Clinically sub cortical dementia usually is seen with features like slowness of mental processing, forgetfulness, impaired cognition, lack of initiative-apathy, depressive symptoms, loss of social skills along with extrapyramidal features like tremors and abnormal movements. In most of the patients with Huntington's diseases the first clinical feature to appear is the change in personality.The dementia is more severe in patients with early onset of Huntington's disease. Parkinson's disease is characterised by features of dementia in older age.The adult type “leukodystrophy” also causes subcortical dementia with prominentfrontal lobe features. As a general rule the earliest symptoms in "cortical" dementia include difficulty with high-level behaviors such as memory, language, problem-solving and reasoning, mathematics and abstract thoughts – functions associated with the cerebral cortex.Such patients have prominent apraxia and agnosia. However, in "subcortical" dementia these high-level behaviours are less affected.
Pathophysiology
In most common types of dementias there is widespread degeneration in the cerebral cortex – such as the plaques and neuro fibrillation tangles which are the hallmark of Alzheimer's disease. In subcortical dementia, there is targeted damage to regions lying under the cortex. The pathological process that result in subcortical dementia shows neuronal changes that involve primarily the thalamus, basal ganglia, and rostral brain-stem nuclei and mostly, some projections in the white matter from these regions to the cortex, with relative sparing of the cerebral cortex. It affects arousal, attention, mood, motivation, language, memory, abstraction, social skills, extrapyramidal functions, and visuospatial skills. Additionally, damage to the basal forebrain can cause amnesia and psychotic disorders.
Controversy
One of the problems with the concept of sub cortical dementia is the fact that name implies that it is due to lesions confined to sub cortical structures.Anatomically none of the neurodegenerative dementias are strictly cortical or subcortical. In fact, there's invariably an overlap of both cortical and subcortical neuronal changes in both types.
History
Charcot described dementia as a feature in Parkinson's disease.McHugh introduced the concept of subcortical dementia. Mayeux and Stern and their colleagues and Tierney and coworkers have been critical of the concept of subcortical dementia.
