25/09/2019
AACN's Ask the Experts Series:
What is the difference between cortical and subcortical dementia?
Response by Rus Bauer, PhD, ABPP
Dementia is an umbrella term that denotes a loss of cognitive and adaptive ability which impairs the person’s ability to perform everyday life functions. Dementia is not a disease itself; it is a syndrome caused by a variety of diseases including degenerative conditions (e.g., Alzheimer’s disease, Parkinson’s disease), infections (e.g., Creutzfeldt-Jacob disease), metabolic (e.g., hepatic, renal) disease, repetitive trauma (e.g., chronic traumatic encephalopathy), and other causes. The diseases that result in dementia can affect both the cortex (the brain matter responsible for higher cognitive function), as well as subcortical regions (where complex brain cells and their interconnections regulate motor, intentional, and emotional systems of the brain).
The distinction between “cortical” and “subcortical” dementia evolved in the 1980’s to provide a means for classifying the primary regions affected by dementia-producing illnesses, and to highlight behavioral features that may distinguish patients with cortical and subcortical disease.
“Cortical” dementia refers to a syndrome in which the patient presents with symptoms attributable to dysfunction of major domains of cognition. In these patients, memory impairment, language disturbances, disorders of visual recognition, or problems with complex skilled movement are prominent. Patients with Alzheimer’s disease, frontotemporal dementia, Creutzfeldt-Jacob disease, and Lewy-Body Dementia tend to present in this way. As such diseases progress, what may have begun as relatively mild problems in brain function can progress to severely impaired memory, inability to speak or conduct purposeful movement.
In “subcortical” dementias, cognitive problems are present but may not be as obvious or severe. Instead, the patient with subcortical dementia may more prominently display psychomotor slowing, problems initiating and maintaining activity, reduced motivation, and emotional symptoms such as apathy, indifference, or anhedonia. Word-finding problems or memory difficulties may be present, not from impairment in the cognitive domain itself, but from the patient’s inability to execute appropriate retrieval strategies needed to efficiently access information stored in the brain.
Patients with subcortical dementia may have prominent impairment in skills like planning and organization owing to the dense interconnections between subcortical structures and the frontal lobe, which is responsible for these functions. Diseases such as Parkinson’s disease and Huntington’s disease typically produce a “subcortical” picture.
The “cortical” vs. “subcortical” dementia distinction remains heuristic but is not without its detractors. Several well-controlled studies have failed to find quantitative neuropsychological differences between “cortical” and “subcortical” groups, while others have been more successful.
More important is the fact that many patients present with symptoms suggesting both cortical and subcortical damage. It is quite common, for example, for patients with behavioral and biomarker evidence of Alzheimer’s disease to also have extensive subcortical vascular disease, leading to a “mixed AD-vascular” picture. In these patients, the cortical-subcortical distinction may lose its utility, though it may still serve to remind the clinician to evaluate the full range of symptoms to determine whether the patient’s cognitive loss results from damage to cortical processors, impairment of subcortical systems regulating activation, motivation, and emotion, or both.
Source of graphic: Huntington’s Outreach Project for Education, at Stanford (HOPES)
Image Source: https://hopes.stanford.edu/dementia-in-huntingtons-disease/
