Mixed dementia and hyperactive delirium: a diagnostic challenge

It is well recognised that acute confusion or delirium complicates up to 10% of acute medical admissions. Disorientation in time and place with an impaired short-term memory and conscious level are the hallmarks of an acute confusion. In delirium, disorders of perception may produce restlessness and agitation. A similar state during the final days of life is termed 'terminal delirium'. Less than 10% of affected individuals will have a primary neurological disorder, for example, dementia, a neurodegenerative disease with varying aetiologies. Currently there are at least 50 million people globally suffering from dementia rendering it a global healthcare problem. Mixed dementia (MD) can be defined as a cognitive decline sufficient to impair independent functioning in daily life resulting from the coexistence of Alzheimer's disease (AD) and cerebrovascular pathology. MD occurs in patients with a neurodegenerative disorder, such as AD, Lewy body or Pick's disease and additionally cerebrovascular disease. The mechanistic synergisms between the coexisting pathologies affecting dementia risk, progression and the ultimate clinical manifestations remain elusive. Although AD can be diagnosed with a considerable degree of accuracy, the distinction between isolated AD, vascular dementia and MD, when both pathologies coexist in the same patient remains one of the most difficult diagnostic challenges because their clinical presentation can overlap. Neuropathological studies indicate that mixed vascular Alzheimer's dementia (MD) has a prevalence of 22% in the elderly. The authors present the case of a 78-year-old man with a diagnosis of MD presenting to the emergency department with delirium, a common but serious acute neuropsychiatric syndrome with the core features of inattention and global cognitive dysfunction. This case demonstrates the challenges in establishing a diagnosis in patients presenting with MD and shows that a cognitive assessment at presentation in a delirious state offers very little diagnostic information. It is therefore suggested to conduct a routine cognitive function examination on patients with dementia to anticipate new neurological signs and/or symptoms thus allowing earlier diagnosis and treatment. However, a baseline cognitive assessment when the patient was well, duration and nature of deterioration as well as collateral history will help differentiate delirium from an underlying dementia.