Corticobasal Degeneration - Causes, Symptoms, Complications, and Management

Introduction

Corticobasal degeneration (CBD) is a rare neurological (brain) disorder that primarily affects the cerebral cortex and basal ganglia, resulting in progressive cellular degeneration and deterioration. Initially, it was categorized as a motor disease. Later studies showed that cognitive and behavioral symptoms are also present. The condition usually starts as a movement disorder affecting a single limb (arm or leg) and later involves all four limbs. The patient presents with symptoms like muscle rigidity, speech difficulties, poor coordination, and memory loss.

The exact cause is unknown. CBD is also referred to as cortical basal ganglionic degeneration.

How Common Is the Condition?

CBD is categorized as a rare neurological disease. The prevalence of the condition is 5 in 100000 in the general population. Approximately about one new case is reported every year among 100,000 people. About four to six percent of people with Parkinsonism have CBD. CBD usually affects the old aged (50-70 years). The average age of onset is 64 years. Females are more affected than males. No cases were reported under 40 years of age.

What Are the Causes of Corticobasal Degeneration?

The exact etiology is unknown. Different factors are linked to the development of CBD. These factors include genetics, aging, and environmental changes. CBD is characterized by progressive degeneration and deterioration of brain tissue. This leads to the loss of nerve cells in specific brain regions. As a result of this nerve loss, certain lobes of the brain undergo atrophy (shrinkage). The most affected brain parts include:

• Cerebral Cortex - Nerve tissue layer that envelopes the brain. This part is concerned with memory functions, voluntary movement, learning, and coordination of sensory information.

• Basal Ganglia- Part of the brain involved in motor and learning functions.

Tau Protein

• Some studies have shown a relationship between tau protein and the development of CBD. Tau is a specific normal protein found in brain cells that helps in nutrient transportation.

• Abnormal levels of tau protein accumulation within brain cells characterize CBD. This abnormal accumulation leads to the deterioration of brain tissue. Hyperphosphorylation (attachment of phosphate group) of tau protein is seen in CBD; this destabilizes nutrient transportation.

• Abnormal tau protein accumulation is also seen in other disorders like Alzheimer’s disease, Niemann- Pick disease type C, progressive supranuclear palsy, and some cases of Parkinsonism. These disorders are generally referred to as ‘tauopathies.’

What Are the Signs and Symptoms of Corticobasal Degeneration?

The term ‘corticobasal syndrome’ is used to indicate the clinical diagnosis. The presentation of symptoms, their severity, and progression varies from person to person. The first clinical manifestation is usually muscle rigidity/stiffness associated with one of the limbs. Individuals are not able to make voluntary movements with the affected limb. In most cases, arms are affected first. Initially, the condition is unilateral, affecting one side, and afterward progresses to both sides affecting all four limbs.

The symptoms include the following:

• Difficulty in movement coordination.

• Unable to control movement.

• Postural tremor (shaking while in a particular position).

• Action tremor (shaking while performing a task).

• Rest tremor (shaking while at rest position).

• Bradykinesia (exaggerated slowness of movement).

• Brief involuntary muscle spasms.

• Postural instability (balance is affected).

• Communication difficulties.

• Speech difficulties.

• Difficulty in counting (difficulty with numbers).

• Dysphagia (swallowing difficulties).

• Uncoordinated walk (ataxia).

• Inability to control eyelid blinking.

• Dementia (loss of intellectual ability).

• Memory loss.

• Irritability.

• Poor attention span.

• Obsessive-compulsive behavior.

What Are the Diagnostic Tests For Corticobasal Degeneration?

The diagnosis is mainly based on clinical symptoms. It is important to rule out other similar conditions like Parkinsonism, Alzheimer’s disease, stroke, etc. There is no specific test for the condition; the common tests done include:

• MRI Scan (Magnetic Resonance Imaging) - MRI tests use a powerful magnetic field and radio waves to form detailed brain images. MRI helps in detecting the atrophic areas of the brain.

• PET Scan (Positron Emission Tomography) - PET scan is a type of functional imaging technique that uses a radioactive tracer to get three-dimensional images of the brain. It helps in detecting brain activity.

• DaTscan (Dopamine Transporter Scan) - DaTscan is a diagnostic test used for detecting dopaminergic neurons. They are mostly used for the diagnosis of Parkinsonism.

These diagnostic tests help in ruling out other similar conditions like Parkinsonism, brain tumor, stroke, Alzheimer’s disease, etc. Sometimes there is a chance that CBD is misdiagnosed as Parkinsonism. In such case doctor prescribes Levodopa, but the condition will not become better. Another test carried out is neuropsychological testing. Neuropsychological testing involves a series of memory tests using pictures and words. The test assesses the following:

• Concentration span.

• Memory.

• Numbers and counting.

• Language understanding.

• Processing of visual information (pictures and words).

Persons with CBD will have a poor attention span, memory loss, difficulty with numbers, language difficulties, and problems with processing visual information.

What Are the Complications of Corticobasal Degeneration?

As the condition progress, at a later stage, the patient may become bedridden. In such cases, there is a chance for life-threatening complications like pneumonia, bacterial infection, sepsis, and pulmonary embolism.

How Can Corticobasal Degeneration Be Managed?

There is no definitive treatment for the condition. Treatment to prevent or slow down the disease progression is also not available. But, the quality of life of the affected can be improved and the condition can be managed. The management of CBD involves a multidisciplinary approach and includes the following members:

• Neurologist.

• Physiotherapist.

• Occupational therapist.

• Speech and language therapist.

• Social worker.

• Nurse (neurology specialty).

• Dietician.

• Symptomatic treatment is done, in which medicines are given to treat symptoms like muscle stiffness, pain, anxiety, memory loss, etc. Baclofen is used to treat muscle rigidity. Benzodiazepine and Clonazepam are used to treat muscle spasm. Cholinesterase inhibitors are used to treat memory problems.

• Cognitive stimulation therapy is used for overcoming dementia symptoms.

• Physiotherapy under the guidance of a physiotherapist involves exercises that help to improve posture, reduce muscle stiffness and increase muscle strength.

• Speech therapy helps with speech and language problems.

• A dietician will provide the diet to be followed; it will be a balanced diet and easier to swallow. If swallowing difficulty is severe, a feeding tube is required.

• Palliative care aims at providing spiritual, social, and psychological support.

• The patient may require an assistive device like a walker or cane for walking.

Conclusion

CBD is a rare neurological disease with no specific treatment. Initially, the condition is unilateral and progresses to affect all four limbs. The person also experiences cognitive and behavioral symptoms like dementia, memory loss, speech difficulty, difficulty with numbers, etc. The symptoms worsen as the condition progress. But a multidisciplinary approach involving the neurologist, physiotherapist, social worker, nurse, speech therapist, dietician, and occupational therapist can improve the quality of life of the affected.