Lewy Body Dementia

Lewy body dementia (LBD) is a form of dementia caused by abnormal deposits of alpha-synuclein protein — called Lewy bodies — throughout the cerebral cortex, limbic regions, and brainstem. It is the third most common form of dementia after Alzheimer's and vascular dementia, accounting for approximately 10-15% of cases. LBD encompasses two closely related conditions: dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD), which differ primarily in the timing of cognitive versus motor symptom onset.

The hallmark features of LBD include: cognitive fluctuations (pronounced variability in attention and alertness, sometimes hour-to-hour), recurrent complex visual hallucinations (typically well-formed, detailed, and often involving people or animals), parkinsonian motor symptoms (tremor, rigidity, slowed movement), and REM sleep behavior disorder (acting out dreams physically during REM sleep).

The alpha-synuclein pathology in LBD overlaps significantly with Alzheimer's disease pathology in many patients — most people with LBD also have some degree of amyloid plaques. This overlap complicates diagnosis and may influence the response to certain medications.

LBD is frequently underdiagnosed and misdiagnosed. Cognitive fluctuations — where the person seems quite clear and alert at some times and confused and inattentive at others — are characteristic but often attributed to delirium or medication effects. The visual hallucinations may be interpreted as psychiatric symptoms leading to antipsychotic treatment, which can cause severe adverse reactions in LBD patients.

People with LBD are highly sensitive to typical antipsychotic medications, which can precipitate a severe condition called neuroleptic malignant sensitivity — causing dramatically worsened cognition, mobility, and even death. This makes accurate diagnosis critically important for safe medication management.

REM sleep behavior disorder (RBD) — where the normal muscle paralysis of REM sleep is absent, causing people to physically act out their dreams — is increasingly recognized as an early biomarker for the alpha-synucleinopathies, including LBD and Parkinson's disease. Isolated RBD diagnosed years before cognitive symptoms may indicate underlying alpha-synuclein pathology.