PARKINSON DISEASE or Parkinson ’s disease (PD, IPD) was described by Sir James Parkinson in 1836. His description was so accurate that it has stood the test of time.
A patient with PD has difficulties in performing actions. He is slow (BRADYKINESIA) in all his activities, including standing, walking, dressing, eating, etc. His limbs are rigid (RIGIDITY), stiff and board-like. In addition, he has a PARKINSONIAN TREMOR – a coarse, shaking of the limb, especially the hand, which becomes prominent when the limb is by the side of the body and not engaged in some action (REST TREMOR). The Parkinsonian Tremor becomes nearly invisible when the patient is using the limb for some action, and disappears altogether during sleep.
Apart from these 3 central features, most people with PD eventually develop a POSTURAL INSTABILITY – an inability to balance themselves while standing or even sitting, and a tendency to fall with the slightest push.
There are other features peculiar to this condition, but the most important of these are summarized here:
- PD usually starts in the 5th or 6th decade (40 to 60 years of age)
- PD usually starts on one side of the body; even after many years, after it has progressed to involve both sides of the body, it still remains more prominent on the side in which it started.
- PD responds very well to certain specific anti-Parkinsonian medications; lack of a significant response to these drugs is in fact used as a criterion to rule-out PD
- PD can cause urinary retention, but rarely urinary incontinence
- About 30% patients with PD develop dementia or significant cognitive decline; 70% maintain normal cognition till the end
The diagnosis of PD is based on its clinical features. Commercially available CT and MRI scans serve only to rule out other conditions which it may mimic in its early stages. 18-FluoroDeoxyGlucose-PET (18F-FDG-PET) if available can be helpful to confirm the diagnosis, especially in uncertain situations.
PD is a progressive disorder; the progression may be very gradual. It is common for PD patients to survive for up to 2 decades. Initially, the response to drugs is very good. In the 3rd or 4th year, or sometimes earlier, after the medications have been used consistently for some years – patients of PD start to develop some problems which are peculiar to their situation. The most common and important of these is an abnormal and excessive movement of limbs – called Dyskinesia.
PD patients also develop another problem called the “ON-and-OFF” phenomenon. In this situation, the patient still responds well to the medications, but the drug effect wears off much faster than before. The patient fluctuates from an ON stage when the drug effect is present, to an OFF stage when the effect has worn off, in a matter of minutes. This can be very disconcerting, and forces them to avoid most activities.
Despite these problems, PD patients prefer to remain on the drugs; various methods and modifications to the drugs have been tested and marketed to improve the situation for patients with such complications.
In the later stages of the illness, the effect of the drugs is barely perceptible. Patients may become bed-ridden at this stage, and this can lead to various complications and even death.
Various surgical treatments are available for patients with such late-stage complications. The oldest and best known is STEREOTACTIC THALAMOTOMY, in which a carefully placed lesion in the THALAMIC NUCLEUS on each side produces significant relief of Parkinsonian Tremor. A similar lesion in the SUB-THALAMIC NUCLEUS produces an even better effect in reducing ALL the symptoms of PD.
The draw-back with such “lesion surgery” is the inability to control the effect – it produces a permanent effect which cannot be modified. If during the surgery there is a slight damage to a neighboring structure – though this is rare – the patient can develop some complication like HEMIPLEGIA.
To improve the situation, a newer technique – available since about 2 decades – is DEEP BRAIN STIMULATION (DBS), which involves implantation of electrodes into the same nuclei, with wires connecting them to a battery-operated pacemaker. The pacemaker can be implanted under the skin on the chest, and can be powered on or off at will. Even the frequency of stimulation can be modified, producing, in fact, a highly controlled and measured effect over whichever nucleus is chosen for the procedure. DBS of Sub-Thalamic Nucleus is presently the best treatment for PD.
Some patients have received spectacular benefits from DBS; others have seen a return of drug effectiveness without the crippling ON-OFF effect or the troubling Dyskinesias. In all these situations, the patient’s life is much improved, mobility restored and maintained much longer, and the inevitable bed-bound state may be delayed by a decade or longer.
PARKINSONISM AND PARKINSON DISEASE
The principle symptoms of PD – slowness/bradykinesia, Rigidity, and Tremor – are referred to as PARKINSONISM. PD is ONE of the causes of Parkinsonian symptoms; there are many other less common entities in which Parkinsonism may be a central or a peripheral feature. The condition labeled PROGRESSIVE SUPRANUCLEAR PALSY (PSP) is an example.
PD differs from these other causes of Parkinsonism in being less severe, slower in progression, and more responsive to medications. Most of these conditions do not respond to anti-Parkinsonian medications, or may respond in a minor way. Some of these conditions can be lethal; for example, PSP can lead to death in about 10 years.