pseudodementia and depression – the role of neurocognitive testing

Discriminating between depression and dementia is a differential diagnostic challenge: both are  highly prevalent conditions in the elderly, both can be present with similar symptoms (Da Silva Novaretti, D´Ávila Freitas, Mansur, Nitrin and Radanovi, 2011). To diagnose depression, there must be at least either loss of interest or persistent sadness for the majority of the day on most days in the past 2 weeks, as well as at least 3 more of 7 symptoms such as altered sleep, suicidal ideation, decreased concentration, etc.. Dementia, on the other hand, is diagnosed as a mild or severe neurocognitive disorder according to the DSM V. The neurocognitive criteria are defined as cognitive performance decreases compared to the baseline level resulting in  impairments in everyday life. 

Dementia and depression seem very different diseases at first but at a second glance there is a small yet very important overlap in the cognitive impairment symptomatology. Although dementia is more strongly associated with cognitive decline, an impairment is also seen in depression (Christensen, Griffith, MacKinnon, Jacomb & 1997). This is an often underestimated source for misdiagnosis: the depression is diagnosed as dementia the so called pseudo-dementia. Fundamentally, diagnostic criteria show that both disorders can produce a wide variance in phenotypes, which makes them hard to classify in the first place. Making it even more difficult, both disorders are correlated and present as common comorbidities especially at higher age. Depression is even proven to be a risk factor for subsequent dementia (Sahin et al., 2017).  

Because of the phenotypic similarities of both disorders, comprehensive neurocognitive testing is crucial to provide clarification. Depression is more related with executive dysfunction (Fossati, Ergis & Allilaire, 2002), physical tasks, speed and vigilance (Christensen et al., 1997) while dementia is primarily associated with memory loss (Grady et al., 1988), which should result in different test performances. 

Past research has attempted to find testing procedures that can separate depression from dementia. The most studied form of dementia in this context is Alzheimer’s disease, as this is the most prevalent form. A meta-analysis from 1997 showed that Alzheimer patients performed worse on all administered psychological tests in comparison to depressed patients with the size of the effect varying over different tests, which validates the idea of differentiating the two through cognitive testing.

Especially, verbal fluency tasks have often been discussed in the diagnostics of AD and depression (Henry & Crawford, 2005), although their role in their differentiation is not yet clear. Findings by Geffen, Bate, Wright, Rozenbilds and Geffen (1993) highlight a dissociation between the performance of the two patient groups in both versions of the verbal fluency tasks – phonemic and semantic – with a significant difference in the semantic though not in the phonemic verbal fluency.  Henry and Crawford (2005) compared several studies and discovered a larger difference between phonemic and semantic verbal fluency for dementia patients than for depressed patients, which supports a possible double dissociation. Further, Geffen et al. (1993) demonstrated that – in contrast to depressed patients – demented patients did not benefit from semantic cueing, pointing towards a specific semantic impairment in Alzheimer´s which could explain the different performance patterns. Alternatively, the differences in the verbal fluency tasks could potentially derive from speech and language difficulties. While AD patients typically show lexical access difficulties, depressed patients show slowed, less fluent and dysprosodic speech (Da Silva Novaretti et al., 2011). To investigate the potential of speech as a differential diagnostic tool, ki:elements is conducting current studies.