Diagnosis and Classification of the Schizophrenia Spectrum Disorders

336 C.A. Bousman et al.precision than current psychiatric phenotyping approaches (e.g. DSM-IV) [96]. Thenotion is predicated on the theory that impairments in neurocognitive performanceare more proximal to the underlying disease process, and thus screening for neurocognitiveimpairments will allow for early identification, treatment, and potentialprevention of the negative impact that these disorders have on families and society[97]. Neurocognitive impairment among METH users and those with psychosis hasbeen well documented with the largest deficits seen in executive functioning, learning,memory, speed of information processing, and emotion processing [98, 99]. Todate only one study has examined neurocognitive performance in MAP [100]. Inthis study, 19 participants with MAP and 20 with paranoid SCZ were administereda 4-h neurocognitive battery. The authors reported impairments for both MAP andSCZ; however, no significant differences between the two groups were observed,suggesting neurocognitive impairment in MAP and SCZ are comparable. Futureneurocognitive work in MAP, utilizing larger samples will be needed before MAP’spotential to inform identification of clinical useful neurocognitive biomarkers forSCZ can be evaluated.Neuroimaging has also recently received attention as an approach for identifyingmarkers for identification and/or differentiation of a variety of psychiatric illnesses.Several neuroimaging techniques [e.g. Positron emission tomography (PET), Singlephoton emission computed tomography (SPECT), Magnetic resonance imaging(MRI), Magnetic Resonance Spectroscopy (MRS)] are available by which imagesof the structure and function of the brain can be ascertained. To date, several neuroimagingstudies [101, 102] have been conducted related to METH abuse but onlya few neuroimaging studies related to MAP have been published (for review seeIyo et al. [103]). Among those conducted for MAP, one used PET and the othera MRS approach. In the PET study [104], the density of dopamine transporters inthe nucleus accumbens and caudate/putamen in MAP participants was significantlyless compared with controls, and it was correlated with the length of use and severityof psychotic symptoms. This is in partial concordance with a SCZ study [105]which observed a lack of brain asymmetry in dopamine transporter ligand uptake(right > left) in neuroleptic-naive SCZ patients. In the MRS study [106], MAPparticipants showed a significantly reduced ratio of creatine plus phosphocreatine(Cr + PCr)/choline-containing compounds (Cho) in the brain compared with thehealthy control participants. In addition, the reduction in the ratio of Cr + PCr/Chowas significantly correlated with the duration of METH use and with the severityof residual psychiatric symptoms. In SCZ participants, the ratio of Cr + PCr/Cho inthe left temporal lobe has been shown to be lower than in control subjects, albeitnot significant [107]. However, the Cr + PCr/Cho ratio was negatively correlatedwith the left temporal lobe gray matter and positively with left temporal lobe whitematter [107].Clearly, further research of MAP across several disciplines employing a varietyof approaches, such as imaging genomics [90, 91, 108, 109], are requiredbefore MAP is fully adopted as a feasible model for biomarker discovery in SCZ.However, the current literature points to the potential of MAP as an adjunct approachto ongoing efforts aimed at discovery of biomarkers of SCZ susceptibility and