Definition of Aggression, Agitation, Hyperactivity, and Irritability in Dementia
Aggression, agitation, hyperactivity, and irritability constitute common behavioral and psychological symptoms of dementia (BPSD), which are prevalent across different neurodegenerative dementia disorders.
As for other BPSD, there are no clear definitions of these entities, for which there is consensus, and no consensus as to what specific behavior may be considered agitated behavior, aggressive behavior, signs of irritability, or hyperactivity. Nevertheless, efforts have aimed at establishing definitions . Definitions of behaviors are important in order to enable valid research on, e.g., prevalence and trials investigating interventions for aggression, agitation, hyperactivity, and irritability.
Most controversy surrounds agitation and aggression and how or whether these should be considered separate types of behavior. Cohen-Mansfield defined four subtypes of agitation: physically aggressive/nonaggressive and verbally aggressive/ nonaggressive, in the development of the Cohen-Mansfield Agitation Inventory (CMAI) . Conversely, the behavioral disturbances in AD (BEHAVE-AD) scale , an often-used scale for assessment of BPSD (see Sect. 188.8.131.52 “Aggression”), considers agitated behavior as a subtype of aggression and inappropriate behavior as activity disturbances, not agitation. In the Neuropsychiatric Inventory (NPI), a single item (agitation/aggression) rates both behaviors, but in later versions, two distinct items have been added . The NPI further separately rates aberrant motor behavior, which is sometimes considered a form of agitation. The International Psychogeriatric Association has suggested a clinical and research definition of agitation, which adopts a similar perspective of that of Cohen-Mansfield (i.e., aggressive behavior is a subtype of agitation) and includes “excessive motor activity” . The issue of aberrant motor behavior/excessive motor activity is further compounded by the inclusion of this behavior (together with agitation and irritability) into a hyperactivity subsyndrome . Whether a separation of agitation and aggression is warranted from a clinical, neurobiological, or treatment point remains unresolved. It should be highlighted that these types of behavior often coexist. It has been widely suggested that subsyndromes of BPSD exist [5-7], i.e., clusters of symptoms appearing more frequently, and that such syndromes have construct validity in that, e.g., underlying pathology may be specific for these subsyndromes, that they may appear in different dementia stages, or that specific therapy is needed for different subsyndromes. However, there is no consensus regarding which subsyndromes exist and what symptoms may be considered belonging to these subsyndromes, although agitation, hyperactivity, mood, and psychosis subsyndromes are consistently identified. This also applies to nomenclature so that similar but not completely identical subsyndromes are named differently by different investigators [5-7]. Moreover, some subsyndromes are based on statistical analysis of collected data (e.g., factor analysis  and latent class analysis ), whereas others are based on theoretical or clinical considerations. Hence, clear boundaries delineating the four concepts, which this chapter discusses, cannot be specified, and a specific behavior in a patient may therefore be considered agitated, aggressive, hyperactive, and irritable.
It is important to highlight that a possible definition should not lead to a metamorphosis into definite diagnoses. Aggression, agitation, hyperactivity, and irritability are not disease entities but rather symptoms of underlying illness or physical and psychological unease at which diagnostic and therapeutic efforts should be aimed.