Case Presentation: A 62-year-old malnourished, Hispanic man presented with fever and malaise for 1 week associated with headache. Past medical history was significant for rheumatoid arthritis treated with prolonged, unmonitored prednisone, chronic obstructive pulmonary disease, and a history of 18 cats at home. On examination, the patient was alert and oriented, febrile, and cachectic, but no regional lymphadenopathy was appreciated. During the hospital course, the patient became more agitated and required intubation. Indirect immunofluorescent antibody (IFA) testing showed negative IgM but very high IgG titers of 1:1280 which is indicative of Cat Scratch Disease (CSD). CSF analysis demonstrated pleocytosis with negative bacterial and fungal cultures. The patient was treated with doxycycline for CSD and voriconazole for concomitant scant growth of Aspergillus flavus on sputum culture. Subsequently, the patient improved with no residual neurological deficits.

Discussion: Cat scratch disease (CSD) is caused by the bacterium Bartonella henselae, typically characterized by self-limiting regional lymphadenopathy. CSD is more prevalent in immunocompromised individuals​(1)​. Neurologic complications are relatively rare. Between 0.17% and 2% of patients with CSD develop encephalopathy or other neurologic manifestations. Approximately 2 to 3 weeks into the illness, a headache develops followed by mental status changes, which may progress from delirium to an unresponsive state​(2,3)​. Diagnosis of CSD-associated encephalopathy may be challenging as normal MRI have been described despite the existence of neurological deficits​(4)​. Our patient presented with fever and headache followed by agitation on day 3 of hospital course with a normal CT head imaging. However, CSF finding with elevated WBC and protein with negative cultures and constellation of neurological symptoms suggested encephalitis. Bartonella species are difficult to culture, and it is not routinely recommended. Serology is the best initial test and can be performed by indirect fluorescent assay or enzyme-linked immunosorbent assay(​5)​. High IgG titers (> 1:256) are strongly indicative of acute active infection​(6)​. However, serologic testing has serious shortcomings, and a negative serologic test does not rule out CSD in a patient with characteristic epidemiologic and clinical features​(7,8)​. Our patient had an IgG titer of 1:1280 with negative IgM titers which is representative of acute infection.

Conclusions: This case illustrates the importance of investigating Bartonella henselae infection despite the absence of regional lymphadenopathy in an immunosuppressed patient with a history of cat exposure presenting with persistent fever. Neurological symptoms are uncommon but can occur especially with immunosuppression. Moreover, obtaining a history of animal exposure prior to initiating immunosuppressive medications is pertinent.