Evidence for more widespread cerebral pathology in early HD: an MRI-based morphometric analysis

Using advances in neuroimaging to detect, understand, and monitor disease progression in Huntington's disease

Transgenic mouse models and other screens are being used to identify potential therapeutic agents for use in clinical trials in Huntington's disease (HD). The development of surrogate markers that can be used in clinical therapeutics is an active area of research. Because HD is relatively uncommon and only a portion of available subjects meet inclusion and exclusion criteria, therapeutic trials are limited by the availability of potential subjects as well as the relative insensitivity of the clinical measures used. Neuroimaging methods offer the potential to provide noninvasive, reproducible, and objective methods not only to better understand the disease process but also to follow in clinical studies to determine if a drug is effective in slowing down disease progression or perhaps even in delaying onset. Following is a review of the literature, which highlights the studies that have been published to date.

Global cerebral atrophy in early stages of Huntington's disease: quantitative MRI study

Global brain atrophy was determined in 70 patients suffering from Huntington's disease (HD) and 70 healthy controls, using brain parenchymal fractions calculated from 3D MRI data in a standardized procedure. In HD patients, brain parenchymal fractions were significantly reduced compared to controls in all age groups; the physiological decline with age was less pronounced in HD. However, brain parenchymal fraction values did not allow the prediction of clinical impairment (as assessed by clinical scores). Global brain parenchyma reduction seems to be an early or even constitutional feature of HD, but clinical symptoms appear to reflect regional rather than global atrophy. Overall, MRI-based brain volume quantification correlated with clinical scores clarifies the functional impact of morphological brain alterations.

The basal ganglia and inhibitory mechanisms in response selection: evidence from subliminal priming of motor responses in Parkinson's disease

Subliminal response priming was used to investigate inhibitory control processes relevant to response selection impairments in Parkinson's disease. Using a backward masking technique, covert activation of left- or right-hand responses was induced without subjects consciously perceiving the stimuli (right- or left-pointing arrows). The masked priming stimuli were followed by visible arrow stimuli, instructing for a left- or right-hand response, at a delay (interstimulus interval, ISI) of 0 or 100 ms. Motor cortex activation was recorded by means of the electroencephalographic lateralized readiness potential (LRP). Parkinson's disease patients (n = 12) were compared with age-matched controls (n = 12) and young controls (n = 10). In young controls, the ISI = 100 ms task effectively invoked inhibition of the subliminally primed responses, as demonstrated by a reversal of prime-target compatibility effects compared with the ISI = 0 ms task. This reversal implied that there was a so-called negative compatibility effect with faster responses and fewer errors when prime and target arrows pointed in opposite directions than when they required the same response. This negative compatibility effect turned into a positive compatibility effect in Parkinson's disease patients, while age-matched controls produced intermediate values. Together, these results support the view that response selection involves competitive, mutually inhibitory interactions between response alternatives, influenced by basal ganglia-thalamocortical mechanisms. As indicated by the reduced inhibition of partially activated responses, Parkinson's disease and, to a lesser degree, normal ageing affect the efficiency of these inhibitory interactions.

Looking Backward to Move Forward: Early Detection of Neurodegenerative Disorders

Early detection of neurodegenerative disorders would provide clues to the underlying pathobiology of these diseases and would enable more effective diagnosis and treatment of patients. Recent advances in molecular neuroscience have begun to provide the tools to detect diseases like Alzheimer's disease, Parkinson's disease, and others early in their course and potentially even before the development of clinical manifestations of disease. These genetic, imaging, clinical, and biochemical tools are being validated in a number of studies. Early detection of these slowly progressive diseases offers the promise of presymptomatic diagnosis and, ultimately, of disease-modifying medications for use early in disease and during the presymptomatic period.