Corticobasal degeneration (CBD)
Corticobasal degeneration (CBD) is extremely rare and manifests as very asymmetric (often unilateral) parkinsonism with rigidity, apraxia (trouble coordinating the limb to accomplish a task), myoclonus (muscle jerks), dystonia, and rarely a condition known as alien limb syndrome, where the limb has complex movements of its own accord.
CBD is a different condition pathologically than Parkinson’s disease (PD); it is known as a tauopathy, meaning that the tau protein misfolds and causes disruption of neuron function, whereas in PD the abnormal protein is called alpha-synuclein. CBD is typically accompanied by dementia. The speech may be halting or hesitant and swallowing problems are common. Unfortunately, CBD can progress more rapidly than typical (idiopathic) PD, and patients typically lose the ability to walk or care for themselves within a few years of the onset of symptoms.
The diagnosis is primarily clinical but functional imaging such as FDG-PET can elucidate the patterns of metabolic dysfunction seen in CBD. Research is being done to develop imaging that directly measures tau protein deposition, which will enable more specific and accurate diagnosis.
Treatment is limited. Medications for dementia and parkinsonism are often given but are typically of low benefit. There are small studies that are enrolling to modify the tau protein but are in very early stages.