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A combination of movement disorders and mental, emotional, or behavioral changes can be caused by several different conditions. Of course, HD is considered first in a person with a known family history. A person having any such combination of symptoms will probably be referred to a specialist in disorders of the brain and nervous system (neurologist).

The neurologist will ask many questions about the symptoms and how they started, other medical problems now and in the past, family medical history, medications, work and travel history, and habits and lifestyle. A detailed physical examination will include tests of movement and sensation, coordination, balance, reflexes and other nervous system functions, and mental status. The main goals of the medical interview and examination are to inventory the exact disabilities and to rule out other conditions that can cause similar symptoms.

Lab tests

These tests are used to confirm the diagnosis of HD and dementia.

• DNA repeat expansion: The test identifies the HD mutation. It uses a technique called PCR to measure the number of CAG repeats in the HD gene. This test is very accurate in confirming the disease, because no other similar disease has the gene mutation.
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• Homovanillic acid: Homovanillic acid is a product of the neurotransmitter dopamine, which plays an important role in movement. The amount of homovanillic acid in the cerebrospinal fluid is lower in people with HD than in healthy people. Cerebrospinal fluid is a clear fluid that surrounds and helps protect the brain and spinal cord. The degree of reduction in homovanillic acid level is a marker of the severity of dementia and life expectancy in HD. A sample of the fluid is obtained for this test by lumbar puncture (spinal tap). This procedure involves using a hollow needle to pierce the space around the spinal cord in the lower back.

Imaging studies

Brain scans can be useful in measuring the extent of brain damage in the disease.

• CT scan or magnetic resonance imaging (MRI) of the brain shows atrophy (shrinkage) of the parts of the brain affected by HD.
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• Single-photon emission computed tomography (SPECT) scan shows changes in metabolism and blood flow in the parts of the brain affected by HD.
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• Position-emission tomography (PET) scan shows changes in brain function that often occur before symptoms begin in HD. This scan is available only in a few large medical centers. Its usefulness in HD is still being studied.

Neuropsychological testing

No medical test definitively confirms cognitive decline or dementia in HD. The most accurate way to measure cognitive decline is through neuropsychological testing.

• The testing involves answering questions and performing tasks that have been carefully designed for this purpose. It is carried out by a specially trained psychologist.
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• Neuropsychological testing addresses the individual’s appearance, mood, anxiety level, and experience of delusions or hallucinations.
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• It assesses cognitive abilities such as memory, attention, orientation to time and place, use of language, and abilities to carry out various tasks and follow instructions.
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• Reasoning, abstract thinking, and problem solving are tested.
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• Neuropsychological testing gives a more accurate diagnosis of the problems and thus can help in treatment planning.
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• The first test results are used as a baseline for measuring changes in cognitive abilities. The tests may be repeated periodically to see how well treatment is working and to check for new problems.