Parkinson’s Disease (PD) is a multifactorial, progressively degenerative neurologic disease that affects over 1 million people in North America alone. Specifically in Canada, this affects over 84,000 Canadians, with an estimated incidence of around 55 per 100,000 population. The average age of diagnosis in Canada is 66 years, and is typically seen in individuals over 40. It is mainly characterized by degeneration of dopaminergic cells in the substantia nigra, however, there is also degeneration of pigmented nuclei in the brainstem, spinal cord, cortex and gut.
Clinically, PD is characterized mainly by 4 cardinal features: tremor, bradykinesia, rigidity, and postural instability as the disease progresses. In addition, there may be other motor manifestations including but not limited to: craniofacial (masked facies, speech impairment, sialorrhea), visual (blurred vision, impaired upward gaze), musculoskeletal (stooped posture, kyphosis), gait (shuffling, freezing, destination). Although originally described as a motor system disorder, there are diverse non-motor clinical features, including but not limited to: olfactory dysfunction, fatigue, sleep disturbances, mood disorders including depression and anxiety, gastrointestinal dysfunction, etc. The features can be bilateral, and are usually asymmetric.
Initially, the disease process is very subtle and findings may only be seen on MRI; as the disease progresses, there may be a minor, generalized loss of cerebral volume.
On T1 imaging, iron accumulation may lead to a mild hyper intensity of the red nuclei, as well as the pars compacta and pars reticulata in the substantia nigra. Also, the depigmentation of the substantia nigra in PD may manifest as a loss of normal slight hyper intensity in the substantia nigra.
On T2/SWI weighted imaging, there is normally a swallow tail sign that is a hyper intense signal due to a cluster of dopaminergic cells collectively called nigrosome-1. In PD however, this normal swallow tail sign appearance within the posterior third of the substantia nigra is lost. This has been shown to have diagnostic accuracy of over 90% for PD and dementia with Lewy-bodies. Furthermore, the loss of pigmented neutrons may result in a lack of normal susceptibility signal drop-out of the substantia nigra and red nuclei, with minor spots of hyperintensity in the pars compacta. Iron accumulation may possibly lead to a confluence of the normal hypointense regions of the substantia nigra.
References:
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2. https://www150.statcan.gc.ca/n1/pub/82-003-x/2014011/article/14112-eng.htm
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