Atypical Legionella pneumophila encephalopathy lacking respiratory symptoms and radiographic lesions: A Case Report.

This report details an unusual case of Legionella pneumophila encephalopathy in a 29-year-old male who presented with acute altered consciousness and extreme agitation, notably lacking any respiratory symptoms or typical meningeal signs. Extensive imaging, including chest CT and cranial MRI, revealed no pulmonary infiltrates or structural brain lesions. Cerebrospinal fluid (CSF) analysis demonstrated an aseptic profile with elevated protein, and CSF metagenomic sequencing returned negative. The diagnostic dilemma was ultimately resolved using whole-blood targeted next-generation sequencing (tNGS), which detected Legionella sequences. The patient achieved a rapid and complete neurological recovery following a combined regimen of levofloxacin and high-dose glucocorticoids. This case underscores that Legionella infection can manifest as an isolated, toxin- and immune-mediated encephalopathy without preceding clinical pneumonia. It highlights the critical rescue value of early molecular screening (such as tNGS) in unexplained encephalopathy and supports the judicious use of early steroid intervention to halt the aseptic neurotoxic cascade.