Radiological Case of the Month

Figure 1. A 2-cm lymph node in the right axilla (arrow).

Figure 2. Lytic lesion of the left first rib (arrow).

Figure 3. Nodular lesion in the left upper lobe (arrow).

The lymph node biopsy revealed granulomatous inflammation with fungal hyphae; a diagnosis of Bartonella henselae infection was confirmed using polymerase chain reaction on the lymph node specimen.

Cat-scratch disease (CSD) is a relatively common bacterial infection occurring all over the world. In the United States, it is estimated that 22,000 to 24,000 cases occur each year with 2000 patients requiring hospitalization.^1,2 Although CSD is considered a childhood disease, 20% of the cases occur in people aged 20 years or older.³ Sixty percent of cases occur in men; the preponderance of patients are white.^3,4 Cat-scratch disease occurs most frequently in the fall and winter.³

Wear et al⁵ were the first to definitively identify a bacterium as the etiologic agent in CSD. This organism was designated Afipia felis. More recently, other studies indicated Bartonella (formerly Rochalimaea henselae, a fastidious, slow-growing, gram-negative organism) as the major causative agent of CSD.^6,7

Cat-scratch disease can affect all organ systems and cause a variety of clinical manifestations. Lymphadenopathy is the most common presentation, occurring in more than 80% of cases.³ Axillary lymph nodes, followed by cervical and mandibular nodes, are most commonly involved. Mild systemic symptoms may also be present. Additionally, 5% to 20% of patients are seen with more atypical presentations.³ These include Parinaud oculoglandular syndrome, encephalopathy/encephalitis, radiculopathy, rashes, pneumonitis, and osteolytic lesions.

Pulmonary involvement is a rare complication of CSD occurring in less than 1% of cases.⁸ The severity of the disease process varies from mild to severe and some patients require assisted ventilation. Abbasi⁹ reported 4 cases, all of which had pleural involvement as well as parenchymal disease. Typically, exudative pleural fluid is present, which may require drainage. Complete recovery is usual.

Osteomyelitis is also seen in less than 1% of cases of CSD.^10,11 It has been reported that direct extension from an adjacent involved lymph node is the causative mechanism, but hematogenous spread is also likely.¹⁰ Any region of the skeleton may be affected. Bone biopsy will show granulomatous inflammation with central necrosis.¹² Imaging studies such as computed tomography, magnetic resonance imaging, or bone scans are helpful to identify the lesion but are not specific.¹³

Historically, diagnosis was based on meeting 3 of 4 criteria: history of an intimate exposure to a healthy cat (especially a kitten) and an inoculation site, regional adenopathy with sterile pus, a positive cat-scratch test> result, and a lymph node biopsy showing granulomas and abcessess. Currently, a more definitive diagnosis ispossible using enzyme-linked immunosorbent assay for IgM and IgG and indirect immunofluorescent assay, but sensitivity and specitivity varies among laboratories. The identification of B henselae as the most common causative agent for CSD makes the role of culture more promising.² Polymerase chain reaction assay is more sensitive than culture and establishes the diagnosis very early.^4,14

Most people with CSD require no therapy. The lymphadenopathy associated with this infection spontaneously resolves in 2 to 4 months. Needle aspiration of the suppurated lymph node may be necessary to relieve pain, but it rarely needs to be repeated.

Antimicrobial therapy is controverial. Most studies have not demonstrated any significant alteration in the course of the disease when it is used. However, in patients who are severely ill or immunosuppressed, rifampin, trimethoprim-sulfamethoxazole, ciprofloxacin, and parenteral gentamicin sulfate have been shown to be effective in some cases.^2,15,16 In patients with bacillary angiomatosis, erythromycin and doxycycline are considered the first and second line of treatment, respectively.²

Control of the disease is directed at prevention. Cats, particularly kittens, are the major source of infection from B henselae. Avoidance of bites and scratches from these animals or prompt cleaning if they occur is imperative.

Accepted March 10, 1998.

Reprints: Mirzada Kurbasic, MD, Department of Pediatrics, University of Louisville School of Medicine, Louisville, KY 40292.