Parkinson's disease belongs to a group of conditions called movement disorders. It is characterized by muscle rigidity, tremor, a slowing of physical movement (bradykinesia) and a loss of physical movement (akinesia) in extreme cases. The primary symptoms are the results of decreased stimulation of the motor cortex by the basal ganglia, normally caused by the insufficient formation and action of dopamine, which is produced in the dopaminergic neurons of the brain. Secondary symptoms may include high level cognitive dysfunction and subtle language problems. PD is both chronic and progressive.
PD is the most common cause of chronic progressive parkinsonism, a term which refers to the syndrome of tremor, rigidity, bradykinesia and postural instability. PD is also called "primary parkinsonism" or "idiopathic PD" (classically meaning having no known cause although this term is not strictly true in light of the plethora of newly discovered genetic mutations). While many forms of parkinsonism are "idiopathic", "secondary" cases may result from toxicity most notably of drugs, head trauma, or other medical disorders.
The term Parkinsonism is used for symptoms of tremor, stiffness, and slowing of movement caused by loss of dopamine. "Parkinson's disease" is the synonym of "primary parkinsonism", i.e. isolated parkinsonism due to a neurodegenerative process without any secondary systemic cause. In some cases, it would be inaccurate to say that the cause is "unknown", because a small proportion is caused by genetic mutations. It is possible for a patient to be initially diagnosed with Parkinson's disease but then to develop additional features, requiring revision of the diagnosis.[2]
There are other disorders that are called Parkinson-plus diseases. These include: multiple system atrophy (MSA), progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Some include dementia with Lewy bodies (DLB) ¡ª while idiopathic Parkinson's disease patients also have Lewy bodies in their brain tissue, the distribution is denser and more widespread in DLB. Even so, the relationship between Parkinson disease, Parkinson disease with dementia (PDD), and dementia with Lewy bodies (DLB) might be most accurately conceptualized as a spectrum, with a discrete area of overlap between each of the three disorders. The cholinesterase inhibiting medications have shown preliminary efficacy in treating the cognitive, psychiatric, and behavioral aspects of the disease of both PD and DLB. The natural history and role of Lewy bodies is little understood.
These Parkinson-plus diseases may progress quicker than typical idiopathic Parkinson disease. If cognitive dysfunction occurs before or very early in the course of the movement disorder then DLBD may be suspected. Early postural instability with minimal tremor especially in the context of ophthalmoparesis should suggest PSP. Early autonomic dysfunction including erectile dysfunction and syncope may suggest MSA. The presence of extreme asymmetry with patchy cortical cognitive defects such as dysphasia and apraxias especially with "alien limb" phenomena should suggest CBD.
The usual anti-Parkinson's medications are typically either less effective or completely ineffective in controlling symptoms; patients may be exquisitely sensitive to neuroleptic medications like haloperidol, so correct differential diagnosis is important.
Essential tremor may be mistaken for Parkinson's disease but lacks all other features besides tremor, and has particular characteristics distinguishing it from Parkinson's disease, such as improvement with beta blockers and alcoholic beverages.[1]
Wilson's disease (hereditary copper accumulation) may present with parkinsonian features; young patients presenting with parkinsonism or any other movement disorder are frequently screened for this rare condition, because it may respond to medical treatment. Typical tests are liver function, slit lamp examination for Kayser-Fleischer rings, and serum ceruloplasmin levels.
