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Surgical exploration of a painful epitrochlear tumour gave a surprising result.
A woman of 46 noticed a painful mass 4 cm proximal to the medial epicondyle of her right arm; there was no history of trauma or infection. The mass was 3 × 4 × 2 cm when measured clinically and did not involve the skin or underlying musculature. There were no signs of acute infection, lymphangitis or axillary lymphadenopathy and the white blood cell count was normal. Magnetic resonance imaging showed a 6 × 3 cm encapsulated tumour superficial to the fascia (Figure 1) and seeming to involve the epifascial veins. On surgical exploration it proved to be an encapsulated abscess, histologically a vascular inflammatory granuloma. Special staining excluded typical and atypical mycobacteria. Warthin—Starry silver staining revealed aggregates of Gram-negative bacteria characteristic of Bartonella henselae infection (Figure 2). IgG antibodies to Bartonella, measured by an indirect immunofluorescence assay, rose postoperatively from normal (< 1:64) to > 1:512, confirming the diagnosis. The patient's history was re-evaluated. She had recently acquired a one-year-old cat and had noticed a red papule on the skin of her right hand 3½ weeks before the onset of the painful swelling in her elbow which was still present as hyperpigmentation 6 weeks later (Figure 3). She also mentioned an episode with headache and general fatigue without fever, after the appearance of the papule. Her postoperative course was uneventful.
In 1889, Parinaud reported an oculoglandular syndrome of lymphadenopathy and conjunctivitis that is now known as cat-scratch disease (CSD). In 1950, Debré et al.1 described the relationship of adenopathy and house-cat contact. Several genetically related organisms have been implicated in the aetiology. Initially, Afipia felis was believed to be the causal agent. Subsequently, Rochalimaea species were associated with an immune response in patients with CSD. These were renamed as Bartonella in view of extensive 16S rRNA sequence homology with organisms in this genus2. Recently B. henselae has been identified as a major cause for CSD1,2. Cats may infect humans either directly through scratches, bites or licks, or indirectly via an arthropod vector. The cutaneous lesion is typically a round, redbrown, nontender papule that develops one week after contact with a cat, most often a newly acquired kitten. This minor injury often goes unrecognized. In the next 1-2 weeks regional lymph nodes that drain the area gradually enlarge to several centimetres over 2-3 weeks and may stay for another 3 weeks3. Some cases are more severe and last several months; many others go undiagnosed. In about 10% of patients the nodes become infected and suppurate. The lymph nodes most often involved are in the axilla, then the neck and jaw region and the groin3.
Epitrochlear swellings, as seen in our patient, are infrequent. Early in the course of infection lymph nodes show hyperplasia with vascular proliferation. As the infection progresses granulomas appear, and later multiple microabscesses form, fusing to larger abscesses in those nodes that undergo suppuration. Gram-negative, argyrophilic, non-acid-fast, pleomorphic bacilli may be seen in lymph node preparations or may be noted on biopsy of the primary papules. Usually there is a local inflammation of the involved lymph node and not an encapsulated abscess as in our patient. The course of CSD, however, is usually benign and often self-resolving. Malaise, headache, and fever occur in fewer than half the patients3.
In the past, histopathological examination of the involved lymph node specimens was thought to be the most reliable diagnostic test for CSD. Typical findings include stellate caseating granulomas, microabscesses, and lymphoid follicular hyperplasia. Histological examination with Warthin—Starry silver stain or Brown—Hopps tissue Gram stain, with electron microscopy or immunofluorescence, reveals argyrophilic aggregates of bacteria4. However, the tissue stains do not distinguish between species of Bartonella. Although B. henselae organisms can technically be cultured from specimens of tissue or blood, incubation for up to 6 weeks is required1,2,3.
Serological testing for the presence of antibodies to B. henselae is the most widely used test for confirmation of diagnosis. An indirect fluorescent antibody technique is at present the most effective test, with up to 93% sensitivity and 98% specificity in selected populations5; the most sensitive test is a polymerase chain reaction to detect the presence of B. henselae-specific DNA sequences6, but it is not widely available and the quality may vary between laboratories.
Cat-scratch disease is most often seen in children or in association with human immunodeficiency virus infection. It is usually unresponsive to antibiotics, even when the organism is sensitive in vitro. Whereas healthy individuals tend to recover spontaneously, immunocompromised patients are at risk of progressive and fatal infections. The most effective antibiotics seem to be erythromycin, rifampicin, doxycycline and gentamicin2,3,4.