Parkinsonism: Early Manifestations

IDIOPATHIC PARKINSON DISEASE

Idiopathic Parkinson disease is characterized by the presence of tremor, rigidity, or bradykinesia early in the course of the illness, with postural and/or gait disturbances usually developing late in the course of the disease. The presence of atypical symptoms and the rate of progression of the disease are important in distinguishing Parkinson disease from other parkinsonian syndromes. For example, early-onset postural instability, falls, and gait disturbances characterize progressive supranuclear palsy (PSP); marked autonomic disturbances, such as erectile dysfunction in men or urinary bladder incontinence in women may herald the onset of multiple system atrophy (MSA). Stooping, a masked facies, decreased blinking, micrographia, and hypophonia, are common features of parkinsonism but are not unique to Parkinson disease and may be present in other parkinsonian syndromes. Severe anterocollis and camptocormia (bent spine) are more likely to be due to MSA or paraspinalis muscle fatty atrophy/myopathy rather than Parkinson disease (see Plate 7-5). Excessive neck rigidity, primarily when accompanied by marked oculomotor disturbances, such as hypometric slowed saccades in downward gaze or a clear defect of voluntary ocular excursion to command or pursuit but a normal excursion on the doll’s eye maneuver, particularly in the vertical plane, suggest PSP. Other oculomotor disturbances, such as saccadic intrusions (principally square wave jerks or ocular flutter), nystagmus, or ocular impersistence, may be present in PSP, MSA, corticobasal degeneration (CBD), Huntington disease (HD), and the cerebellar ataxias in variable combinations and degrees of severity.

It is estimated that approximately 80% of the dopaminergic neurons in the substantia nigra have been lost by the time that Parkinson disease is first diagnosed; hence the initial degenerative process leading to parkinsonism begins several years before the clinical diagnosis. Although it is usually difficult to diagnose Parkinson disease in the preclinical (premotor) stage, anosmia, constipation, and mood and personality changes may precede the onset of motor symptoms by a few years. For most patients, the onset of motor symptoms is subtle and may be obvious first to family members or coworkers.

Dopamine deficiency is responsible for the pathophysiology of motor symptoms in Parkinson disease. Although symptoms improve with dopaminergic replacement therapy, tremor and postural and gait disturbances tend to have only a partial response to treatment, particularly in the later stages of the disease, suggesting the substrate of such symptoms may lie somewhere else along the central nervous system. Indeed, it has been shown that the pedunculopontine nuclei (PPN), a cholinergic structure closely linked to the striatonigral system, may play a major role in gait control. In addition, preliminary studies using PPNtargeted neuromodulation have shown mild improvements in gait difficulties and freezing in some patients, although the final outcomes in such studies are unclear at this time.

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