[One homeless person out of ten suffers from cognitive disorders: What do we know about these impairments? A systematic review of homeless people's cognition].

OBJECTIVES

Homelessness is associated with several issues (psychiatric and neurological disorders, neurodevelopmental difficulties, malnutrition…) which are also risk factors for cognitive disorders. However, little is known about the relationship between the cognition of homeless people and these eventual explicative etiologies. The aim of this work is to complete the results of Depp et al. about cognition in homelessness by proposing a systematic review of the neuropsychological disorders of homeless people associated with an analysis of the etiologies likely to explain these disorders.

METHODS

We followed the PRISMA recommendations to build up this work. We analyzed the abstracts of 385 papers found on databases PSYCINFO and PubMed. Twenty-two studies have been selected for respecting our criteria (at least one valid neuropsychological test ; general group of homeless people and not a sub-group of this population ; study published in English). The prevalence quality has been evaluated through the criteria of Loney et al. Cognitive scores and etiological factors have been compared between studies.

RESULTS

The 22 studies represent only nine countries. More than half of them are considered as having a poor prevalence quality. In total, 4,256 participants have been evaluated. Their mean age was around 40 years, and 85 % of the participants were men. The results show a prevalence of cognitive disorders (MMSE) in 8.77 % of the sample. The mean IQ was 87.47 and the premorbid IQ 94.59. We also notice possible disorders affecting the episodic memory and the executive functions. Mean scores for short-term memory, speech and visuo-spatial functions are relatively low. None of the studies evaluated the praxia, the gnosia or the social cognition. The heterogeneity of studies and the lack of data did not allow us to give general conclusions about the etiology of these disorders. However, we see that around 40 % of the time subjects had histories of brain injuries and 89 % of childhood trauma. Intellectual disability is found in 49 % of the sample of a single study. Also, 70 % of the homeless population have been diagnosed with substance-related disorders and 65 % with psychiatric disorders. It appears that the only factors correlated with cognitive disorders would be the history of brain injuries and childhood traumas.

CONCLUSIONS

We confirm that homeless people often suffer from cognitive difficulties, and some of these difficulties (memory, executive functioning) are severe. Yet the etiology of these disorders remain relatively unknown: even if we observe a high prevalence of psychiatric, substance-related, neurodevelopmental and neurological issues by the homeless population, only a few of them (brain injury history and childhood trauma) seem to be correlated with cognition in homelessness. The potential explicative factors have been too rarely explored to bring a powerful explanation of cognitive disorders in homeless people. Further research needs to be done in order to give a more precise neuropsychological profile of the homeless population and to better understand what the disorders are rooted in. Last but not least, all this research and knowledge should be applied more to the care of homeless people by providing neuropsychological assessment and rehabilitation and by training the team to detect cognitive disorders and to support the person with a cognitive disability.