Dementia with Lewy Bodies | Why Does Reality Seem to Fluctuate?

Cognitive fluctuation is a core feature of Dementia with Lewy Bodies (DLB) and distinguishes it from other dementias like Alzheimer's disease. This term describes significant, unpredictable variations in alertness and thinking abilities that can occur over short periods, such as from one hour to the next or day to day. A person with DLB might be lucid and coherent in the morning but become confused, drowsy, and unresponsive in the afternoon. These episodes are not simply "good days and bad days" but are pronounced shifts in cognitive function. Symptoms include disorganized speech, staring into space for long periods, excessive daytime sleepiness, or illogical flow of ideas. These fluctuations are believed to be caused by the disruption of normal neurotransmitter signaling in the brain, particularly acetylcholine and dopamine, due to the presence of Lewy bodies. Lewy bodies are abnormal aggregates of a protein called alpha-synuclein. When they form in the cerebral cortex, they impair the brain's ability to maintain consistent attention and executive function, leading to this characteristic "flickering" of consciousness.

Two other cardinal symptoms of DLB are recurrent visual hallucinations and Parkinsonism. The hallucinations are typically well-formed, detailed, and vivid, often involving people or animals. Unlike hallucinations in some psychiatric disorders, they are usually not frightening or threatening to the individual, who may have insight that what they are seeing is not real. These phenomena arise from dysfunction in the brain's visual processing pathways, caused by Lewy body deposits. Parkinsonism refers to a set of motor symptoms also found in Parkinson's disease, including muscle rigidity, slowed movement (bradykinesia), and tremors. In DLB, these motor symptoms are caused by Lewy bodies accumulating in the brainstem, an area critical for motor control. Typically, in DLB, the cognitive symptoms appear before, or within one year of, the onset of these motor difficulties.

Differentiating DLB from Alzheimer's and Parkinson's disease is critical for proper management. While all are neurodegenerative disorders, their clinical profiles differ. Alzheimer's disease primarily begins with significant memory loss. In contrast, early DLB is characterized more by problems with attention, executive function (like planning and problem-solving), and visual-spatial skills. The defining features of cognitive fluctuations, visual hallucinations, and REM sleep behavior disorder are prominent early in DLB but not in Alzheimer's. The key distinction from Parkinson's disease is the timing of symptom onset. In Parkinson's, motor symptoms precede cognitive decline by many years. In DLB, cognitive decline begins before or concurrently with the motor symptoms (within a one-year timeframe).

Visual hallucinations in DLB result from a complex interplay of factors linked to Lewy body pathology. These alpha-synuclein protein deposits disrupt brain networks, particularly in the visual cortex and pathways responsible for visual processing. This disruption leads to faulty interpretation of sensory information. Furthermore, DLB is associated with a significant deficit in the neurotransmitter acetylcholine, which plays a key role in perception and attention. The combination of structural damage to visual pathways and chemical imbalances makes the brain susceptible to generating perceptions without external stimuli, resulting in detailed and recurrent hallucinations.

A strong clinical predictor of DLB is a condition called REM Sleep Behavior Disorder (RBD). In a healthy brain, the body is effectively paralyzed during the Rapid Eye Movement (REM) stage of sleep, when most dreaming occurs. In individuals with RBD, this paralysis (known as atonia) is lost. Consequently, they physically act out their dreams, which can involve punching, kicking, shouting, or jumping out of bed. This behavior is caused by the accumulation of Lewy bodies in the brainstem, the region that regulates REM sleep atonia. RBD can precede the cognitive and motor symptoms of DLB by years or even decades, making it a crucial early indicator of the underlying disease process. It is present in over 80% of patients ultimately diagnosed with DLB.