Rickettsia rickettsii encephalitis in Brazilian spotted fever: a case report.

Brazilian spotted fever, caused by Rickettsia rickettsii, is a life-threatening tick-borne disease endemic to southeastern Brazil and is associated with high mortality when treatment is delayed. Central nervous system involvement poses a particular diagnostic challenge because of nonspecific early symptoms and frequent misdiagnosis as dengue or leptospirosis. We report a case illustrating characteristic neuroimaging findings and therapeutic considerations in rickettsial encephalitis. We describe the clinical course, cerebrospinal fluid (CSF) findings, magnetic resonance imaging (MRI) findings, serologic results, and treatment response in a 23-year-old man who presented with febrile encephalopathy in an endemic region of Brazil. The patient had a five-day history of fever, erythematous macules, and progressive encephalopathy. CSF analysis showed elevated protein and lymphocytic pleocytosis. MRI showed T2/fluid-attenuated inversion recovery hyperintensities with restricted diffusion involving the bilateral corticospinal tracts and the splenium of the corpus callosum, forming a "boomerang" pattern. Clinical improvement followed initiation of empirical doxycycline and pulse methylprednisolone. Serologic testing supported the diagnosis of R. rickettsii infection with a positive immunoglobulin M titer of 1:512. Follow-up MRI showed near-complete lesion resolution at 4 months, with a residual splenial lesion persisting at 18 months. This case illustrates the importance of recognizing characteristic MRI patterns, including the "starry sky" and "boomerang" signs, as diagnostic clues in rickettsial encephalitis, even when the classic triad is incomplete. Early empirical doxycycline remains critical for neurologic outcomes, and adjunctive corticosteroids may have a role in selected cases when immune-mediated central nervous system injury is suspected.