Subcortical dementias includes those diseases which predominantly affects the

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...

along with features of cognitive decline. Diseases such as

progressive supranuclear palsy Progressive supranuclear palsy (PSP) is a late-onset degenerative disease involving the gradual deterioration and death of specific volumes of the brain. The condition leads to symptoms including loss of balance, slowing of movement, difficulty ...

Huntington's chorea Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unst ...

and

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

are different in many features from the other cortical dementias like Alzheimer's disease. Yet these patients present clinically with mild forgetfulness and slowed thought process along with abnormal movements and problems with motility.

Clinical features

Clinically subcortical dementia usually is seen with features like slowness of mental processing, forgetfulness, impaired cognition, lack of initiative-apathy, depressive symptoms (such as

anhedonia Anhedonia is a diverse array of deficits in hedonic function, including reduced motivation or ability to experience pleasure. While earlier definitions emphasized the inability to experience pleasure, anhedonia is currently used by researchers ...

, negative thoughts, loss of self-esteem and

dysphoria Dysphoria (; ) is a profound state of unease or dissatisfaction. It is the semantic opposite of euphoria. In a psychiatric context, dysphoria may accompany depression, anxiety, or agitation. In psychiatry Intense states of distress and uneas ...

), loss of social skills along with extrapyramidal features like

tremor A tremor is an involuntary, somewhat rhythmic, muscle contraction and relaxation involving oscillations or twitching movements of one or more body parts. It is the most common of all involuntary movements and can affect the hands, arms, eyes, f ...

s and abnormal movements. In most of the patients with

Huntington's disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an uns ...

s 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 Leukodystrophies are a group of usually inherited disorders characterized by degeneration of the white matter in the brain. The word ''leukodystrophy'' comes from the Greek roots ''leuko'', "white", ''dys'', "abnormal" and ''troph'', "growth". ...

" also causes subcortical dementia with prominent frontal 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 The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...

. Such patients have prominent

apraxia Apraxia is a motor disorder caused by damage to the brain (specifically the posterior parietal cortex or corpus callosum), which causes difficulty with motor planning to perform tasks or movements. The nature of the damage determines the disor ...

and

agnosia Agnosia is the inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually ...

. 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 fibrillary 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 The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direction ...

, and rostral

brain-stem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is ...

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 (especially empathy), extrapyramidal functions, and visuospatial skills. Additionally, damage to the

basal forebrain Part of the human brain, the basal forebrain structures are located in the forebrain to the front of and below the striatum. They include the ventral basal ganglia (including nucleus accumbens and ventral pallidum), nucleus basalis, diagonal ba ...

can cause

amnesia Amnesia is a deficit in memory caused by brain damage or disease,Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company. but it can also be caused temporarily by the use ...

and psychotic disorders.

Controversy

One of the problems with the concept of subcortical dementia is the fact that name implies that it is due to lesions confined to subcortical structures. Anatomically none of the neurodegenerative dementias are strictly cortical or subcortical. In fact, there is 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.

Examples

Progressive supranuclear palsy Progressive supranuclear palsy (PSP) is a late-onset degenerative disease involving the gradual deterioration and death of specific volumes of the brain. The condition leads to symptoms including loss of balance, slowing of movement, difficulty ...

(chronic

acetogenin Acetogenins are a class of polyketide natural products found in plants of the family Annonaceae. They are characterized by linear 32- or 34-carbon chains containing oxygenated functional groups including hydroxyls, ketones, epoxides, tetrahydr ...

poisoning) * Atypical Parkinsonism *

Binswanger disease Binswanger's disease, also known as subcortical leukoencephalopathy and subcortical arteriosclerotic encephalopathy, is a form of small-vessel vascular dementia caused by damage to the white brain matter. White matter atrophy can be caused by many ...

(and other forms of

vascular dementia Vascular dementia (VaD) is dementia caused by problems in the supply of blood to the brain, typically a series of minor strokes, leading to worsening cognitive abilities, the decline occurring piecemeal. The term refers to a syndrome consisting ...

) *

Corticobasal degeneration Corticobasal degeneration (CBD) is a rare neurodegenerative disease involving the cerebral cortex and the basal ganglia. CBD symptoms typically begin in people from 50 to 70 years of age, and the average disease duration is six years. It is chara ...

Huntington disease Huntington's disease (HD), also known as Huntington's chorea, is a neurodegenerative disease that is mostly inherited. The earliest symptoms are often subtle problems with mood or mental abilities. A general lack of coordination and an unst ...

Multiple system atrophy Multiple system atrophy (MSA) is a rare neurodegenerative disorder characterized by autonomic dysfunction, tremors, slow movement, muscle rigidity, and postural instability (collectively known as parkinsonism) and ataxia. This is caused by p ...

HIV-associated neurocognitive disorder (HAND) HIV-associated neurocognitive disorders (HAND) are neurological disorders associated with HIV infection and AIDS. It is a syndrome of progressive deterioration of memory, cognition, behavior, and motor function in HIV-infected individuals during ...

* HIV-associated dementia

References

Cognitive disorders Mental disorders due to brain damage Dementia Learning disabilities Aging-associated diseases {{nervoussystem-disease-stub