Approach Considerations
No single imaging technique is necessary or sufficient for diagnosis of Huntington disease (HD). Measurement of the bicaudate diameter (ie, the distance between the heads of the 2 caudate nuclei) by CT scan or MRI is a reliable marker of HD. [10]
Abnormalities in positron emission tomography (PET) scanning and proton MR spectroscopy have been reported; however, their use in clinical practice is limited.
Genetic testing (reported as the CAG repeat number for each allele) is now commercially available.
Genetic testing may not be necessary in a patient with a typical clinical picture and a genetically proven family history of HD.
In the absence of a family history of HD, patients with a suggestive clinical presentation should undergo genetic testing to exclude or confirm HD.
Persons at risk for HD who request presymptomatic testing should undergo extensive genetic counseling and neurologic and psychiatric evaluation, given the implications of receiving a positive (or negative) result for an untreatable, familial, progressive, neurodegenerative disease. Most testing centers follow strict protocols, such as the one put forth by the Huntington's Disease Society of America (HDSA). [15]
If the genetic test is negative for HD, then testing for systemic lupus erythematosus (SLE), antiphospholipid antibody syndrome, thyroid disease, neuroacanthocytosis, DRPLA, Wilson disease, and other less common causes of chorea may be reasonable, depending on the individual case.
Staging
The extent of gross striatal pathology, neuronal loss, and gliosis provides a basis for grading the severity of HD pathology (grades 0-4). See Pathophysiology.
