Neurocognitive Disorders — Hippocampal Atrophy in Alzheimer Disease
A 67-year-old woman is brought by her daughter because of gradually progressive forgetfulness over 2 years; she repeats questions and misplaces items. Over recent months she has lost interest in her hobbies and withdrawn from family gatherings. Neurological examination is non-focal. MRI of the brain shows bilateral hippocampal atrophy. Which feature in this patient is most specific for Alzheimer disease?
- A.Bilateral hippocampal atrophy on MRICorrect
- B.Loss of interest and social withdrawal
- C.Onset of symptoms before age 70
- D.Female sex
Explanation
Disproportionate medial temporal and hippocampal atrophy is the structural finding most closely tied to Alzheimer disease. Neurofibrillary tangles and neuronal loss begin in the entorhinal cortex and hippocampus, which is why episodic memory fails first, and it is a recognised supportive imaging marker of neurodegeneration, although the 2024 NIA-AA criteria treat atrophy as non-specific and base the diagnosis on amyloid and tau biomarkers. Apathy and social withdrawal are the main competitor because they are common in Alzheimer disease, but they are equally typical of depression, frontotemporal dementia and vascular cognitive impairment, so they add little specificity; their real value is prompting screening for depression, a treatable mimic. Age and sex are risk factors, not diagnostic features: about two thirds of patients are women and incidence roughly doubles every five years after 65, yet onset before 70 neither confirms nor excludes the disease. Hippocampal atrophy is still not pathognomonic, because it also occurs in hippocampal sclerosis of ageing and limbic-predominant age-related TDP-43 encephalopathy. When molecular certainty matters, for example before anti-amyloid therapy, amyloid PET or cerebrospinal fluid amyloid-beta 42/40 ratio and phosphorylated tau confirm the pathology, which atrophy alone cannot do.
Why each option
- A.
- Correct. Medial temporal and hippocampal atrophy reflects the earliest site of Alzheimer neurodegeneration and is the most disease-specific feature listed here.
- B.
- Apathy and withdrawal occur in Alzheimer disease but equally in depression and frontotemporal dementia, so they are not specific to it.
- C.
- Age of onset is a risk-factor characteristic; onset before 70 neither confirms Alzheimer disease nor distinguishes it from other dementias.
- D.
- Women make up most patients with Alzheimer disease, but sex is a risk factor and cannot support the diagnosis in an individual.
Reference: NIA-AA Revised Criteria for Diagnosis and Staging of Alzheimer's Disease (Jack et al, Alzheimer's & Dementia 2024); UpToDate — Clinical features and diagnosis of Alzheimer disease
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