Regional lymphadenopathy with low-grade fever after kitten contact, caused by Bartonella henselae; usually self-limited but can cause systemic disease in immunocompromised hosts.
Also known as: CSD, Bartonella henselae, Bartonellosis, bacillary angiomatosis, Parinaud oculoglandular syndrome
Overview
Subacute regional lymphadenitis caused by Bartonella henselae, a fastidious gram-negative bacillus. Most cases follow a scratch or bite from a young cat (especially kittens with fleas). Immunocompromised patients can develop bacillary angiomatosis, peliosis hepatis, or endocarditis.
Epidemiology
Approximately 12,000 outpatient diagnoses annually in the US (CDC). Highest incidence in children and adolescents in southern states during fall and winter. Kittens harbor higher bacteremia rates than adult cats.
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Question 1DermatologyMedium
A 40-year-old male with a history of IV drug use has multiple crusted nodular skin lesions on his arms, chest, and face over the past 4 months. CD4 is 35. Punch biopsy shows lobular proliferation of small blood vessels with neutrophilic infiltrates and clumps of bacilli on Warthin-Starry silver stain. Which of the following is the most likely diagnosis?
ACat scratch disease
BMycobacterium avium complex infection
CPyogenic granuloma
DBacillary angiomatosis
EKaposi sarcoma
Reveal answer & full explanation
Correct answer: D — Bacillary angiomatosis
ACat scratch disease
BMycobacterium avium complex infection
CPyogenic granuloma
DBacillary angiomatosis✓
EKaposi sarcoma
Why Bacillary angiomatosis is correct
Bacillary angiomatosis (BA) is an opportunistic infection caused by Bartonella henselae (cat scratch — cat flea vector) or B. quintana (body louse — homeless, alcoholic patients)
Occurs almost exclusively in severely immunocompromised patients (CD4 below 100)
Histology: lobular vascular proliferation, neutrophilic infiltrate, clumps of bacilli (Warthin-Starry silver stain); PCR or serology confirms diagnosis
Why the others are wrong
Kaposi sarcoma — violaceous-red vascular lesions can resemble BA clinically but show spindle cells and HHV-8 on histology, not Warthin-Starry bacilli (confused-with vascular tumor)
Cat scratch disease — caused by the same organism (Bartonella henselae) but occurs in immunocompetent hosts with regional lymphadenopathy, not disseminated cutaneous nodules (anchoring on the organism)
Mycobacterium avium complex infection — a disseminated mycobacterial opportunistic infection, not associated with lobular vascular proliferation or Warthin-Starry-positive bacilli (confused-with low-CD4 infection)
Pyogenic granuloma — BA lesions look clinically and histologically like this lobular capillary hemangioma, but pyogenic granuloma is usually a solitary friable papule after minor trauma or in pregnancy and contains no Warthin-Starry-positive bacilli (confused-with lobular capillary hemangioma)
Additional high-yield points
Treatment: azithromycin 500mg daily OR doxycycline 100mg BID x minimum 3 months (longer in immunocompromised — relapse common)
Also involves: liver (peliosis hepatis), spleen, lymph nodes, bone (osteomyelitis), CNS
A 13-year-old boy presents with a tender lump in his right armpit that he first noticed about a week ago, along with low-grade fevers, fatigue, and a mild headache. Roughly 10 days before the lump appeared, his family adopted a young kitten, and he recalls a minor scratch on the back of his right hand that crusted over and healed. On examination there is a 3-cm tender, mildly erythematous lymph node in the right axilla and a small residual papule on the dorsum of the ipsilateral hand. He is otherwise well-appearing, and the remainder of the exam is unremarkable. Which of the following is the most likely diagnosis?
AToxoplasma lymphadenitis
BCat-scratch lymphadenitis
CSporotrichoid lymphangitis
DMycobacterial lymphadenitis
EUlceroglandular tularemia
Reveal answer & full explanation
Correct answer: B — Cat-scratch lymphadenitis
AToxoplasma lymphadenitis
BCat-scratch lymphadenitis✓
CSporotrichoid lymphangitis
DMycobacterial lymphadenitis
EUlceroglandular tularemia
Why Cat-scratch lymphadenitis is correct
The classic triad is present: young cat/kitten exposure, an inoculation lesion (a papule or pustule at the scratch site within 3-10 days), and tender regional lymphadenopathy appearing 1-3 weeks later — most often axillary, cervical, or epitrochlear.
Bartonella henselae is carried by kittens (which have higher bacteremia rates) and spread cat-to-cat by the cat flea; human inoculation through a scratch leads to lymphatic spread and granulomatous lymphadenitis.
Diagnosis is supported by B. henselae IgG/IgM serology (IFA or EIA); most immunocompetent cases are self-limited over 2-4 months, with azithromycin (a 5-day course) reserved for severe or suppurative disease.
Why the others are wrong
Ulceroglandular tularemia: Francisella tularensis follows rabbit or tick exposure and produces a painful skin ulcer with regional nodes, rather than a healed scratch papule after kitten contact.
Mycobacterial lymphadenitis: nontuberculous disease in young children typically causes indurated, often violaceous, relatively nontender nodes without a clear inoculation event, and is diagnosed by AFB stain and culture.
Sporotrichoid lymphangitis: Sporothrix infection follows soil or rose-thorn (gardening) exposure and produces a chain of nodules ascending along the lymphatics, not isolated regional nodal disease after a cat scratch.
Toxoplasma lymphadenitis — kittens can also transmit Toxoplasma gondii, and acute toxoplasmosis causes fever, fatigue, and lymphadenopathy, but it is acquired by ingesting oocysts or undercooked meat, so there is no inoculation papule, and the nodes are typically discrete, minimally tender cervical nodes rather than a tender node draining the scratched hand.
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Bartonella henselae is transmitted from cat to cat by the cat flea (Ctenocephalides felis). Human inoculation through a scratch or bite leads to local replication and lymphatic spread. In immunocompetent hosts, granulomatous inflammation with stellate microabscesses develops. In immunocompromised hosts, vascular proliferation predominates (bacillary angiomatosis).
Clinical presentation
Symptoms
Papule or pustule at inoculation site within 3-10 days, often unnoticed
Tender regional lymphadenopathy 1-3 weeks later — axillary, cervical, or epitrochlear most common
Low-grade fever, fatigue, headache, malaise
Parinaud oculoglandular syndrome: granulomatous conjunctivitis with preauricular lymphadenopathy
Signs / physical exam
Single or matted tender lymph nodes, 1-5 cm
Overlying skin sometimes erythematous; occasional spontaneous suppuration
Hepatosplenic microabscesses on imaging in atypical CSD
In immunocompromised: violaceous vascular papules of bacillary angiomatosis
Classic findings
Adolescent with a kitten and a 3-cm tender axillary node a week after a scratch on the ipsilateral hand.
Differential diagnosis
Mycobacterial lymphadenitis (nontuberculous or M. tuberculosis) — Indurated, often violaceous nodes in children; AFB stain and culture, IGRA
Tularemia (ulceroglandular) — Rabbit or tick exposure; painful ulcer with regional lymphadenopathy; serology
Lymphoma — Painless, progressive, multistation lymphadenopathy with B symptoms; excisional biopsy
Reactive lymphadenitis (viral, dental) — Bilateral, tender, resolves with treatment of source
Sporotrichosis — Gardener with rose-thorn or soil exposure; lymphocutaneous nodular pattern
Plague (bubonic) — Flea bite in endemic Southwest US; rapidly enlarging painful bubo with sepsis
Diagnostic workup
Diagnostic criteria
Cat exposure plus regional lymphadenopathy plus positive Bartonella serology (or PCR or histopathology) supports the diagnosis.
Labs
Bartonella henselae IgG and IgM serology — preferred initial test (IFA or EIA)
Bartonella PCR on lymph node aspirate or tissue if serology equivocal
Histopathology: stellate granulomas with necrosis; Warthin-Starry silver stain shows organisms
CBC and inflammatory markers
Blood cultures if endocarditis suspected (special media required; often culture-negative)
Imaging
Ultrasound of involved nodes for size and suppuration
CT/MRI abdomen for hepatosplenic disease in prolonged fever of unknown origin
Echocardiogram if endocarditis suspected
Treatment
First-line
Most cases in immunocompetent hosts are self-limited over 2-4 months and require no antibiotics
Symptomatic care: NSAIDs, warm compresses
Treat severe disease, large suppurative nodes, or immunocompromise: azithromycin (5-day course is standard) — only RCT-supported regimen for CSD
Doxycycline (cat scratch, Q fever, brucellosis, RMSF) is used for systemic Bartonellosis including retinitis and neuroretinitis
Rifampin added to doxycycline for severe disease such as neuroretinitis; in endocarditis, doxycycline is paired with gentamicin for the first 2 weeks, with rifampin only if gentamicin cannot be used
Bacillary angiomatosis / peliosis hepatis (HIV)
Erythromycin or doxycycline for at least 3 months
Treat HIV and reconstitute immunity
Endocarditis
Doxycycline for 6 weeks plus gentamicin for the first 2 weeks (rifampin replaces gentamicin if it cannot be used)
Valve surgery often required
Neuroretinitis / encephalopathy
Doxycycline + rifampin for 4-6 weeks
Second-line / adjunct
Needle aspiration (not incision and drainage) for tense suppurative nodes — relieves pressure and pain
Avoid I&D, which can produce chronic sinus tracts
Complications
Suppurative lymphadenitis
Parinaud oculoglandular syndrome
Neuroretinitis with macular star
Encephalopathy and seizures
Hepatosplenic microabscesses
Bacillary angiomatosis (HIV/AIDS)
Culture-negative endocarditis
PANCE pearls
Aspirate tense suppurative nodes — do NOT incise and drain (risk of sinus tract).
Azithromycin is the only antibiotic with RCT evidence shortening lymphadenopathy in CSD.
Bacillary angiomatosis in HIV is a great mimic of Kaposi sarcoma — biopsy and Warthin-Starry stain distinguish.
Bartonella is a leading cause of culture-negative endocarditis (along with Coxiella, HACEK, Brucella).
Neuroretinitis with macular star and unilateral vision loss in a young patient = think CSD.
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