Parkinson's disease, or, more accurately, Parkinson's syndrome, was first described by J ames Parkinson in 1817, and little has been added to his description of the clinical features. Parkinson's syndrome is the most common motor disorder for which stereotactic surgery is used. Indeed, it was the availability of a large number of disabled Parkinson's syndrome patients that popularized stereotactic surgery. In the 1950s and 1960s, many patients presented for surgical management, since medical therapy was only marginally successful and since there was a large reservoir of patients with postencephalitic Parkinson's disease after the influenza epidemics three decades before.74 Activity in stereotactic treatments of Parkinson's syndrome waned as the pool of postencephalitic patients decreased, the patients who were candidates for surgery were already treated, and the introduction of L-dopa therapy provided symptomatic relief not previously possible.35 However, there is still a group of patients who are disabled by tremor and require stereotactic thalamotomy.The symptoms that give Parkinson's syndrome its classic appearance are tremor, rigidity, bradykinesia, and disturbance of postural adjustment. Although tremor is the most dramatic and characteristic symptom and may appear first, it is usually not the most disabling symptom, since it occurs at rest and may lessen or stop on intention. It has unmistakable characteristics that allow the immediate diagnosis of Parkinson's disease in that it is "pill-rolling" in nature, consisting of intermittent flex ion of the proximal fingers, thumb, or distal extremity at a frequency of 3 to 5 per second. A subtle tremor may be enhanced by vigorous activity or straining with the opposite hand or by holding the arm extended to the point of fatigue. The rigidity of Parkinson's syndrome is caused by a failure of muscle tone regulation, that is, the sustained simultaneous contraction of opposing muscles without hyper-reflexia. When passive stretch of the extremity is attempted, a distinct involuntary resistance, almost of a plastic nature, is felt. The resistance is greater at higher speeds of passive stretch. There is frequently a "cogwheel" sensation on testing for rigidity, which is believed to be the superimposition of tremor on rigidity. The rigidity may be sufficient to restrict superimposed voluntary movements and may consequently be disabling. However, it is bradykinesia that often causes the most disability. There is hesitation on initiating voluntary movement, which is then carried out with enforced slowness. Repetitive activities particularly are difficult, and both speed and excursion may decrease with each repetition. Bradykinesia contributes to the characteristic gait of parkinsonism and to the loss of postural reflexes. The subtle beginning of changes in postural reflexes may occur quite early, but it is not until other symptoms such as tremor appear that the diagnosis is made. If the patient lies supine and the head is suddenly allowed to drop back toward the surface of the examining table, it may remain suspended temporarily or indefinitely, a sensitive index of early changes in postural reflexes. Changes in postural reflexes cause the characteristic posture of Parkinson's patients-head thrust forward, shoulders rounded, arms bent at the elbows, and knees slightly flexed-and progressive kyphosis may herald the onset of the disease. The combination of bradykinesia and loss of postural reflexes causes a peculiar gait. There is significant delay in initiating walking, but, once started, the center of gravity may fall in front of the feet, so the patient must run faster and faster to catch up with the center of gravity. Sudden stopping is likewise impaired, with the center of gravity continuing to move, so that falling is common. The gait has a festinating quality, that is, short steps with small shuffling excursions that may be in slow motion. One early sign of the loss of postural reflexes is the loss of associated arm movements on walking, which adds to the characteristic Parkinson's gait. The combination of abnormal posture and gait allows the diagnosis of Parkinson's syndrome to be made from afar. The masklike facies o'f Parkinson's disease may also occur early. Automatic facial expression is lost. The patient appears to have a flat or depressed affect, which may not be appropriate to the patient's mood, even though many patients with Parkinson's syndrome suffer from severe depression. The skin adopts a waxlike' quality, which may be due to changes in the sweat glands. Speech becomes soft and mumbling( and there is loss of the modulation that ordinarily reflects emphasis or mood, so the speech attains a monotone quality. This may be a manifestation of bradykinesia of the muscles of speech. An occasional patient will have tremor of the mouth and tongue as well. In addition to speech disturbances, there may be difficulty with swallowing. Not only does this make eating a slow process, but the saliva may remain in the mouth or drooling may occur. There is some evidence that patients with Parkinson's syndrome have increased production of saliva, which may be diminished with many of the antiparkinson medications. Although mental changes may occur with arteriosclerotic parkinsonism, intellectual deterioration is ordinarily not a hallmark of Parkinson's syndrome. Symptoms classically begin in one hand or arm and progress in intensity as the other extremities become involved. Sometimes the disease can remain unilateral for a long period before there is evidence of involvement of the other side. The usual course, however, is for evidence of involvement of both sides to become apparent relatively early. The rate of progression can be variable. Many patients can go for years with only minor nondisabling symptoms, whereas others, particularly those with an onset at a young age, may progress to disability quite rapidly. Progression can be abruptly accelerated following injury, accident, or emotional stress. Generally, Parkinson's syndrome is divided into three types: arteriosclerotic, postencephalitic, and idiopathic. It is unusual to see a new case of the postencephalitic variety. The arteriosclerotic form occurs in older patients and is usually complicated by other diffuse neurological deficits. Most patients fall into the idiopathic category. There is a slight preponderance of males over females. Most patients have the onset of symptoms after the age of 50, but the disease may occur as early as age. At autopsy, a loss of pigmented cells of the zona compacta of the substantia nigra and of the locus ceruleus are seen.26 A classic finding in the idiopathic form is Lewy's inclusion bodies in the basal ganglia. Other pathologic changes are inconsistent and may relate to the age of the patient rather than the disease itself, nigra, where degeneration and depigmentation are seen on pathologic studies. This observation led logically to the treatment of Parkinson's disease by the administration of a precursor of dopamine. Since dopamine itself cannot cross the blood-brain barrier when administered orally, its precursor, L-dopa, was given in sufficient quantities to enter the brain, where it is converted into dopamine to correct the deficiency. Although the administration of L-dopa proved to be beneficial, especially for bradykinesia, the tolerated dose was limited because the conversion of L-dopa to dopamine throughout the body causes undesirable gastrointestinal and systemic side effects at low doses. In order to enhance the intracerebral level of dopamine without increasing the systemic dose, carbidopa was simultaneously administered. This drug blocks the conversion of dopa to dopamine throughout the body, but since it cannot cross the blood-brain barrier, it allows dopamine to be formed within the brain, so that higher more effective brain levels can be achieved. Despite the revolutionary improvement in the medical management of Parkinson's disease, disadvantages of long-term medical management have become apparent,33.39.45 especially in the more severe cases.4 Many patients do not tolerate medication at therapeutic doses, the tolerance to medication may diminish with time, or side effects such as dyskinesia or mental changes may interfere with continued L-dopa administration. In fact, in comparing patients treated with L-dopa early in the course of their disease with patients in whom medical therapy was withheld as long as possible, patients who were treated early were significantly more impaired in the long run, suggesting that some of the deterioration may be due to the L-dopa therapy itself rather than to the Parkinson's syndrome
The indications for stereotactic surgery in Parkinson's syndrome changed with the advent of L-dopa therapy, and they are changing once again as the difficulties with long-term L-dopa management become apparent. Of the symptoms thus far described, tremor responds best to stereotactic thalamotomy, rigidity next, and bradykinesia least.74 On the other hand, bradykinesia responds best to L-dopa treatment, rigidity next, and tremor least,84 which is the order in which these symptoms cause disability and, coincidentally, the reverse of the order in which they respond to thalamotomy. Consequently, medical management has become the first priority in the treatment of most patients with Parkinson's syndrome. If tremor is the most disabling symptom, thalamotomy should be considered if the patient does not respond promptly to a brief trial of medical management (Fig. 431-4). If the tremor is only partially alleviated by surgery, medical therapy should be resumed postoperatively, ,since the combination of medical and surgical therapy may be optimal in some patients.50.79 If the tremor is symmetrical, the dominant side might be operated upon first to give the patient the maximum rehabilitation from a unilateral procedure. If lesions are made bilaterally, they should be asymmetric, if possible, to minimize the risk of side effects to mentation or speech, and a minimum of 6 to 12 weeks should elapse before the second operation. If bradykinesia is the most serious problem, once the patient does not respond to medication or becomes intolerant to the medication and is still significantly disabled stereotactic pallidotomy should be considered. Stereotactic pallidotomy (production of lesions in the globus pallidus) was used early in the history of stereotaxis, but was largely abandoned because of the more dramatic alleviation of tremor seen after thalamotomy and because it had achieved inconsistent results.73 Newer imaging techniques have made lesion placement more accurate, and a slight modification of the target within the pallidum has led to a resurgence of interest in this target.44 Considerable improvement has been noted in both bradykinesia and rigidity after production of lesions in the ventroposterolateral part of the pallidum interna. Stereotactic surgery for Parkinson's disease involves interruption of the extrapyramidal pathways in Fore!' s field, in the ventrolateral nucleus of the thalamus, or in the globus pallidus. Lesions correctly placed in the posterior part of the ventrolateral nucleus of the thalamus (V.im in Hassler's nomenclature) are most effective against tremor, whereas interruption of the anterior portion may have a better effect on rigidity.29 There is some evidence that interruption of the pallidothalamic connections is optimal for the improvement of rigidity and bradykinesia. Most series report satisfactory relief of tremor in 85 to 93 percent of well-selected thalamotomy patients and improvement of rigidity and bradykinesia in 50 percent or more.43,77.79.80 Improvement is more often apparent in the upper extremity; truncal symptoms or postural symptoms may not be improved even with bilateral surgery. The muscle cramping associated with rigidity is often relieved. Micrographia may be relieved and associated movements may return.Neurological complications are usually transient and mild,39.43 but significant complications may occur in 4 to 6 percent, usually involving changes in equilibrium, speech, or mentation.I3,50.55.83 Mortality is 0 to I percent,43,50 so the risk of stereotactic surgery compares favorably with the risk of medical management.2I.39.77,80 The risk increases over the age of 60 and definitely over the age of 65. The risk in hypertensive patients is particularly acute, and surgery should be considered only reluctantly in patients who have mental deterioration.