3 Two Dominant Post-COVID Subtypes in Patients Seeking Treatment for “Brain Fog” Through a Post-COVID Treatment Clinic
Authors: Lokken Kristine , Robinson Jamie Hansel , Kennedy Richard , Vance David E , Lazar Ronald M , Martin Roy C , Greenfield Melissa J , Wheeler Pariya F , Gerstenecker Adam 
Published: December 2023

Objective:To examine patterns of cognitive function among a clinical sample of patients seeking treatment for Post-Acute Sequelae of COVID-19 (PASC).Participants and Methods:One hundred nineteen patients each completed a baseline neuropsychological evaluation, including clinical diagnostic interview, cognitive assessments, and a comprehensive battery of self-report questionnaires. Patients had a mean age of 50 years (range:18 to 74, SD=10.1) and a mean of 15.5 years (SD=2.54) of formal education. Patients were primarily female (74%) and of White/Caucasian race (75%). Hierarchical agglomerative clustering was used to partition the data into groups based on cognitive performance. Euclidean distance was used as the similarity measure for the continuous variables and within-cluster variance was minimized using Ward’s method. The optimal number of clusters was determined empirically by fitting models with 1 to 15 clusters, with the best number of clusters selected using the silhouette index. All analyses were conducted using the NbClust package, an R package for determining the relevant number of clusters in a data set.Results:Clustering yielded two distinct clusters of cognitive performance. Group 1 (n=57) performed worse than Group 2 (n=62) on most cognitive variables (including a brief cognitive screener and tests of attention/working memory, executive function, processing speed, learning and delayed recall). Of note, there were no significant differences between groups on an infection severity scale, hospitalizations/ICU admissions, initial or current COVID-19 symptoms, or prior comorbidities. Groups did not differ in age or gender, but Group 1 had a lower education level than Group 2 (M=14.7, SD=2.45 vs. M=16.2, SD=2.42; p=.001). Group 1 also had significantly more minorities than Group 2 (40% vs. 8%; p<.001). No other demographic differences (income, living arrangement, or marital status) were observed. In comparison to Group 2 patients, Group 1 patients self-reported significantly higher levels of anxiety and depression and functional impairment (Functional Activities Questionnaire: M=11.3, SD=8.33 vs. M=7.65, SD=7.97), perceived stress (Perceived Stress Scale: M=24.7, SD=7.90 vs. M=20.3, SD=7.89), insomnia (Insomnia Severity Index: M=16.0, SD=6.50 vs. M=13.1, SD=6.76), and subjective cognitive functioning (Cognitive Failures Questionnaire: M=58.8, SD=16.9 vs. M=50.3, SD=18.6; p’s<.05).Conclusions:Findings indicate two predominant subtypes of patients seeking treatment for PASC, with one group presenting as more cognitively impaired and reporting greater levels of anxiety, depression, insomnia, perceived stress, functional limitations, and subjective cognitive impairment. Future directions include follow-up assessments with these patients to determine cognitive trajectories over time and tailoring treatment adjuncts to address mood symptoms, insomnia, functional ability, and lifestyle variables. Understanding mechanisms of differences in cognitive and affective symptoms is needed in future work. Limitations to the study were that patients were referred for evaluation based on the complaint of “brain fog” and the sample was a homogenous, highly educated, younger group of individuals who experienced generally mild COVID-19 course.