Cognition in treatment resistance

Patients with treatment-resistant schizophrenia or schizoaffective disorder have the most severe form of the illness at least as determined by persistence of positive symptoms, but the other aspects, including negative and cognitive impairments, are typically not as well assessed clinically or in research. Most clinicians may assume that treatment-resistant patients, who often have profound functional deficits, have worse cognition than patients who respond to non-clozapine antipsychotics. This is an hypothesis that requires investigation, and a team from New Zealand have recently published such a study. They went further and also looked at the cognitive status of a group of clozapine-resistant (ultra-resistant) patients.

The 51 patients were recruited from outpatient and inpatient settings; 5 had schizoaffective disorder and the rest had schizophrenia. The control group comprised 22 healthy adults matched for age and sex. The mean age of the subjects was about 33 years. The researchers classified the patients into 3 groups based on treatment response: first-line antipsychotic responders (n=16), treatment-resistant but clozapine responders (n=20), and clozapine nonresponders (ultra-resistant; n=15). The latter group had a 8-week trial of monotherapy, and all ended up on at least 2 antipsychotics, most often clozapine and a another second-generation antipsychotic. Despite the designations, the 3 groups had no significant difference in PANSS total or subscale scores at the time of evaluation. The mean antipsychotic dose as measured in chlorpromazine equivalence was significantly greater in the clozapine-resistant group, but the mean duration of illness did not differ among groups. The control group had slightly greater mean educational attainment than the treatment-resistant group.

The cognitive assessments consisted of neuropsychologic tests covering the domains of the MATRICS Consensus Cognitive Battery developed by the U.S. National Institutes of Mental Health, considered the standard in psychosis cognitive evaluation. In this study, the testing was computerized and included such domains as executive function, social recognition, processing speed, and verbal and nonverbal learning and memory. The raw scores were converted to Z-scores normalized for age, sex and education.

The results showed that the patients overall had significant impairment in cognitive performance compared with healthy subjects, but the differences among the 3 patient groups were minimal. The treatment-resistant group, however, had a mean verbal fluency Z-score equal to that of the control group whereas the other patient groups had significantly worse performance in this domain, but subsequent analysis did not support a significant difference in verbal fluency performance in patient groups or controls. The researchers mention that pre-existing work has found that clozapine is associated with improvement in verbal fluency, an intriguing finding especially since in this study, verbal fluency was correlated with the negative-symptoms subscale of the PANSS in patients who responded to clozapine monotherapy.

The study is small, and the equivalent positive symptoms scores in the 3 patient groups raises questions about the distinctions based on treatment response, the findings tend to disconfirm the hypothesis that treatment resistance as defined by antipsychotic response necessarily indicates greater cognitive impairment.

Anderson VM, McIlwain ME, Kydd RR, Russell BR. Does cognitive impairment in treatment-resistant and ultra-treatment-resistant schizophrenia differ from that in treatment responders? Psychiatry Res. 2015; published online Oct 2015; http://dx.doi.org/10.1016/j.psychres.2015.10.036