Exploring the effects of COVID-19 on verbal memory function in schizophrenia: Multiple case study and brief literature review

Individuals recovering from COVID-19 may experience persistent impairment in verbal memory performance, potentially due to illness-related hippocampal injury. Although verbal memory dysfunction is central to schizophrenia, the interactions between this vulnerability and COVID-19 remain unclear, with no imaging studies addressing the issue to-date. To explore this gap and generate hypotheses for future research, we adopted a multiple case study approach. Two pairs of individuals with an ICD-10 diagnosis of schizophrenia were selected, each consisting of one case with a positive COVID-19 anamnesis and one without. We calculated the Reliable Change Index to estimate the clinical significance of verbal memory performance changes, with annualized change rates in hippocampal volumes assessed against normative data. Compared to their matches, COVID-19 positive cases did not show mutually consistent changes in verbal memory performance: one case experienced a significant decline in verbal memory and learning, while the other showed a general normalization of test scores. Left hippocampal volumes showed a comparatively slowed increase, while the right hippocampi decreased in volume, although these atrophy rates did not exceed those expected in general population samples. Based on these findings, we hypothesize that COVID-19 alone does not lead to verbal memory decline in schizophrenia. Instead, the relationship between the diseases may depend on additional factors. Our case pairs differed in body mass index, systolic blood pressure, sex, phase of illness, and whole grey matter volume trajectories, leading us to hypothesize that these variables represent additional predictors or moderators of this relationship.