Ocular manifestations of cat-scratch disease: role of MR imaging.

In this issue of the AJNR, Schmalfuss et al report the MR imaging features of optic neuropathy due to cat scratch disease (CSD). MR imaging in five of nine patients with CSD demonstrated abnormal contrast enhancement of the optic nerve disk and a short segment of optic nerve just behind the globe. Attempting to understand the MR imaging findings in CSD requires insight into the pathogenesis of CSD and its ocular manifestations, particularly CSD neuroretinitis. CSD is almost always a self-limited systemic illness, and usually presents as a benign tender lymphadenitis involving the lymph nodes draining dermal or conjunctival sites of inoculation. The disease was first reported in 1950 by Debré et al (1). Since then, despite numerous reports on CSD, and despite clinical, epidemiologic, serologic, and pathologic studies that have suggested an infectious pathogen, the causative agent of the CSD had eluded detection until 1983, when Wear et al (2) at the Armed Forces Institute of Pathology (AFIP) identified a small pleomorphic Gram-negative bacillus from lymph nodes of seven of eight patients who were positive for CSD. The bacilli were clearly seen with the Warthin-Starry (WS) silver impregnation stain. The bacilli were found to be very small at the limit of the resolving power of the light microscope, although the WS silver impregnation stain resulted in coating the organisms, making them appear larger and easier to see (2). The bacilli were shortly identified in skin at the primary inoculation site (3) and in the conjunctiva of patients with Parinaud oculoglandular syndrome (4). Initial attempts to isolate and culture this pleomorphic Gram-negative bacilli were unsuccessful until 1988, when English et al (5) at AFIP were successful in isolation and cultivation of a pleomorphic Gram-negative bacillus from lymph nodes of 10 patients with clinically or histopathologically proven CSD. This causative agent became known as the “cat-scratch disease bacillus” and when Brenner et al (6) described, the new genus Afipia, the CSD bacillus was given the name Afipia felis. Afipia, derived from the abbreviation AFIP, where the type strain of the type species was isolated. They reported that the CSD bacillus and five cat scratchlike strains represent separate species in the new genus Afipia. Despite the identification of Afipia felis, as the causative agent of CSD, the pathogenesis of CSD remained incomplete until new information emerged in early 1990s, when Relman’s study concerning the etiology of bacillary angiomatosis in AIDS-related syndromes identified Rochalimaea quintana, the causative agent of trench fever as a pathogen (7). This study led to the isolation and characterization of another agent, Rochalimaea henselae, and its role as an etiologic agent in bacillary angiomatosis (8, 9). In 1992, Regnery et al (10) reported that R henselae has been found in blood or tissues of patients with bacillary angiomatosis, peliosis hepatis, and in patients with fever alone or fever associated with HIV-related syndromes. The similarities between CSD and bacillary angiomatosis had led them and other scientists to speculate that they were possibly caused by the same organism (8 –10). Regnery et al (10) reported that 88% of their patients with clinically suspected CSD had high serum titers to R henselae antigen. They concluded that serologic assays based on R henselae might be useful for diagnosis of CSD. Studies by Perkins et al (11), based on serologic and polymerase chain reaction (PCR) assays also, seemed to refute A felis, formerly known as the “cat scratch bacillus,” and suggested that Rochalimaea species may be responsible for most cases of CSD. In 1993, Dolan et al (12) were able to culture R henselae from lymph nodes of two patients suspected of having CSD, confirming that it was the most likely causative agent of CSD. Finally, as genotypic studies of the genera Rochalimaea and Grahamella revealed their close hemology to Bartonella bacilliformis and their remoteness from the Richettsiales, the genera Bartonella and Rochalimaea were united (13). The name Bartonella was preferred because it had nomenclatural priority over Rochalimaea. Bartonella hensellae an intracellular bacillus is now considered the principle cause of CSD (14). Other pathogens such as Bartonella elizabethe, or A felis might be the cause in small percentage of CSD patients in whom no evidence of B henselae can be found (15, 16). The disease is transmitted by the bite or scratch of an infected cat or kitten. The cat flea has also been shown to be a possible transmission vector among humans (14). The infected individual often develops an erythematous papule, vesicle, or pustule at the site of inoculation followed by a systemic reaction within few days. The symptoms include regional lymphadentis, fever, chills, malaise, night sweats, headache, and fatigue. Less commonly, more severe and disseminated form of the disease may develop, associated with encephalopathy, aseptic meningitis, neuroretinitis, optic neuritis, granulomatous hepatitis, pneumonia, pleural and pericardial effusions, and other widespread systemic disease (14, 15). Editorials