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INTRODUCTION

CLINICAL FEATURES

Parkinsonism is a general term used to define a symptom complex manifest by bradykinesia (slowness of voluntary movements) with rigidity and/or tremor; it has a wide differential diagnosis (Table 195-1). Parkinson's disease (PD) is idiopathic parkinsonism without evidence of more widespread neurologic involvement. PD afflicts >1 million individuals in the United States. Peak age of onset in the 60s; course progressive over 10–25 years. Tremor ("pill rolling" of hands) at rest (4–6 Hz). Presentation with tremor confined to one limb or one side of body is common. Other findings: rigidity ("cogwheeling"—increased ratchet-like resistance to passive limb movements), bradykinesia, fixed expressionless face (facial masking) with reduced frequency of blinking, hypophonic voice, drooling, impaired rapid alternating movements, micrographia (small handwriting), reduced arm swing, and flexed "stooped" posture with walking, shuffling gait, difficulty initiating or stopping walking, en-bloc turning (multiple small steps required to turn), retropulsion (tendency to fall backwards). Nonmotor aspects of PD include depression and anxiety, cognitive impairment, sleep disturbances, sensation of inner restlessness, loss of smell (anosmia), and disturbances of autonomic function. Normal muscular strength, deep tendon reflexes, and sensory exam. Diagnosis based on history and examination; neuroimaging, EEG, and CSF studies usually normal for age.

TABLE 195-1DIFFERENTIAL DIAGNOSIS OF PARKINSONISM

PATHOPHYSIOLOGY

Most PD cases occur sporadically and are of unknown cause. Degeneration of pigmented pars compacta neurons of the substantia nigra in the midbrain resulting in lack of dopaminergic input to striatum; accumulation of cytoplasmic intraneural inclusion granules (Lewy bodies). Cause of cell death is unknown, but it may result from generation of free radicals and oxidative stress; no environmental factor has yet been conclusively determined to cause PD. Rare genetic forms of parkinsonism exist (~5% of cases); most common are mutations in α-synuclein or parkin genes. Early age of onset suggests a possible genetic cause of PD, although one genetic form (LLRK2) causes PD in the same age range as sporadic PD and may be responsible for as much as 1% of all sporadic cases. Mutations in the glucocerebrosidase (GBA) gene are also associated with an increased risk of idiopathic PD.

DIFFERENTIAL DIAGNOSIS

Atypical parkinsonism refers to a group of neurodegenerative conditions that usually are associated with more widespread neurodegeneration than is found ...

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