Can a lymph node biopsy diagnose Cat Scratch Fever (Cat Scratch Disease, CSD), caused by Bartonella henselae, which is typically transmitted through a cat scratch?

From the Guidelines

A lymph node biopsy can be used to diagnose cat scratch fever, particularly in cases where the diagnosis is unclear or symptoms persist despite treatment. When a patient presents with persistent lymphadenopathy and a history of cat exposure, a lymph node biopsy may be performed to confirm the diagnosis, as it can provide characteristic histopathological findings such as granulomatous inflammation and the presence of Bartonella henselae bacteria 1. The biopsy can be useful in identifying the causative agent of the infection, which is essential for guiding treatment. According to the 2014 practice guidelines for the diagnosis and management of skin and soft tissue infections by the Infectious Diseases Society of America, a positive Warthin-Starry silver stain of infected lymph node tissue is useful to confirm the diagnosis, although it cannot differentiate species of Bartonella 1.

Some key points to consider when diagnosing cat scratch fever include:

• The disease course varies, but lymphadenopathy generally resolves within 1–6 months 1
• In about 10% of cases, the nodes suppurate 1
• Extranodal disease (eg, central nervous system, liver, spleen, bone, and lung) develops in ≤2% of cases 1
• Bartonella henselae causes most cases of cat scratch disease in immunocompetent hosts 1

Treatment of cat scratch disease with antimicrobial agents, such as azithromycin, has had variable results, but a single, double-blind placebo-controlled study found that azithromycin treatment resulted in significant regression of lymph node size 1. The recommended dose of azithromycin for patients weighing ≥45.5 kg is 500 mg on day 1, then 250 mg once daily for 4 additional days; for those weighing <45.5 kg, the dose is 10 mg/kg orally on day 1, then 5 mg/kg on days 2–5 1. However, it's essential to weigh the benefits and risks of the biopsy procedure, which carries small risks of bleeding, infection, and scarring at the biopsy site.

From the Research

Lymph Node Biopsy in Cat Scratch Fever

• Lymph node biopsy can be used to diagnose cat scratch disease (CSD) 2, 3, 4, 5
• The biopsy can help visualize the organisms causing the disease, such as Bartonella henselae, using Warthin-Starry silver impregnation staining 2
• However, the sensitivity of PCR assays on lymph node biopsy specimens can be lower compared to other clinical specimens, such as pus aspirates or primary lesions 5
• The sensitivity of PCR on lymph node biopsy specimens was found to be 73% in one study, with a negative predictive value of 72% 5

Diagnosis of Cat Scratch Disease

• Cat scratch disease is typically diagnosed by obtaining a history of exposure to cats and a serologic test with high titers of immunoglobulin G antibody to B. henselae 6
• Lymph node biopsy can be used to support the diagnosis, especially in cases where the diagnosis is uncertain or the patient has atypical symptoms 2, 3
• Other diagnostic methods, such as ultrasonography and PCR assays, can also be used to diagnose CSD 3, 5

Treatment of Cat Scratch Disease

• Most cases of cat scratch disease are self-limited and do not require antibiotic treatment 6
• However, in some cases, antibiotic treatment may be necessary, and azithromycin has been shown to be effective in speeding recovery 6, 3
• Lymphadenectomy may also be necessary in some cases, especially if the patient has a large or painful lymph node mass 3