Cat-scratch disease lymphadenitis.

Cat-scratch disease is an infectious disease caused primarily by the bacillus Bartonella henselae. Its manifestations can include self-limited regional lymphadenopathy, fever of unknown origin, and visceral organ, neurologic, and ocular involvement. In immunocompromised patients, cat-scratch disease can cause life-threatening systemic disease. This infection generally occurs in young immunocompetent individuals who have been scratched or bitten by a cat; it can also be caused by a flea bite.

In infected patients, a cutaneous lesion develops in 3 to 10 days at the site of primary inoculation. Regional lymphadenopathy, which is the hallmark of cat-scratch disease, appears proximal to the inoculation site after 1 to 3 weeks. Enlarged (5 to 10 cm) nodes are often tender and matted, and they may suppurate (10 to 15% of cases). Erythema of the overlying skin is often present. In the head and neck region, the cervical, supraclavicular, and submandibular lymph nodes are commonly involved. The lymphadenitis may be associated with fever, malaise, headache, and arthralgia. Generalized lymphadenopathy is rare. Cat-scratch lymphadenitis resolves in 1 to 4 months, but in rare cases it has persisted for years.

The diagnosis of cat-scratch disease is primarily a clinical one. Supportive data include serology (immunofluorescence assay and enzyme immunoassay B henselae antibody tests), lymph node biopsy, polymerase chain reaction assay (PCR) and, if possible, culture. Unfortunately, serology assays have poor sensitivity and specificity, PCR is not widely available, and B henselae, a fastidious and slow-growing bacterium, is very difficult to isolate in tissue specimens. Therefore, lymph node biopsy is frequently required to help establish the diagnosis and/or exclude other possible infectious and malignant causes of lymphadenopathy, particularly if symptoms are slow to resolve. Histopathologic findings in involved lymph nodes are nonspecific and vary according to the stage of the disease. The early stage is characterized by follicular lymphoid hyperplasia, followed by microabscess formation and the development of stellate necrotizing granulomas (figure, A). These granulomas characteristically feature central necrosis admixed with clusters of neutrophils and pink fibrin, and they are surrounded by a peripheral rim of epithelioid macrophages and lymphocytes (figure, B). Multinucleated giant cells may be seen.

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The differential diagnosis includes other infections (e.g., staphylococcal and streptococcal infections, mycobacterial and fungal infections, tularemia, lymphogranuloma venereum, brucellosis, and leishmaniasis), Kikuchi disease, Kawasaki disease, and sarcoidosis. Cat-scratch disease bacilli are focal and do not readily stain with a Gram's stain. They may occasionally be demonstrated in formalin-fixed tissue sections by a silver-impregnation stain (Warthin-Starry stain), which may show rods (1.0 to 3.0/am), cocci, or L-shaped forms (figure, C). However, this stain is difficult to perform, and its interpretation is often compromised by a high background of silver precipitate in necrotic material and within macrophages. Recently, a new, antibody-based immunohistochemical stain for B henselae has become commercially available; this stain is much easier to interpret, and it is more sensitive and specific.

Fortunately, most patients with cat-scratch disease experience a gradual resolution of symptoms. For cat-scratch lymphadenitis, a brief course of antibiotics should suffice.

Suggested reading

Cheuk W, Chan AK, Wong MC, Chan JK. Confirmation of diagnosis of cat scratch disease by immunohistochemistry. Am J Surg Pathol 2006;30(2):274-5.

Miller-Catchpole R, Variakojis D, Vardiman JW, et al. Cat scratch disease. Identification of bacteria in seven cases of lymphadenitis. Am J Surg Pathol 1986; 10(4):276-81.

Ridder G J, Boedeker CC, Technau-Ihling K, Sander A. Cat-scratch disease: Otolaryngologic manifestations and management. Otolaryngol Head Neck Surg 2005;132(3):353-8.

Gabriel Caponetti, MD; Liron Pantanowitz, MD

From the Department of Pathology, Baystate Medical Center, Tufts University School of Medicine, Springfield, Mass.