Background <p>Neurologically predominant fat embolism syndrome (FES) without respiratory involvement is very rare in elderly patients with pre-existing dementia. Diagnosis is challenging as symptoms may be misattributed to delirium.</p> Case presentation <p>We report the case of an 82-year-old man with dementia with Lewy bodies who developed progressive altered consciousness following a femoral neck fracture. Despite the absence of respiratory symptoms, brain magnetic resonance imaging revealed the characteristic findings of cerebral fat embolism, including multiple hyperintense lesions on diffusion-weighted imaging(DWI) and numerous hypointense lesions on susceptibility-weighted imaging(SWI) of the corpus callosum, cerebellum, and cerebrum. The patient’s clinical stability indicated conservative management was appropriate. Comprehensive supportive care included enteral nutrition, prevention of immobility-related complications, and rehabilitation. Corticosteroid therapy was not indicated. Gradual neurological improvement occurred over 84 days, with the patient achieving partial functional recovery including functional communication and mobility. Follow-up MRI at 2 months showed persistent microhemorrhages with minimal interval change, despite significant clinical improvement.</p> Conclusions <p>This case highlights the diagnostic challenges of neurologically predominant FES in elderly patients with dementia, where symptoms may easily be confused with hypoactive delirium. Advanced MRI sequences (DWI and SWI) are essential for diagnosis. Despite advanced age and pre-existing cognitive impairment, prolonged neurological recovery is possible with sustained supportive care, emphasizing the importance of avoiding premature therapeutic nihilism in this vulnerable population.</p>