Corticobasal syndrome (CBS) is a progressive neurological disorder that may involve the motor system, cognition or both. Classically, it begins as a movement disorder, with affected individuals showing a unilateral (one sided) paucity of movement and muscle rigidity with a tremor. This may result in the patient first being diagnosed as having Parkinson’s disease. Strength remains normal but the limb becomes progressively less useful because of the problems with tone, slowness, tremor and praxis. A sign called “apraxia,” or loss of praxis, describes a disconnection between the thought and the action despite adequate strength to complete that action.
Patients with CBS are easier to diagnose if they are showing apraxia, such as no longer being able to use the remote control for the television set, or not being able to retrieve mail from the mailbox. Initial symptoms of CBS often begin around age 60 (although there is variability in the age of onset) and become bilateral as the disease progresses. A patient with CBS may first present with a language disorder and develop the motor symptoms over time.
The term corticobasal degeneration (CBD) is applied to cases which have a particular type of tauopathy at autopsy (detailed below). Some cases of CBS prove to have Alzheimer’s pathology instead.
Key Clinical Features
Motor symptoms of CBD are similar to those found in Parkinson disease, such as:
- Akinesia/bradykinesia – an absence or slowness of movements; lack of spontaneous movements
- Rigidity -a resistance to imposed movement
- Tremor, often complex
- Limb dystonia – abnormal posture of the extremities
These cognitive symptoms may be associated with CBD (though not all are seen in all patients):
- Alien hand syndrome in which the patient does not recognize the actions of his hand and can’t control movement of the hand or arm;
- Apraxia – the loss of the ability to make familiar, purposeful movements, manifested as difficulty using familiar objects or doing familiar things. Examples include using utensils, combing one’s hair, and dressing;
- Acalculia – difficulty carrying out simple calculations, such as adding and subtracting.
- Visual-spatial impairment – an individual with corticobasal degeneration may have difficulty orienting objects in space.
Language symptoms including hesitant and halting speech (progressive aphasia), are seen in some patients.
A CBS patient may begin with any of the three types of signs above: cognitive, motor or language. Development of a second and/or third category of signs makes it easier for the physician to recognize the illness as CBS.
Key Pathologic Features
Upon autopsy, the brain tissue of corticobasal degeneration (CBD) patients is characterized by nerve cell loss, gliosis and atrophy (shrinkage) of the deeper layers in the posterior frontal and/or parietal lobes, and the substantia nigra. Swollen (ballooned) nerve cells containing tau and phosphorylated neurofilament epitopes, similar to those seen in Pick’s disease, are a hallmark feature.
Scientists have recently determined that affected CBD brain cells contain deposits of abnormal forms of the protein tau. Tau is present in all neurons, and it plays important roles in the structure and function (metabolism) of neurons. But in CBD, tau is abnormally phosphorylated, and this biochemical change keeps it from functioning properly.
CBD is almost always sporadic, developing by chance rather than being inherited. Some research has found associations with CBD and a specific form (variant) of the tau gene. However, this information is not useful for the diagnosis of specific individuals because the tau forms are neither sensitive nor specific for this degeneration.
There is no treatment available to slow the course of corticobasal degeneration, and the symptoms of the disease are generally resistant to therapy. Drugs used to treat Parkinson disease-type symptoms are sometimes tried, but often do not produce significant or sustained improvement for motor symptoms.
Some CBD patients benefit from the selective serotonin reuptake inhibitors (SSRIs) used in treating depression and/or the acetylcholinesterase inhibitors used in Alzheimer disease, which enhance the activity of neurotransmitters in the brain. Clinicians may also employ antioxidants, such as vitamin E or coenzyme Q10, which are known to slow the progression of damage to brain cells in general. Medications may also be prescribed to diminish the tremor.
Maintaining a healthy lifestyle with physical and mental activity is generally recommended for patients with central nervous system degenerative diseases, as is a “heart healthy” diet.
Although there is no treatment for CBD, therapy does help to manage the symptoms, and hopefully one day we will be able to delay their progression. Occupational and physical therapies provide passive range of motion in affected muscles, and help prevent contractures (paralysis of a muscle in the tense state) in rigid limbs. Speech therapy may help delay the progression of language symptoms.
It is important for caregivers and families to think about long-term management issues and identify a team of experts who can help with difficult medical, financial and emotional challenges. It is imperative to have a physician who is knowledgeable about frontotemporal degeneration and CBD. Other medical specialists who may be helpful include: speech therapists, occupational and physical therapists, neuropsychologists, nurses (especially home-care nursing), and genetic counselors.
Corticobasal degeneration usually progresses slowly over the course of 6 to 8 years. During this time, the patient’s ability to live and function independently is diminished, leaving them dependent on others for activities of daily living.
Death in CBD is generally caused by pneumonia or other complications, such as sepsis (an infection throughout the body) or pulmonary embolism (a blood clot that blocks a major blood vessel in the lung).
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