60 | Not just delirium: post-infectious autoimmune encephalitis in an older adult—acute illness unveiling hidden frailty and the value of multidisciplinary care

M.L. Summa, R.T. Benedetto, M. Occhiuto, P. Magnani, S. Andaloro, F. Rognoni, V. Tiraferri, M. Giovinale, M.L. Burzo, M. Mastropasqua, F. Costanza | UOC Medicina Interna, Ospedale Santo Spirito, ASL Roma 1.

Introduction. In older adults, preserved functional reserve may conceal underlying frailty that becomes evident during acute illness. Neuropsychiatric symptoms are often attributed solely to delirium secondary to systemic infection, which may delay recognition of primary or para-infectious inflammatory brain disorders.

Case description. A 77-year-old man with mild cognitive impairment (MCI), otherwise independent in activities of daily living and instrumental activities of daily living, was admitted for acute agitation, hallucinations, delusions and fever. A nasal swab was positive for Influenza A and chest imaging showed pneumonia, initially supporting infection-associated delirium. Persistent triphasic slow waves on EEG and CT evidence of normal-pressure hydrocephalus prompted further work-up. Brain MRI demonstrated post-contrast meningeal enhancement consistent with an inflammatory process. Lumbar puncture was performed and was negative for common pathogens, viruses and paraneoplastic/onconeural antibodies. Failure of antiviral therapy with acyclovir and further neurological deterioration, including dysphagia and aphasia, raised suspicion of post-infectious autoimmune encephalitis; high-dose intravenous corticosteroids led to clinical improvement. The course was complicated by acyclovir-associated acute kidney injury and multidrug-resistant bacterial infections, successfully managed through a multidisciplinary and nutritional approach. The patient was discharged to a neurorehabilitation program aimed at restoring functional autonomy.

Conclusions. Delirium may be the only clinical clue to pre-existing but compensated frailty. Moving beyond diagnostic anchoring on infection alone is essential to identify treatable neurological conditions and to enable timely rehabilitation.