Laboratory and Neuroimaging Tests for Delirium
Following basic principles of history and examination, diagnosis of delirium is often aided by a range of clinical and laboratory-based investigations (Table 7.5). The most common investigations involve blood and urine tests aimed at determining underlying organic causes and risk factors of delirium. Radiological and functional studies are also occasionally used in conjunction with basic investigations. Expert interpretation is required when it comes to the context of organic pathology as a cause of delirium. Frequently, investigations may be reported as abnormal or incidental with a limited or mixed role when it comes to an immediate cause of delirium. For example, altered (slow-wave) electroencephalography (EEG) activity can be present in both delirium and dementia (e.g., Alzheimer’s disease) and thus may necessitate reference with any preceding records. Conversely, structural changes of cerebral white matter hyperintensities and general and medial temporal lobe atrophy are thought to be usually associated with dementia and unrelated to delirium incidence or severity . Examples of investigations used as a diagnostic adjunct are listed in Table 7.5. 123I-FP-CIT SPECT imaging can also be helpful in differentiating delirium from other causes of neuropsychiatric symptoms (e.g., dementia with Lewy bodies, Parkinson’s disease with and without dementia, and atypical causes of parkinsonism such as corticobasal degeneration and multiple system atrophy) though abnormal scans need to be interpreted in the context of other potential confounders such as cerebrovascular disease. More recently, animal studies hint at the potential competitive inhibition of certain medications (e.g., benzodiazepines, antipsychotics) with the presynaptic binding of the FP-CIT tracer though the clinical significance of this remains uncertain .