Huntington's Disease

Clinical Evaluation

Although predictive genetic tests may indicate whether individuals carry the disease gene, these tests are not able to confirm the onset of the disorder. Therefore, the diagnosis of HD is also based on a thorough clinical evaluation including a complete physical and neurologic assessment; detection of characteristic symptoms and findings (e.g., chorea, emotional and behavioral disturbances, progressive dementia, etc.); as well as a careful patient and family history. Neurologic assessment may include testing to evaluate cognitive status, reflexes, balance, and movement, including evaluation of certain voluntary eye movements necessary in focusing on moving targets (i.e., saccades). If a symptomatic individual is gene negative, diagnostic studies may be conducted to eliminate other neurodegenerative disorders that have similar symptoms including chorea (e.g., neuroacanthocytosis, dentatorubropallidoluysian atrophy, Wilson disease, etc.). Such studies may include certain blood tests, neurophysiologic tests, and neuroimaging techniques.

Specialized brain imaging studies may also provide evidence that supports a diagnosis of HD. For example, in moderately advanced cases, computerized tomography (CT) scanning demonstrates characteristic bilateral neurodegeneration of the caudate nuclei and the putamen as well as associated neuronal loss within the temporal and frontal lobes of the cerebral cortex. According to some reports, magnetic resonance imaging (MRI) may be more sensitive, potentially detecting putamen atrophy before obvious neurodegeneration within the caudate nuclei. CT scanning may also detect characteristic enlargement of cavities of the brain (ventricles). In addition, positron emission tomography (PET) scanning may show decreased glucose and oxygen metabolism within the caudate nuclei. Although such findings may also be associated with other neurodegenerative disorders, they may be helpful in supporting a suspected diagnosis of HD when associated with characteristic clinical findings and family history. In general, neuroimaging is performed only if a symptomatic individual does not have the HD gene and there is a suspicion of another neurodegenerative disorder.