We identified cortical thickness of the inferior parietal lobule as the most significant predictor of relapse in Chinese male patients with AD. Age, education, smoking status, employment, age of onset, duration of illness, drinking in the morning, family history of alcoholism, mean daily drinks, and the presence of delirium or seizures did not influence the likelihood of relapse. Although in the relapsers group of our study, the variables significantly associated with the time to first re-drink were seizures and delirium, that is, the time to first re-drink was shorter in patients with seizures and delirium experienced within 3 months after withdrawal, there was no significant difference in the two variables between the relapser and abstainer groups. A recent study has also found the contribution of neurotoxicity of alcohol withdrawal syndrome to structural brain alterations. Even if the patients who experienced seizures and/or delirium tremens during acute withdrawal were not included in the study, the severity of such brain impairment may be correlated with the prognosis of patients with AD(Laniepce et al. 2020). Moreover, in another study, it was suggested that younger age at first drink and the presence of delirium during acute withdrawal predicted more severe alcohol cravings(Kaya et al. 2021). The results of our study did not support the opinion of relapse to drinking associated with clinically significant impairment (e.g., age at first drink, drinking in the morning, family history of alcoholism, presence of delirium or seizures, and mean daily drinks), except for the age of onset. The difference in results may be attributed to the enrollment of severe AD inpatients and adoption of different metrics and procedures in our study. Nevertheless, our study found a minor difference in age of onset between abstainers and relapsers, suggesting that younger age of onset may be a risk factor for relapse within 6 months. Although this variable was not successfully incorporated into the prediction model in the subsequent modeling, we should continue to pay attention to the age of onset since this point is consistent with most findings in previous studies(Moure-Rodríguez and Caamano-Isorna 2020; Rial et al. 2020; Zhu et al. 2017).
Cortical thickness is related to the number or density of cells in a column of the cerebral cortex, which is subject to the neurotoxic effects of chronic alcohol consumption. Cortical thickness was chosen as the primary measure in this study since previous work has indicated the index to be more sensitive to group differences than grey matter volume in imaging studies(Winkler et al. 2010). One study reported that focal areas of increased cortical thickness were observed in the brains of healthy male controls compared to alcoholic males(Momenan et al. 2012), and according to another recent report, cerebral cortex injury was most pronounced in the frontal and parietal cortical regions and associated with reduced glucose metabolism in patients with AD(Tomasi et al. 2019). A diminished parietal cortex may impair the allocation of attention and impulse control during high-order cognitive function(Wang et al. 2019). Another study likewise suggested that patients with AD had lower metabolic rates in the frontal, temporal, and parietal lobes compared to healthy volunteers(Bralet et al. 2022) since these brain regions were mainly involved in the rewarding neural circuit and executive control network, which are critical in inhibitory control and maintaining sobriety(Dennis et al. 2020; Gladwin et al. 2013). Additionally, craving is thought to be an important mechanism involved in the development and maintenance of AD(Koob and Volkow 2010). Impulsivity, craving, and brain damage mentioned above can be considered potential predictors of relapse in AD(Czapla et al. 2016; Durazzo and Meyerhoff 2017). In particular, along with our findings that the thickness of the IPL was most significantly decreased in relapsers than abstainers, we also demonstrated higher inattention and non-planning impulsivity in relapsers relative to abstainers, consistent with an earlier study(Czapla et al. 2016) and other work suggesting impulsive decision-making as a hallmark characteristic of AD(Dennis et al. 2020). In our study, we did not clarify the relationship between impulsive control impairment of BIS-11 and cortical thickness decrease of IPL in all AD inpatients enrolled in our study. However, if the data were not treated strictly according to the Bonferroni correction, we could also see that inattention of impulsivity was negatively correlated with the thickness of the supramarginal gyrus cortex (one of the ROIs before the Bonferroni correction), and AUQ total score was negatively associated with the cortical thickness of IPL and supramarginal gyrus. Even if the severity of alcohol craving represented by AUQ scores did not reveal the significant difference between relapsers and abstainers, the correlation between severe craving and decreased cortical thickness of ROIs is still worthy of further attention. In fact, these findings are similar to previous studies(Kose et al. 2015; Seo and Sinha 2014; Zhu et al. 2017).
Therefore, the differences in cortical thickness between abstainers and relapsers, broadly consistent with earlier studies(Durazzo et al. 2011; Rando et al. 2011), suggest the utility of the macrostructural measures in identifying patients at risk of relapse(Durazzo and Meyerhoff 2017). Similar to the results of our previous study in AD relative to controls(Yang et al. 2020), the current finding indicates inferior parietal cortical thickness as a critical marker of alcoholism. By virtue of several higher-order functions mediated by the posterior parietal cortex, different portions of the posterior parietal cortex participate in multiple cognitive processes, including sensorimotor integration, spatial attention, decision-making, working memory, early motor planning, as well as more complex behaviors(Witkiewitz 2011). As we all know, decreased cortical thickness in the anterior cingulate, frontal and parietal regions of the executive control network might explain the maintenance of addictions in terms of an impaired ‘reflective’ system, enhancing and maintaining the salience of potential punishments in working memory(Gianelli et al. 2022). According to the findings of our study, the decreased inferior parietal cortices and higher non-planning impulsivity are implicated as the risk factors of relapse in male patients with AD. Actually, keeping abstinence from alcohol dependence is a key high-order cognitive function that the IPL involves as an adaptive task-control hub of the fronto-parietal control network(Cole et al. 2013). In other words, deficient internal initiation of behavior mediated by the IPL may be sufficient to reduce goal-directed behavior and then lead to relapse for patients with AD(Martínez-Vázquez and Gail 2018; Tumati et al. 2019). Unfortunately, our study did not find significant differences in the frontal lobe, another important brain functional region in this neural network. More studies with a larger sample size would be needed to investigate the potential inter-relationship between impulse control, parietal cortical structure and function, and alcohol addiction.
Limitations
There were limitations to the present study. Firstly, the modest sample size may limit the generalizability of our findings. Future discovery research on AD must be undertaken with larger samples using prospective observational methods(Stout 2021). Secondly, our definition of relapse (i.e., any alcohol consumption) was based on the consideration that any level of alcohol resumption was associated with a poorer psychosocial function(Durazzo and Meyerhoff 2017). Other relapse metrics should be thoroughly investigated to reflect the severity of relapse in future work. Thirdly, we did not examine the influence of sex on AD relapse as we only included male patients with AD. A considerable literature suggests important sex-dependent differences in the pathophysiological processes of alcoholism(Rossetti et al. 2021). Again, more studies are needed to address this issue. Fourthly, we did not assess coping skills, stress, self-efficacy, marital status, and social support, which have all been shown to influence and/or predict drinking behavior after treatment(Le et al. 2021). Lastly, we focused on cortical thickness. Other morphometric measures including gray matter volumes and surface represent potential neural markers of AD(Chye et al. 2020).