Cat Scratch Disease (cont.)
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Exams and Tests
Most cases of CSD are diagnosed by the patient's clinical presentation and history. If the patient has a history of cat scratches (or superficial bites or a cat licking their face or cuts) and then develops papules or pustules, many physicians consider these findings enough to diagnose CSD. If the patient also develops swollen lymph nodes and fever, these findings reinforce the clinical diagnosis of CSD. Microscopic examination with special stains of biopsied tissue (lymph nodes) may show small curved Gram-negative rods, but the staining methods do not yield a definitive diagnosis of CSD. Laboratory tests are also available; indirect fluorescent antibody and rising immunoglobulin titers may provide additional evidence for infection with Bartonella henselae but are not frequently done. A polymerase chain reaction (PCR) test to detect the genetic material of the bacteria that shows good sensitivity and specificity for Bartonella can be done on the patient's tissue, but the test is not widely available.
Although laboratory tests are infrequently used, their availability is important because about 10% of patients with CSD do not recall or state an association with cats or kittens. This lack of clinical history makes the diagnosis of CSD difficult. These tests can help physicians differentiate CSD from other diseases caused by organisms similar to Bartonella (for example, Anaplasma phagocytophilum and Acinetobacter baumanni, which are both small pleomorphic Gram-negative bacilli) or from other diseases that have some similar symptoms (for example, swollen lymph nodes in lymphoma or in Actinobacillosis).
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