Corticobasal degeneration.

Corticobasal degeneration (CBD) is a neurodegenerative disorder characterized clinically by a combination of cortical and basal ganglia signs. Pathologically, it is classified as a tauopathy. The most distinctive clinical feature is its unilateral or markedly asymmetric presentation; among parkinsonian syndromes, with rare exceptions, only Parkinson's disease presents with such asymmetry. The most common presenting cortical features include apraxia (patients often complain of a "useless" limb), aphasia (usually nonfluent), parietal lobe sensory signs (agraphesthesia, extinction, astereognosis), frontal dementia, or myoclonus. Basal ganglia signs include rigidity, akinesia, limb dystonia, and postural instability. The diagnosis is often challenging for three reasons: 1) The full complement of findings are rarely seen at presentation; 2) If CBD is not suspected, subtle but relevant findings (eg, extinction, language impairment, myoclonus, or apraxia) may not be searched for or appreciated; 3) The clinical picture of CBD has substantial overlap with a variety of other parkinsonian and dementing illnesses. The differential diagnosis includes Parkinson's disease, progressive supranuclear palsy, frontotemporal dementia, primary progressive aphasia, and Alzheimer's disease. The clinical diagnosis is not confirmed pathologically in up to half of cases, so the term corticobasal syndrome is often preferred during life, reserving the term corticobasal degeneration for pathologically verified cases. Treatment of CBD is primarily supportive, and most patients die within 10 years of onset. Parkinsonian signs may improve to a modest degree with levodopa, clonazepam can suppress myoclonus, and botulinum toxin can relieve dystonia. Early speech therapy, physical therapy, and occupational therapy, as well as assist devices such as a rolling walker may improve functioning and reduce complications such as aspiration pneumonia and falls. With time, however, most patients lose their independence and mobility. Throughout the course of the illness (particularly when it is advanced), caring for the caregiver is as important as caring for the patient.