Cognitive Functioning and Quality of Life in Patients with Dual Diagnosis

Dual Diagnosis (DD) is the co-occurrence of a Severe Mental Illness (SMI), commonly a major psychotic or affective disorder, and a Substance Use Dependence Disorder (SUD). It is a highly prevalent disorder with a large impact in clinical and health care systems due to the complications arising from the comorbidity between both conditions. The aim of this work is twofold: the study of the cognitive performance and the Health Related Quality of Life (HRQOL) in patients with DD. The first one, because few studies have examined this question and its assessment is of great interest, since cognitive functioning is related to the clinical course and may even be a predictor of failure or success of the therapeutic interventions. Although major cognitive impairments can be expected in DD due to the additive effects of both psychiatric disorder and SUD, a wide review of published results on the scientific literature suggest that their cognitive functioning depends, among others, on the main substance of choice, the assessed cognitive domain and the age of the participants. Thus, we focus on the assessment of the executive functioning on one hand, and on the domains of attention, memory and speed of processing on the other, in a sample comprised by subjects with schizophrenia and cocaine dependence (SZ+; n = 30) compared to subjects with schizophrenia without SUD history (SZ-; n=30) and to cocaine dependent subjects without psychiatry comorbidity (COC; n=35). Although in the last decades there has been an increased interest in the Quality of Life as an assessment measure as well as an indicator of the effectiveness of interventions in both SMI and SUD, few studies had focused on DD. For this reason, the second objective of this work was to assess HRQOL in a group with DD (n = 35) and compare it to a group with SMI (n=35) and to another one with SUD (N=35) without comorbidity. Regarding the cognitive functioning, the results showed a similar pattern of performance in the SZ+ and COC groups in neuropsychological tasks related to executive functions, being their performance better than the SZ- group. This may suggest that patients with SZ+ have higher cognitive skills than the SZ- ones. Therefore, the SZ+ patients may be a subgroup of SZ with lower biological vulnerability to develop the illness and maybe, a better psychosocial premorbid functioning, making them more able to acquire the illegal substance of abuse. In the domains of attention, memory and speed of processing, the COC group performed better than both SZ+ and SZ- groups, without differences between them. However, the age was negative related to the cognitive performance in the SZ+ group. So, the older SZ+ showed worse cognitive functioning. Otherwise, the SZ- patients showed a stable cognitive functioining regardless of the age. This, in agreement with the idea of an additional cognitive impairment to the psychiatric disorder manifested in older SZ+ patients because of the long term expression of the neurotoxic consequences of consumption. Concerning HRQOL, all the groups showed lower scores compared with the normative Spanish data. The DD group showed the worst scoring in most of assessed scales and in the mental domain, while the SUD group obtained the best, and the SMI obtained intermediate scores. The worse state in the mental domain appeared strongly related to the number of suicide attempts, daily intake of medication and to the caffeine consumption, only in the DD group. The systematic assessment of the HRQOL status could be a useful tool in the detection of specific care areas, helping to improve the treatment goals as well as an assessment measure of the effectiveness of interventions applied to DD patients. Overall, our results suggest particular characteristics in subjects with DD regarding cognitive performance and HRQOL status, which make them different to the subjects with SMI and SUD. This demonstrates the interest to study DD as a specific diagnostic entity. However, further research in this field, incorporating long term measures and biological parameters, could help to a better understanding of the current knowledge in DD and to increase the benefits in the clinical management of these patients.