Home > Diagnosis, Types of dementia > What is Corticobasal Degeneration?

What is Corticobasal Degeneration?

Corticobasal Degeneration (CBD), or Corticobasal Ganglionic Degeneration (CBGD), is a rare progressive neurodegenerative disease.  It involves the loss of nerve cells, as well as atrophy (shrinkage) of the cerebral cortex and basal ganglia, and is characterized by serious difficulties with cognitive and motor function.  Symptoms can present as similar to Parkinson’s disease and progressive supranuclear palsy, which can make diagnosis difficult.

CBD is a relatively new diagnosis, with the first three patients identified in 1968.  These patients were originally described as having “corticodentatonigral degeneration with neuronal achromasia” and “cortical basal ganglionic degeneration.”  The cause is unknown, but it occurs as a result of damage to the basal ganglia.  In particular, it is characterized by neuronal depigmentation, or loss of melanin in a neuron, in the substantia nigra.  Persons diagnosed with CBD also exhibit an assymetrical atrophy of the frontal and parietal ares of the brain.  At autopsy, their brains often show ballooning of neurons, hypertrophy of glial cells, and aggregation of tau proteins.

Typically, a person is not diagnosed with CBD until about the age of 60,  however can be as young as 28.  It is predominantly a disease of women, although not exclusively so.  Prevalence of the disease is estimated at 4.9 to 7.3 per 100,000 people.  Most of those diagnosed with CBD reach mortality within six to eight years, although some have been known to live for 13 years and beyond.  The primary cause of death is aspiration pneumonia related to dysphagia, although pneumonia and other infections, as well as pulmonary embolisms, are also common.  Speech problems are common, as is incontinence related to the person’s inability to express a need to go to the bathroom.  Psychiatric and cognitive difficulties, although present, are much less problematic than other forms of dementia.

Some of the most profound symptoms of CBD involve motor functioning, and these are often the first signs that the person is ill.  Initially, symptoms often appear unilaterally (on one side of the body), and then develop bilaterally as the disease progresses.  The most commonly observed features include parkinsonism, alien hand syndrome, apraxia, and aphasia.  Parkinsonism in CBD is typically present in one arm, rather than in both.  The characteristic signs of parkinsonism (rigidity, bradykinesia, and gait disorder) are seen in CBD as well.  One study showed that within three years after diagnosis, over 70% of those with CBD exhibited bradykinesia.

Approximately 60% of those diagnosed with CBD exhibit alien hand syndrome.  This is a peculiar disorder in which the person appears not to recognize his hand as belonging to him, and has difficulty controlling its movements.  One particular form of alien hand syndrome is often seen in CBD, wherein the patient’s hand actively follows the hand of someone else with whom he is in direct contact.

The particular form of apraxia often present in CBD, ideomotor apraxia, is often seen in concert with bradykinesia and rigidity.  Basically, the person is unable to repeat or to mimic certain movements, either with or without the use of objects.  These people may have trouble initiating walking, and may appear as if their feet are glued to the floor, leading to stumbling and balance difficulties.  This disorder is primarily associated with deterioration in the premotor cortex, parietal association areas, connecting white matter tracts, thalamus, and basal ganglia.  Some individuals with CBD also exhibit limb-kinetic apraxia, which affects fine movements of the hands and fingers.

The form of aphasia typically seen in those with CBD tends to be of the non-fluent variety.  These individuals have difficulty initiating speech.  They may omit words, and show disconnected speech.  Eventually, as the disease progresses, they often lose the ability to speak at all.

Psychiatric and cognitive symptoms of CBD include depression, dementia, and irritability.  The presence of dementia can lead to a confusion with Alzheimer’s disease or another related disorder.

Neuroimaging techniques do not, as yet, provide a definitive diagnosis of CBD.  Fluorodopa positron emission tomography (Fdopa PET) can be used to study the efficacy of the dopamine pathway.  MRI images can be used to identify areas of cortical atrophy in the brain, and the identification of assymetric involvement, can be used to suggest the presence of the disease.  However, this needs to be verified with the use of other assessments. The use of functional MRI, with simple finger motor tasks, can also suggest CBD through lower levels of activity in the parietal cortex, sensorimotor cortex, and supplementary motor cortex.

Since the exact cause of CBD is unknown, there is no specific treatment for the disease.  Currently, treatment focuses on amelioration of symptoms.  For instance, the parkinsonism characteristic of the disease responds favorably to dopaminergic drugs, with moderate relief of symptoms.  Clonazepam may provide some relief for the myoclonus.  Other treatments tend to be supportive or palliative, including speech and occupational therapy, feeding strategies, and wheelchairs.




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