Parkinson’s Disease or Paralysis agitans is a degenerative disorder of the central nervous system. The motor symptoms of Parkinson’s disease result from the death of dopamine-generating cells in the substantia nigra, a region of the midbrain; the cause of this cell death is unknown. Early in the course of the disease, the most obvious symptoms are movement-related; these include shaking, rigidity, slowness of movement and difficulty with walking and gait. Later, cognitive and behavioural problems may arise, with dementia commonly occurring in the advanced stages of the disease. Other symptoms include sensory, sleep and emotional problems. PD is more common in the elderly, with most cases occurring after the age of 50.
The main motor symptoms are collectively called parkinsonism, or a “parkinsonian syndrome”. Parkinson’s disease is often defined as a parkinsonian syndrome that is idiopathic (having no known cause), although some atypical cases have a genetic origin. Many risk and protective factors have been investigated: the clearest evidence is for an increased risk of PD in people exposed to certain pesticides and a reduced risk in tobacco smokers. The pathology of the disease is characterized by the accumulation of a protein called alpha-synuclein into inclusions called Lewy bodies in neurons, and from insufficient formation and activity of dopamine produced in certain neurons within parts of the midbrain. Lewy bodies are the pathological hallmark of the idiopathic disorder, and the distribution of the Lewy bodies throughout the Parkinsonian brain varies from one individual to another. The anatomical distribution of the Lewy bodies is often directly related to the expression and degree of the clinical symptoms of each individual. Diagnosis of typical cases is mainly based on symptoms, with tests such as neuroimaging being used for confirmation.
Modern treatments are effective at managing the early motor symptoms of the disease, mainly through the use of levodopa and dopamine agonists. As the disease progresses and dopaminergic neurons continue to be lost, a point eventually arrives at which these drugs become ineffective at treating the symptoms and at the same time produce a complication called dyskinesia, marked by involuntary writhing movements. Diet and some forms of rehabilitation have shown some effectiveness at alleviating symptoms. Surgery and deep brain stimulation have been used to reduce motor symptoms as a last resort in severe cases where drugs are ineffective. Research directions include investigations into new animal models of the disease and of the potential usefulness of gene therapy, stem cell transplants and neuroprotective agents. Medications to treat non-movement-related symptoms of PD, such as sleep disturbances and emotional problems, also exist.
The disease is named after the English doctor James Parkinson,
SIGNS AND SYMPTOMS
Parkinson’s disease affects movement, producing motor symptoms. Non-motor symptoms, which include autonomic dysfunction, neuropsychiatric problems (mood, cognition, behavior or thought alterations), and sensory and sleep difficulties, are also common
DIAGNOSIS
There is no lab test that will clearly identify the disease, but brain scans are sometimes used to rule out disorders that could give rise to similar symptoms. Patients may be given levodopa and resulting relief of motor impairment tends to confirm diagnosis. The finding of Lewy bodies in the midbrain on autopsy is usually considered proof that the patient suffered from Parkinson’s disease. The progress of the illness over time may reveal it is not Parkinson’s disease, and some authorities recommend that the diagnosis be periodically reviewed Other causes that can secondarily produce a parkinsonian syndrome are Alzheimer’s disease, multiple cerebral infarction and drug-induced parkinsonism.Parkinson plus syndromes such as progressive supranuclear palsy and multiple system atrophy must be ruled out.Anti-Parkinson’s medications are typically less effective at controlling symptoms in Parkinson plus syndromes. Faster progression rates, early cognitive dysfunction or postural instability, minimal tremor or symmetry at onset may indicate a Parkinson plus disease rather than PD itself . Genetic forms are usually classified as PD, although the terms familial Parkinson’s disease and familial parkinsonism are used for disease entities with an autosomal dominant or recessive pattern of inheritance.Medical organizations have created diagnostic criteria to ease and standardize the diagnostic process, especially in the early stages of the disease. The most widely known criteria come from the UK Parkinson’s Disease Society Brain Bank and the US National Institute of Neurological Disorders and Stroke The PD Society Brain Bank criteria require slowness of movement (bradykinesia) plus either rigidity, resting tremor, or postural instability. Other possible causes for these symptoms need to be ruled out. Finally, three or more of the following features are required during onset or evolution: unilateral onset, tremor at rest, progression in time, asymmetry of motor symptoms, response to levodopa for at least five years, clinical course of at least ten years and appearance of dyskinesias induced by the intake of excessive levodopa Accuracy of diagnostic criteria evaluated at autopsy is 75–90%, with specialists such as neurologists having the highest rates
Computed tomography (CT) and magnetic resonance imaging (MRI) brain scans of people with PD usually appear normal.[32] These techniques are nevertheless useful to rule out other diseases that can be secondary causes of parkinsonism, such as basal ganglia tumors, vascular pathology and hydrocephalus.[32] A specific technique of MRI, diffusion MRI, has been reported to be useful at discriminating between typical and atypical parkinsonism, although its exact diagnostic value is still under investigation. Dopaminergic function in the basal ganglia can be measured with different PET and SPECT radiotracers. Examples are ioflupane (trade name DaTSCAN) and iometopane (Dopascan) for SPECT or fluorodeoxyglucose (18F) for PET. A pattern of reduced dopaminergic activity in the basal ganglia can aid in diagnosing PD.
TREATMENT
Repetitive transcranial magnetic stimulation temporarily improves levodopa-induced dyskinesias Its usefulness in PD is an open research topic although recent studies have shown no effect by rTMS. Several nutrients have been proposed as possible treatments; however there is no evidence that vitamins or food additives improve symptoms. There is no evidence to substantiate that acupuncture and practice of Qigong, or T’ai chi, have any effect on the course of the disease or symptoms. Further research on the viability of Tai chi for balance or motor skills are necessary. Fava beans and velvet beans are natural sources of levodopa and are eaten by many people with PD. While they have shown some effectiveness in clinical trials their intake is not free of risks. Life-threatening adverse reactions have been described, such as the neuroleptic malignant syndrome.
Aejaz Iqbal (Microbiologist) can be reached at aijazsmile@gmail.com
