Factors influencing treatment-induced language recovery in chronic, post-stroke aphasia

Abstract

Although there is evidence to support the efficacy of aphasia rehabilitation, individuals’ response to treatment is often variable. It is currently not possible to determine who will respond to a particular treatment and the degree to which they will recover. The objective of this thesis was to evaluate the relationship between treatment parameters, participant characteristics and aphasia therapy success for adults with chronic, post-stroke aphasia. Specifically, we investigated the effect of treatment intensity on language and communication outcomes in adults with aphasia. As anomia is a predominant characteristic of aphasia, we further sought to understand the influence of language and cognitive ability on anomia therapy outcomes. A non-randomised, parallel-group, dosage-controlled, pre-post-test design was employed. Thirty-four adults with chronic aphasia were recruited to participate in the study. Prior to commencing therapy, a comprehensive language and cognitive assessment battery was administered. Three baseline naming probes were administered in order to establish sets of 30 treated and 30 untreated items. Participants completed the comprehensive, aphasia rehabilitation program, Aphasia Language, Impairment and Functioning Therapy (Aphasia LIFT). Therapy consisted of impairment, functional, computer and group-based aphasia therapy. Participants were allocated to an intensive (LIFT; 16 hours per week, 3 weeks) versus distributed (D-LIFT; 6 hours per week, 8 weeks) treatment condition. Both groups received 48 hours of aphasia therapy. Treatment outcomes were evaluated immediately post-therapy and at 1 month follow-up. Outcome measures were collected across the World Health Organization’s International Classification of Functioning, Disability and Health domains. The outcomes of this clinical study form the basis of this thesis. Aphasia LIFT had a positive and enduring effect on measures of participants’ language impairment and functional communication. With respect to impairment-based measures of word retrieval, distributed therapy resulted in significantly greater gains on the Boston Naming Test at post-therapy and 1 month follow-up compared with intensive therapy. Aphasia LIFT resulted in comparable naming gains for treated and untreated items at post-therapy and 1 month follow-up when delivered in an intensive versus distributed schedule. At the individual level, we found a trend favouring D-LIFT with respect to the generalisation and maintenance of therapy gains for treated and untreated items. However, it is acknowledged that this is a limited sample size and further research with a larger cohort of participants is required. In addition, Aphasia LIFT was found to have a positive effect on participants’ communication activity and participation at post-therapy and 1 month follow-up, regardless of treatment intensity. Our findings suggest that a distributed treatment schedule is equally, if not more, effective than an intensive treatment schedule for adults with chronic aphasia. The remediation of word retrieval deficits was a predominant target of Aphasia LIFT. As such, we also considered the influence of language, verbal learning and cognitive ability on anomia therapy outcomes (i.e., naming accuracy for treated and untreated items). With respect to language measures, we found that lexical-semantic processing ability, as measured by the Comprehensive Aphasia Test (CAT), was a significant predictor of therapy gains for treated items. Furthermore, we found a strong, positive relationship between aphasia severity and therapy outcomes for anomia. At the individual level, participants’ locus of language breakdown was hypothesised based on a qualitative error analysis of individuals’ performance on the CAT and baseline confrontation naming probes. We found that participants with predominantly semantic deficits demonstrated the most varied response to therapy. In contrast, individuals with a hypothesised deficit mapping semantics to phonology generally responded positively to treatment. We measured participants’ verbal learning abilities using a novel word learning paradigm and found that therapy gains for treated items at post-therapy were correlated with novel word learning performance. We also evaluated the relationship between participants’ cognitive profile at baseline assessment and anomia therapy gains. We found that measures of verbal and nonverbal short-term memory, working memory and executive function significantly correlated with therapy gains for treated items at post-therapy and 1 month follow-up. Interestingly, only measures of short-term memory correlated with naming gains for untreated items. Overall, this research has advanced our knowledge of the factors influencing treatment-induced language recovery in adults with chronic aphasia. The findings of this thesis have important theoretical and clinical implications for aphasia rehabilitation. Despite increased support for intensive rehabilitation services, our results provide support for a distributed model of aphasia therapy. Furthermore, this research has contributed to our understanding of individual language and cognitive factors that may facilitate treatment-induced recovery from anomia. These findings have enhanced our knowledge of the mechanisms underlying treatment and may contribute to the development of targeted language interventions. Furthermore, the outcomes of this research may help to determine who is likely to benefit from aphasia rehabilitation and consequently support the efficacious delivery of rehabilitation services.