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Corticobasal degeneration (CBD) is a rare neurodegenerative disease, classified as a form of adult-onset parkinsonism, often presenting with unilateral arm rigidity, dystonia, and cognitive decline. It is increasingly recognized as part of the spectrum of frontotemporal lobar degeneration.
About
- Also known as Corticobasal ganglia degeneration (CBGD) .
- Characterized by a combination of movement disorder, cognitive dysfunction, and language impairment, often with the hallmark alien limb phenomenon (where a limb seems to act independently of the person’s control).
- Classified as a tauopathy, sharing pathological features with other disorders like progressive supranuclear palsy (PSP) and frontotemporal dementia (FTD).
Aetiology
- A tauopathy : Accumulation of tau protein in neurons and glia, leading to neurodegeneration.
- Involves multiple brain regions:
- Nigrostriatal tracts.
- Subcortical structures including the thalamus, subthalamic nuclei, pallidum, red nucleus, and dentate nucleus.
- Pathological changes such as large, pale, ballooned neurons are seen in the basal ganglia.
Clinical Features
- Unilateral parkinsonism : Initially presents on one side with rigidity, bradykinesia, and tremors (although tremors are less common than in idiopathic Parkinson’s disease).
- Alien limb phenomenon : An arm or leg moves involuntarily, performing complex movements without conscious control.
- Dystonia : Involuntary muscle contractions, typically in the affected limb, leading to abnormal postures. The hand often assumes a dystonic posture with wrist and thumb flexed into the palm.
- Myoclonus : Sudden, brief, involuntary muscle jerks, especially in the arms and legs.
- Supranuclear gaze palsy : Difficulty with voluntary eye movements, especially in horizontal and vertical directions, similar to progressive supranuclear palsy (PSP).
- Cognitive and speech issues :
- Aphasia : Difficulty with speech production or comprehension (often progressive non-fluent aphasia).
- Dysphasia : Impairment of language ability, affecting communication.
- Apraxia : Difficulty in performing purposeful movements, even though the desire and physical ability to do so are intact.
- Dementia : Progressive cognitive decline with memory, reasoning, and personality changes.
- Behavioral changes including disinhibition, depression, and emotional blunting.
- Asymmetrical presentation of motor symptoms is common, progressing over time to affect both sides.
- Additional signs: postural instability, falls, dysphagia, and sensory deficits.
Investigations
- Blood tests : FBC, U&E, ESR, CRP, LFT, TFT, B12, folate to exclude metabolic and systemic causes.
- Imaging :
- MRI : Shows asymmetric frontoparietal cortical atrophy (particularly contralateral to the affected side). Cortical thinning and enlarged sulci in parietal and frontal lobes may also be seen.
- PET scan : Reduced fluorodopa uptake in the basal ganglia. FDG-PET may show asymmetric hypometabolism, particularly in the parietal lobe.
- DaTscan (SPECT) : May help distinguish between corticobasal degeneration and other causes of parkinsonism.
- Neuropsychological tests : Can assess cognitive function and identify deficits in memory, language, and executive function.
- Genetic testing may be performed if there is suspicion of other neurodegenerative diseases (though CBD is not typically genetic).
Management
- Supportive care is the cornerstone of management, with an interdisciplinary approach involving neurologists, physiotherapists, speech therapists, and occupational therapists to help maintain function and independence.
- Medications :
- L-Dopa : Response to levodopa is usually poor or transient, unlike idiopathic Parkinson’s disease.
- Quetiapine or other antipsychotics may be used to manage behavioral symptoms such as agitation or delusions, but regular reviews are necessary to minimize cognitive side effects.
- Dystonia treatments : Clonazepam, valproate, baclofen, or botulinum toxin may help with dystonic postures and movements, though these treatments should be used cautiously to avoid cognitive side effects.
- Selective serotonin reuptake inhibitors (SSRIs) may be used to manage depression.
- Physiotherapy and regular exercise programs can help maintain mobility and reduce rigidity.
- Speech therapy is important for managing dysphasia and swallowing difficulties, and PEG tubes may be needed in severe cases of dysphagia.
- End-of-life care planning is crucial, focusing on quality of life, symptom management, and addressing dysphagia, immobility, and cognitive decline.
Prognosis
- The disease progresses slowly but steadily, leading to significant disability.
- Median survival is approximately 6-8 years after symptom onset, though progression varies between individuals.
- Death typically results from complications such as pneumonia, infections, or immobility-related issues.