These limitations notwithstanding, our neuroimaging study reveals gross brain structural differences between PSU and ALC that may have implications for different treatment approaches of polysubstance dependence and alcohol dependence. The findings complement previous neuronal and glial differences we detected in the frontal lobe of these substance dependent groups (Abé et al., 2013). Here, we confirmed commonly reported smaller lobar GM and cerebellar volumes and more sulcal CSF in one-month-abstinent middle-aged ALC compared to age-matched LD. However, these volume measures were largely unaffected in one-month-abstinent alcohol dependent PSU. Furthermore, PSU had larger lobar WM volumes than both ALC and LD. The larger WM and the lack of apparent GM volume loss in PSU, despite a very long drinking history similar to that of ALC who showed marked cortical GM volume loss, suggest hypertrophic processes in short-term abstinent PSU, perhaps astrogliosis associated with neuro-inflammation. These processes may mask underlying cortical GM tissue loss associated with chronic polysubstance misuse.
