Infectious Disease · Zoonotic Infections
The facts most likely to be tested
Bartonella henselae is a Gram-negative rod transmitted primarily through cat scratches or bites from infected kittens.
The classic clinical presentation is regional lymphadenopathy that develops 1–3 weeks after a papule or pustule at the inoculation site.
Axillary, cervical, or submandibular lymph nodes are the most commonly involved sites and may become suppurative.
Immunocompromised patients, particularly those with HIV/AIDS, are at risk for bacillary angiomatosis, which presents as vascular, red-purple skin lesions.
Diagnosis is typically established via serology (IgM/IgG titers) or PCR of lymph node aspirate, as the organism is fastidious and difficult to culture.
Azithromycin is the first-line treatment for patients with moderate-to-severe lymphadenopathy to accelerate recovery.
Parinaud oculoglandular syndrome, characterized by unilateral conjunctivitis and ipsilateral preauricular lymphadenopathy, is a rare but classic manifestation of Bartonella infection.
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A 12-year-old boy is brought to the clinic by his mother due to a painful lump in his left armpit. Two weeks ago, he sustained a minor scratch on his left forearm while playing with a new stray kitten. Physical examination reveals a tender, matted, 3-cm left axillary lymph node and a small, healed crusted papule on the left forearm. The patient is afebrile and has no other systemic symptoms.
What is the most likely diagnosis?
Cat scratch disease (Bartonella henselae)
The patient's history of a cat scratch followed by regional lymphadenopathy is the classic presentation of Bartonella henselae infection, as described in Bet 2 and Bet 3.
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Etiology / Epidemiology
Caused by Bartonella henselae; transmitted via cat scratch or bite (especially kittens).
Clinical Manifestations
Regional lymphadenopathy following a papule at the inoculation site; Parinaud oculoglandular syndrome.
Diagnosis
Serology (IFA) is the diagnostic test of choice; biopsy reserved for atypical cases.
Treatment
Self-limiting; Azithromycin is the first-line agent for moderate-to-severe cases.
Prognosis
Generally excellent; encephalopathy or neuroretinitis are rare, severe complications.
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Epidemiology & Etiology
Caused by the gram-negative bacillus Bartonella henselae. Primarily affects children and young adults following contact with kittens (the primary reservoir). Transmission occurs via scratches, bites, or flea vectors.
Pertinent Anatomy
Infection typically involves the draining lymph nodes proximal to the inoculation site. Common sites include the axilla, epitrochlear, cervical, or submandibular regions.
Pathophysiology
The bacteria inoculate the skin, causing a local erythematous papule within 3–10 days. Regional lymphadenopathy develops 1–3 weeks later, characterized by follicular hyperplasia and granulomatous inflammation. In immunocompromised hosts, it may progress to bacillary angiomatosis.
Clinical Manifestations
Patients present with a tender, regional lymphadenopathy that may suppurate. Parinaud oculoglandular syndrome (conjunctivitis with preauricular lymphadenopathy) is a classic presentation. Red flags include high fever, seizures, or altered mental status, suggesting encephalopathy.
Diagnosis
The IFA (Indirect Fluorescent Antibody) test for B. henselae is the gold standard. PCR testing of lymph node aspirate is highly specific but rarely required. Biopsy is indicated only if malignancy is suspected or if nodes fail to resolve.
Treatment
Most cases are self-limiting and require only supportive care (analgesics). Azithromycin is the first-line antibiotic for patients with systemic symptoms or severe lymphadenopathy. Avoid fluoroquinolones in pediatric patients unless benefits outweigh risks.
Prognosis
Prognosis is excellent with full recovery in weeks to months. Rare complications include neuroretinitis, osteomyelitis, and hepatosplenic abscesses, which require prolonged antibiotic therapy.
Differential Diagnosis
Tularemia: history of rabbit exposure
Sporotrichosis: lymphocutaneous spread
Lymphoma: persistent, non-tender, rubbery nodes
Mycobacterial lymphadenitis: chronic, cold abscesses
Cat scratch disease: tender, regional lymphadenopathy