Large neutral amino acid changes and delirium in febrile elderly medical patients

A hypothesized but unexplored mechanism for delirium in older persons is th at changes in plasma large neutral amino acid (LNAA) concentrations alter b rain serotonin levels, result in neurotoxicity, or both. Therefore we perfo rmed a prospective study of 21 acutely febrile long-term-care residents to study the relationship between LNAA. changes and delirium. Plasma LNAA conc entrations were evaluated during illness and 1 month later. Delirium was di agnosed by using the Confusion Assessment Method. Other data included age, body mass index, cognitive impairment, comorbidity, gender, maximum tempera ture, and medication use. Seven subjects (33%) were delirious during febril e illness. Although the phenylalanine (PHE)/LNAA ratio was higher during il lness in both delirious and nondelirious groups, a two-sample 1 test demons trated that delirium was associated with a higher illness PHE/LNAA ratio (p = .03). The amount of change in PHE/LNAA from illness to recovery was not different between the delirious and nondelirious groups. Tryptophan/LNAA wa s not associated with delirium during illness or at recovery. These finding s identify another potentially fruitful area of investigation for the preve ntion anti treatment of delirium in older persons.