Parkinson's disease is by far the most common cause of the parkinsonian syndrome, accounting for approximately 80% of cases (the remainder being due to other neurodegenerative disease, such as Lewy body dementia) 1.
The most common form is encountered in elderly patients and is common, seen in 2-4% of all individuals older than 65 years of age.
A juvenile form of Parkinson's disease is also recognised, manifesting between 20 - 40 years of age 1.
The majority of cases (85 - 90%) are sporadic, however 10 - 15% of patients have a positive family history 1.
Parkinson's disease is classically characterised by a triad of features:
- resting tremor
- postural instability : sometimes added as a cardinal feature 3
Dementia can be a late feature. When present it is known as Parkinson's disease with later developing dementia (PDD). In contrast, Lewy body dementia has cognitive impairment either preceding or at most within 12 months of clinical onset of parkinsonian symptoms 2.
The dopaminergic tract is predominantly affected in Parkinson's disease, and histologically, it is characterised by degeneration of the substantia nigra as well as a number of other regions including parts of the basal ganglia, brainstem, autonomic nervous system and cerebral cortex 3.
At least eleven genes have been implicated in various forms of Parkinson's disease 3. Interestingly depending on which genes are involved, various clinical features are more or less prominent (e.g. Kufor-Rakeb syndrome).
Even more interestingly not all mutations result in Lewy bodies. For example juvenile Parkinson's disease has been linked to mutations in the PARK2 gene, which encodes for the enzyme ubiquitin ligase-L3. In normal individuals, ubiquitin ligase-L3 is involved in ubiquitination of alpha-synuclein (the main component of Lewy bodies) and allows the formation of Lewy bodies. In patients with juvenile Parkinson's disease its function is impaired and the formation of Lewy bodies is impossible. This finding suggests that Lewy bodies cannot be thought of as synonymous with, and causative of Parkinson's disease. Perhaps even Lewy bodies play a protective role other forms of Parkinson's disease, which manifests 20-40 years later 1.
Initial imaging findings are subtle and only potentially seen on MRI.
With advanced disease, non-specific generalised minor cerebral volume loss can be demonstrated.
MRI is not only able to identify some relatively specific features, but more importantly is often able to identify features which suggest secondary parkinsonism (e.g. extensive small vessel ischaemic change).
Features of Parkinson's disease include 1:
T2* (GE / SWI) : loss of normal susceptibility signal drop-out of the substantia nigra and red nuclei
- best sign
- due to loss of melanin containing neurons
Treatment and prognosis
The mainstay of treatment is medical. In patients with refractory symptoms, deep brain stimulation may be useful.
Parkinson's disease was first described by a British physician James Parkinson, both in himself and five patients 1. As such it is one case where the apostrophe is recommended.
There is significant overlap between many neurodegenerative disease, and Parkinson's disease is no exception. Clinically the differential includes 1,3:
dementia with Lewy bodies
- dementia is clinically evident before, concurrently or at most within 12 months of onset of parkinsonian symptoms 2
- multiple system atrophy (MSA)
- progressive supranuclear palsy (PSP)
- cerebrovascular disease
metabolic diseases with parkinsonian signs and symptoms : basal ganglia signal abnormalities are usually more pronounced 1.
- Wilson disease
- manganese toxicity
- chronic hepatitis
- 1. Kornienko VN, Pronin IN. Diagnostic Neuroradiology. Springer Verlag. (2008) ISBN:3540756523. Read it at Google Books - Find it at Amazon
- 2. Harding AJ, Broe GA, Halliday GM. Visual hallucinations in Lewy body disease relate to Lewy bodies in the temporal lobe. Brain. 2002;125 (Pt): 391-403. doi:10.1093/brain/awf033 - Pubmed citation
- 3. Dekker MC, Bonifati V, Van duijn CM. Parkinson's disease: piecing together a genetic jigsaw. Brain. 2003;126 (Pt): 1722-33. doi:10.1093/brain/awg172 - Pubmed citation
Synonyms & Alternative Spellings
|Synonyms or Alternative Spelling||Include in Listings?|
|Parkinson disease (PD)||✗|
|Parkinson's disease (PD)||✗|