Cat scratch disease. Identification of bacteria in seven cases of lymphadenitis.

A retrospective study of lymph node biopsy specimens from nine patients with the clinical findings and histologic features of cat scratch disease was undertaken to determine whether the recent report by Wear et al. that pleomorphic bacteria are present in the lymph nodes of cat scratch disease could be confirmed. In seven of our nine cases, pleomorphic bacteria were demonstrated with the Warthin-Starry (WS) silver stain. These were gram-negative with the Brown-Hopps tissue Gram stain and were almost at the limit of microscopic resolution. Lymph node specimens from 13 additional patients with nonspecific lymphadenitis who had neither clinical nor histologic findings of cat scratch disease were studied similarly; in none of these were bacteria demonstrated with the WS silver stain. After examining the distribution of the organisms and the related morphologic features in cat scratch disease, we conclude that demonstration of pleomorphic, gram-negative, WS-positive bacteria in the appropriate clinical and histologic setting can firmly establish the diagnosis of cat scratch disease.