Behavioral Neurology
This domain asks you to name a cognitive syndrome from a described behaviour and to distinguish neurodegenerative decline from delirium and depression.
Aphasia
Broca aphasia is non-fluent with impaired repetition and preserved comprehension, from posterior inferior frontal injury. Wernicke aphasia is fluent with impaired comprehension and repetition, from superior temporal injury. Conduction aphasia affects repetition alone, from arcuate fasciculus damage. Transcortical aphasias spare repetition. Global aphasia affects all domains.
Memory and the limbic circuit
Explicit memory depends on the hippocampus and Papez circuit: fornix, mammillary bodies, anterior thalamus and cingulate. Korsakoff syndrome from thiamine deficiency causes amnesia with confabulation. Alzheimer disease begins with medial temporal atrophy, and amyloid and tau biomarkers now support diagnosis.
Behavioural and cortical syndromes
Behavioural variant frontotemporal dementia shows disinhibition, apathy, loss of empathy and hyperorality with executive deficits. Primary progressive aphasia variants are semantic (temporal pole, loss of word meaning) and logopenic (impaired repetition, often Alzheimer pathology). Right parietal lesions cause neglect; left parietal lesions cause Gerstmann syndrome with agraphia, acalculia, finger agnosia and right-left disorientation.
Worked example
A 68-year-old has progressive word-finding difficulty; speech is fluent but repetition is impaired and comprehension is preserved. This is logopenic primary progressive aphasia. Arrange MRI, which may show left posterior temporal and parietal atrophy, and consider Alzheimer biomarkers because this variant often reflects Alzheimer pathology.
Traps
Calling delirium dementia when onset is acute and attention fluctuates; diagnosing depression in a patient whose apparent apathy is aphasia; missing hearing and vision impairment as causes of apparent confusion.