Phenomenology of the subtypes of delirium: phenomenological differences between hyperactive and hypoactive delirium

The purpose of this study was to examine the differences in phenomenology between hypoactive and hyperactive subtypes of delirium, and specifically to determine the comparative prevalence of perceptual disturbances (e.g., hallucinations) and delusions in these two subtypes of delirium.

We conducted an analysis of Memorial Delirium Assessment Scale (MDAS) items in a set of 100 delirium cases evaluated and treated at Memorial Sloan-Kettering Cancer Center (MSKCC) utilizing an MSKCC Institutional Review Board (IRB) approved Clinical Delirium Database. Individual MDAS items, reflecting the phenomenology of delirium, were compared in delirious patients classified as to motoric subtype (hypoactive versus hyperactive based on MDAS item no. 9, psychomotor activity). Particular attention was paid to differences between subtypes as to the prevalence of perceptual disturbances (MDAS item no. 7) and delusions (MDAS item no. 8).

Significant differences were found between hyperactive and hypoactive subtypes of delirium for the presence and severity of perceptual disturbances and delusions; with perceptual disturbances (e.g., hallucinations) and delusions being significantly more prevalent in hyperactive than in hypoactive delirium. The prevalence of perceptual disturbances was 50.9% and the prevalence of delusions was 43.4% in patients with hypoactive delirium. In patients with hyperactive delirium, the prevalence of perceptual disturbances was 70.2% and the prevalence of delusions was 78.7%. The prevalence of perceptual disturbances and delusions in both subtypes of delirium was significantly correlated with the presence of moderate-to-severe disturbance of consciousness/arousal (MDAS item no. 1) and attention impairment (MDAS item no. 5), but was not correlated with the presence of moderate-to-severe cognitive impairment (MDAS item nos. 2-4).

Contrary to earlier studies, which indicated extremely low prevalence rates of perceptual disturbances (e.g., hallucinations) and delusion in hypoactive delirium, our study demonstrates that the prevalence of perceptual disturbances and delusions in hypoactive delirium is much higher than previously reported (50.9% and 43.4%, respectively), and deserving of clinical attention and intervention.