Most Likely Diagnosis: Dementia with Lewy Bodies (DLB)
This patient's presentation of visual hallucinations, cognitive impairment (MoCA 17/30), executive dysfunction, and sleep disturbances over 2 years is most consistent with Dementia with Lewy Bodies (DLB). 1, 2
Clinical Reasoning
Core Features Present
This patient demonstrates the hallmark constellation of DLB symptoms:
Visual hallucinations: Recurrent, well-formed visual hallucinations are a core clinical feature of DLB and often appear early in the disease course 3, 1, 2. These hallucinations typically involve people, animals, or objects and are highly characteristic of DLB rather than Alzheimer's disease 1, 2.
Cognitive impairment with executive dysfunction: The MoCA score of 17/30 indicates dementia-level impairment 1. The 2-year history of difficulty completing tasks points to executive dysfunction, which is characteristic of DLB's neuropsychological profile involving attention, executive functioning, and visuospatial abilities 4.
Sleep disturbances: The sleep problems likely represent REM sleep behavior disorder (RBD), which is a core feature of DLB and may precede other cognitive symptoms by years 1, 2. RBD involves acting out dreams during sleep due to lack of normal muscle paralysis during REM sleep 1.
Diagnostic Differentiation
The National Institute on Aging-Alzheimer's Association guidelines explicitly state that when evaluating MCI or dementia, clinicians should seek evidence for "Parkinsonism, including prominent visual hallucinations, and rapid eye movement sleep abnormalities, often seen in dementia with Lewy bodies" to distinguish it from Alzheimer's disease 4. This patient's presentation matches this profile precisely.
The presence of prominent visual hallucinations combined with cognitive impairment and sleep disturbances excludes a primary Alzheimer's disease diagnosis, even if amyloid pathology were present, as the clinical syndrome is dominated by DLB features 1.
Why Not Alzheimer's Disease?
- Alzheimer's disease typically presents with prominent memory impairment first, whereas this patient's executive dysfunction and visual hallucinations are more prominent 4
- Visual hallucinations are not a core feature of Alzheimer's disease and when present, suggest alternative or mixed pathology 4
- The early appearance of visual hallucinations and sleep disturbances strongly favors DLB over AD 1, 2
Clinical Implications
The 2025 Alzheimer's Association guidelines specifically identify "progressive cognitive-behavioral-parkinsonism syndrome" with fluctuating cognition, recurrent visual hallucinations, and REM sleep behavior disorder as characteristic of Lewy body disease 4. This patient fits this syndromic diagnosis.
Important Diagnostic Considerations
Rule out delirium: Before confirming DLB, evaluate for infections, dehydration, medication adverse effects, and metabolic disturbances that could cause acute confusion and hallucinations 3
Assess for parkinsonism: While not mentioned in this case, examine for bradykinesia, rigidity, tremor, or postural instability, which would further support the diagnosis 1, 2
Evaluate fluctuating cognition: Ask about pronounced variations in attention and alertness occurring over minutes, hours, or days 1
Confirm RBD: Obtain detailed sleep history from bed partner about dream enactment behaviors 1
Management Implications
Cholinesterase inhibitors (particularly rivastigmine) are first-line treatment for both cognitive symptoms and visual hallucinations in DLB 3, 2, 5. These should be initiated promptly.
Critical warning: Traditional antipsychotics must be absolutely avoided due to severe neuroleptic sensitivity that significantly increases morbidity and mortality in DLB patients 1, 2, 5.