Corticobasal degeneration

Corticobasal degeneration (CBD) is an uncommon neurodegenerative disease and is one of the subset of tauopathies.

Terminology

Corticobasal syndrome (CBS) represents the clinical syndrome that is diagnosed clinically, while corticobasal degeneration is only reserved for the subset of cases that are pathologically confirmed as the tauopathy ⁶. The corticobasal syndrome has causes in addition to corticobasal degeneration, including progressive supranuclear palsy (PSP-CBS), frontotemporal dementia, posterior cortical atrophy variant of Alzheimer disease, and Creutzfeld-Jakob disease⁷.

Epidemiology

The vast majority of cases are sporadic, although a number of familial cases have been described ². Patients are usually in the fifth to seventh decades of life ⁵, with the youngest reported case being 40 years of age ³.

Clinical presentation

Due to its myriad presentations whichCorticobasal degeneration has a heterogenous clinical presentation, often crossover with other neurodegenerative conditions, corticobasal degeneration ismaking it challenging to diagnose ⁵.

The classical "corticobasalcorticobasal syndrome" is a progressive disorder with various asymmetric movement abnormalities, myoclonus, as well as cortical signs including ideomotor apraxia and alien limb phenomenon ⁵. Corticobasal syndrome represents the clinical syndrome of the pathologically confirmed corticobasal degeneration. Despite extensive efforts in developing diagnostic criteriaHowever, clinical diagnosis does not always correlate with the pathological diagnosis.

In thethere is a broader spectrum of corticobasal syndromephenotype, patients often present with slowly progressive symptoms and signs including ^1,2:

• akinetic-rigid syndrome, usually beginning in one limb, which unlike in Parkinson disease is not ameliorated by levodopa ¹
• limb apraxia
• limb dystonia
• myoclonic jerkslimb myoclonus
• postural instability and falls
• cognitive impairment, often with pronounced frontal lobe signs ²
• cortical sensory loss
• alien limb phenomenon ^1,2,4

Pathology

The characteristic histopathological findings are neuronal loss and numerous "ballooned" achromatic neurones ¹. Although these features are seen throughout the brain, certain regions are more severely affected. They include:

• frontoparietal cortex
• subcortical structures
  • striatum
  • substantia nigra

Radiographic features

MRI is the modality of choice for assessing corticobasal degeneration, although similar findings can, only to a certain degree, be seen on CT.

MRI

Typical findings include ^1,2:

• asymmetric cortical atrophy
  • superior parietal lobule: most constant feature
  • peri-Rolandic gyri
    • precentral gyri
    • postcentral gyri
  • superior frontal gyri
• bilateral atrophy of the basal ganglia
• atrophy of the corpus callosum ²
• T2 hyperintensity
  • subcortical white matter of affected gyri
  • posterolateral putamen

The pattern of atrophy in corticobasal degeneration may be distinguishable from that of progressive supranuclear palsy. Patients with corticobasal degeneration tend to have atrophy in posterolateral and medial frontal cortical regions, but relatively preserved brainstem anatomy ⁵.

Research is ongoing regarding the use of techniques such as 3D volumetric MRI and diffusion tensor imaging ⁵.

Nuclear medicine

SPECT and PET studies tend to demonstrate hypometabolism in the superior parietal and superior frontal areas, as well as (but less frequently) in the basal ganglia and thalamus ^2,5. Early metabolic changes tend to be asymmetrical similar to the clinical presentation. 

Treatment and prognosis

There are no current drug therapies available to modify the course of corticobasal degeneration. Treatment is often focussed on symptomatic relief. Supportive services such as speech and occupational therapy should not be overlooked ⁵. 

Unfortunately, the overall prognosis is poor, with patients demonstrating gradual neurological decline. Death occurs typically 5 to 10 years after the diagnosis is first made ³.

Differential diagnosis

Clinically there is overlap with other conditions, some of which also cause corticobasal syndrome ^1,7:

• multiple system atrophy (MSA)
• Parkinson disease
• progressive supranuclear palsy (PSP)
• Pick disease
• progressive subcortical gliosis
• posterior cortical atrophy