March 25th, 2021
Described for the first time in late 1980s, Dementia with Lewy Bodies (DLB) is a gradually progressive neurodegenerative disorder with insidious onset. Histopathologically, the hallmark feature of DLB is the presence of Lewy bodies in the cerebral cortex.
DLB is the third most common cause of dementia, after Alzheimer’s disease and vascular dementia. DLB accounts for 4-25% of all cases of dementia. The prevalence is calculated to be 0.1- 5%, with a male to female ratio of 1.5-4:1. The onset is typically in the sixties to seventies.
Fluctuating cognition is a core feature. Fluctuation is seen in consciousness, memory, language, and visuospatial abilities; and can occur within hours or days. It is sometimes indistinguishable from delirium. Studies have suggested at profound cholinergic deficit as the cause for the fluctuating consciousness.
Recurrent visual hallucinations
Visual hallucinations are usually well formed, vivid, and often of people and animals. According to functional neuroimaging findings, pathology affecting visual cortex and temporoparietal regions is thought to be the cause of visual hallucinations.
Features of parkinsonism
Parkinsonism occurring at least 1 year after the onset of dementia is a feature of DLB. This can also occur concurrent to, or shortly before cognitive decline; however, it should not antecede the dementia by more than 1 year.
Among the parkinsonian features, rigidity and gait abnormalities are more common than tremor. Parkinsonism occurs due to dopaminergic deficiency in the substantia nigra.
Rapid eye movement (REM) sleep behavior disorder
Changes in sleep-wake cycles are common and can be an early feature. Individuals will act out their dreams and vocalize during sleep due to absence of REM sleep induced muscle hypotonia.
Sensitivity to neuroleptic drugs
Up to 50% of the patients with DLB demonstrate severe sensitivity to neuroleptic drugs such as haloperidol and chlorpromazine. Features of neuroleptic sensitivity include sedation, rigidity, postural instability, and in some cases, even rapid deterioration and death. This is because the extensive loss of dopaminergic and cholinergic neurons due to neurodegeneration renders affected individuals more susceptible to the antidopaminergic and anticholinergic effects of neuroleptics.
Features of autonomic dysfunction include orthostatic hypotension, repeated falls, syncope, and urinary incontinence. The exact mechanism of autonomic dysregulation is unclear, but proposed mechanisms include deposition of Lewy bodies in peripheral autonomic neurons.
Other psychotic features
Non-visual hallucinations, particularly auditory hallucinations and delusions, and specifically of a persecutory nature, are common.
Depression is significantly more common in these individuals; and is suggested to be due to alterations in monoamine levels. Occasionally, the initial referral to mental health services may be due to depression.
DLB is a risk factor for falls. This probably due to postural instability secondary to parkinsonism, autonomic dysregulation, and fluctuating cognition.