This USMLE Step 1 Question of the Day involves a 60-year-old woman with progressive cognitive decline, fluctuating mental clarity, mild tremors, slowed movements, and balance issues. She has also been seen conversing with her deceased partner. Based on these clinical features, identify the most likely diagnosis.
A 60-year-old woman comes to the clinic accompanied by her daughter for a follow-up appointment for cognitive decline. During the past 2 years, the daughter says the patient has been having difficulty managing her accounts and is often confused. She has some “good days” when she manages the household and some “bad days” when she is confused and needs assistance. The patient’s partner passed away 3 years ago from a myocardial infarction, and in the past few months, her daughter found the patient talking to him as though he is in the room. About 6 months ago, the patient started having a mild resting tremor in her right hand. Since then, the patient’s movements have slowed down, and she often loses balance. Vitals are within normal limits. No orthostasis is seen. On physical examination, the patient has a flat affect, and a resting tremor is noted in the right hand. The patient walks slowly with small steps and has a kyphotic posture. Which of the following is the most likely diagnosis?
A. Progressive supranuclear palsy
B. Parkinson disease
C. Frontotemporal dementia
D. Dementia with Lewy bodiesE. Multiple system atrophy
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
D. Dementia with Lewy bodies
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
A. Progressive supranuclear palsy
Incorrect: Progressive supranuclear palsy (PSP) is a neurodegenerative disease characterized by personality and behavior changes, parkinsonism, loss of balance and vertical eye palsy. The absence of vertical eye palsy and marked personality changes favors another diagnosis.
B. Parkinson disease
Incorrect: If Parkinson motor symptoms are present for more than 1 year before dementia, the diagnosis is Parkinson disease dementia. If dementia appears before or together with the motor symptoms, or less than a year after, the diagnosis is considered dementia with Lewy bodies. This patient had signs of dementia a year and a half before motor signs.
C. Frontotemporal dementia
Incorrect: Frontotemporal dementia, formerly known as Pick disease, is characterized by early personality and behavior changes or aphasia. Patients with frontotemporal dementia may also have associated movement disorders (e.g. parkinsonism). This patient has not had marked personality changes. Additionally, parkinsonism, if present, occurs very late in the course of the disease.
E. Multiple system atrophy
Incorrect: Multiple system atrophy (MSA) is a group of neurodegenerative syndromes with similar underlying brain pathology that are characterized by parkinsonism, autonomic dysfunction, cerebellar abnormalities, and corticospinal degeneration. This patient has no autonomic dysfunction (e.g. orthostatic hypotension), which favors another diagnosis. Additionally, in contrast to idiopathic Parkinson disease, patients with MSA have preserved cognitive function.
Main Explanation
This patient is presenting with progressive dementia, cognitive fluctuation (“good” and “bad” days), and recent onset of parkinsonian signs, all favoring the diagnosis of dementia with Lewy bodies (DLB).
DLB is a common type of degenerative dementia. In addition to dementia, a patient with DLB must have at least 2 of the 4 core features, including:
cognitive fluctuations
visual hallucinations
rapid eye movement (REM) sleep behavior disorder
parkinsonism, which is characterized by the 4 clinical signs of tremor, rigidity, akinesia, and postural instability (TRAP)
Patients typically show an early decline in executive function (e.g. calculations), and visuoperceptual ability (e.g. missing traffic signs). The diagnosis of DLB is based upon the presence of core clinical features, history, and physical examination. MRI will likely show nonspecific diffuse cortical atrophy. The hallmark of the disease is the presence of Lewy bodies on pathological examination of the brain; these are eosinophilic intracytoplasmic inclusions containing aggregated alpha-synuclein in the deep cortical layers.
The differentiation of Parkinson disease from DLB is typically based on the timeline in which symptoms occur. If Parkinsonian motor symptoms are present for more than 1 year before dementia, the diagnosis is Parkinson disease dementia, whereas if dementia occurs concomitantly with or before parkinsonian motor signs, or no more than a year after onset, it is considered dementia with Lewy bodies.
Several neurodegenerative conditions may present with the classic signs of PD (e.g., tremor, rigidity) which may be hard to differentiate. These conditions are often referred to as Parkinson-plus syndromes and include multiple system atrophy, progressive supranuclear palsy, and DLB. Each has unique features that may help in establishing the diagnosis.

Major Takeaway
Dementia with Lewy bodies is a neurodegenerative condition characterized by dementia and at least two of the following features: cognitive fluctuations, visual hallucinations, rapid eye movement (REM) sleep behavior disorder, and parkinsonism. In contrast, if parkinsonism symptoms are present for more than a year before the onset of dementia, it is officially classified as Parkinson disease dementia.
References
- Parkinson-Plus Syndromes: Clues to Diagnosis, Multiple System Atrophy, Progressive Supranuclear Palsy. (2019, November 9). Retrieved from https://emedicine.medscape.com/article/1154074-overview.
- Postuma RB, Berg D, Stern M, et al. MDS clinical diagnostic criteria for Parkinson’s disease. Mov Disord. 2015;30(12):1591-1601. doi:10.1002/mds.26424
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