cats transmit the Bartonella henselae to humans
      1. Cats transit the infection via biting or clawing humans
      2. B. henselae lives in feline erythrocytes, and contaminates their Saliva
      3. Present in 50% of cats (who are asymptomatic)
3. Symptoms
   1. Myalgias
   2. Arthralgias
   3. Malaise
   4. Anorexia
   5. Low-grade fever (uncommon)
4. Signs
   1. Dermatitis at cat scratch or bite
      1. Local Papule, Pustule or Vesicle overlying initial scratch or bite site
   2. Persistent painful regional, ipsilateral Lymphadenopathy (85-90% of cases)
      1. Onset 1-2 weeks after the initial rash, and may persist for months
      2. Overlying reddened skin
      3. Lymph nodes fluctuant but sterile
      4. Distribution: Upper extremities, Neck, Jaw and Groin are the most commonly involved sites
5. Differential Diagnosis
   1. See Regional Lymphadenopathy
   2. Mycobacterium infection and neoplasm can co-occur with Cat Scratch Disease
      1. Therefore, follow the Lymphadenopathy until resolution
6. Complications (2%)
   1. Neurologic involvement
      1. Meningoencephalitis
      2. Encephalopathy
         1. Presents as severe Headache and acute confusion at 1-6 weeks after Regional Lymphadenopathy develops
   2. Ocular involvement
      1. Parinaud Oculoglandular Syndrome
         1. Granulomatous Conjunctivitis with periauricular adenopathy
      2. Neuroretinitis
         1. Acute unilateral visual field loss secondary to Optic Nerve edema with macular exudates (star-shaped)
   3. Bacillary Angiomatosis (immunosuppressed patients)
      1. Bacillary peliosis can involve the liver and Spleen
      2. Bacillary Angiomatosis can involve bone and skin (red to purple Papules)
   4. Endocarditis
7. Lab
   1. Anti-Bartonella henslae serology (preferred)
      1. Indirect fluorescent or enzyme-linked immunosorbent assay
      2. IgG titers over 1:256 suggests active or recent infection
         1. Titers 1:64 to 1:256 should be rechecked in 10-14 days
      3. IgM is more specific for acute infection, but poor Test Sensitivity due to very brief IgM production
   2. Excisional Biopsy
      1. Indicated if diagnosis is unclear or if Lymphadenopathy persists
      2. General Findings
         1. Lymphoid Hyperplasia
         2. Stellate granulomas
         3. Small curved, aerobic, pleomorphic intracellular Rods
         4. Warthin-Starry silver impregnation stain
      3. Findings in Bacillary Angiomatosis
         1. Lobular proliferation of small vessels
         2. Bacilli in adjacent connective tissue
   3. Historical tests
      1. Skin test with antigen (Hanger-Rose skin test)
   4. Not recommended:
      1. Wound culture
      2. Bartonella PCR (lower sensitivity than serology, but very specific)
      3. Incision and Drainage
8. Management : Cat-Scratch Disease
   1. Self limited infection with Lymphadenopathy resolving within 8 weeks and no other sequelae
      1. Antibiotics not required
   2. Indications for antibiotic therapy
      1. Extra-dermatologic involvement (liver, Spleen, CNA)
      2. Moderate involvement
   3. Antibiotics
      1. Azithromycin for 5 days (Z-Pack)
         1. Lymphadenopathy resolves more readily on Azithromycin
         2. Bass (1998) Pediatr Infect Dis J 17(6): 447-52
      2. Rifampin
      3. Ciprofloxacin
      4. Trimethoprim-Sulfamethoxazole (Bactrim, Septra)
      5. Gentamicin
9. Management:
   1. Bacillary Angiomatosis or bacillary peliosis
      1. Duration: 3-4 months
      2. Antibiotics: Erythromycin, Doxycycline
   2. Neurologic sequelae
      1. Duration: 4-6 weeks
      2. Antibiotics: Rifampin with either Erythromycin or Doxycycline
10. Course
    1. Spontaneous resolution common
11. References
    1. Klotz (2011) Am Fam Physician 83(2): 152-5
    2. Massei (2005) Infect Dis Clin North Am 19(3): 691-711