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Essential tremor (ET) is one of the most common movement disorders. Although often considered a monosymptomatic disorder (postural and kinetic tremor), ET has more recently been considered a more heterogeneous syndrome, with motor and nonmotor features. The diagnosis is clinical and pharmacologic and surgical therapies exist. ET is frequently misdiagnosed as Parkinson disease or dystonia. The traditional notion of ET as a benign disorder has been challenged by those who view ET as a slowly progressive neurodegenerative disorder.

Multiple system atrophy (MSA) is an adult-onset, progressive, neurodegenerative condition that has several different initial presentations. Ultimately affected patients develop parkinsonian features, autonomic dysfunction, cerebellar ataxia, and corticospinal deficits. Patients with MSA are often misdiagnosed as having Parkinson disease. This article discusses the epidemiology and pathophysiology of MSA, in addition to addressing clinical and diagnostic signs and symptoms, and the limited treatment options available to physicians.

The diagnosis of Parkinson's disease remains a clinical diagnosis with no confirmatory laboratory or imaging studies available. The classic diagnostic criteria include 2 of 3 cardinal motor features of parkinsonism (resting tremor, cogwheel rigidity, and bradykinesia) on examination. Interest in a "premotor diagnosis" of Parkinson's disease is based on the hope that neuroprotective therapy could be initiated earlier and affect disease course. However, there is no proven method to diagnose Parkinson's disease prior to the onset of motor signs and there is no proven neuroprotective treatment. Once the diagnosis is made, the neurologist must decide, with the patient, whether to institute treatment at the time of diagnosis or whether to institute treatment when functional disability evolves. There are multiple possible initial pharmacologic choices for the initial treatment of Parkinson's disease, including monoamine oxidase type B inhibitors, dopamine receptor agonists, and levodopa/carbidopa.

Since progressive supranuclear palsy (PSP) was first reported as a separate clinicopathological entity in 1964, hundreds of other cases have been recorded, and PSP is now one of the most common atypical Parkinson-plus disorders. Diagnostic criteria have been developed by the National Institute of Neurological Disorders and Stroke and the Society for PSP, Inc. Because there is no biological marker for PSP, definitive diagnosis depends on neuropathological examination. Characteristics of PSP include gait disturbances, supranuclear ophthalmoplegia, axial limb rigidity, and frontal lobe dysfunction. Although there are no treatments that alter the natural history of disease in PSP and no drugs that provide significant symptomatic benefits, several supportive measures are available.

Parkinson's disease is characterized by progressive slowness in activities of daily living and is the most common cause of parkinsonism, whose symptoms include resting tremor, cogwheel rigidity, and bradykinesia. The introduction of levodopa and its positive effect on motor dysfunction in Parkinson's disease has allowed neurologists to focus on motor fluctuations. "End-of-dose wearing-off" and "morning akinesia" are terms to describe the transition between a patient's relatively normal motor performance when levodopa is effective and when it has transiently lost its effect on motor responses and parkinsonian symptoms reemerge. The choices available to alleviate these motor fluctuations range from altering the patient's levodopa/carbidopa dosing schedule to the addition of other agents to the regimen, including dopamine receptor agonists, catechol-O-methyltransferase inhibitors, monoamine oxidase inhibitors, and amantadine, as well as implementing dietary changes. Therapeutic decisions can be difficult because older agents have not been compared in head-to-head trials to determine which drugs are better than others and the order in which they should be tried or added to the levodopa regimen; however, all of the available treatments provide a good possibility of benefit to the patient. Deep brain stimulation surgery is an option for patients with medically intractable severe motor fluctuations.

Parkinsonism is a common, age-related syndrome, characterized by resting tremor, bradykinesias, rigidity, and postural reflex impairment. Though Parkinsonism is not very difficult to recognize, all Parkinsonism is not created equal and it is important to distinguish among the most common identifiable syndromes. This review discusses the key clinical features of these various syndromes, including Parkinson's disease, progressive supranuclear palsy, multiple system atrophy, corticobasal ganglionic degeneration, Lewy body disease, vascular Parkinsonism, and Parkinsonism with no clear etiology. Symptomatology and diagnostic testing for each syndrome are discussed and 4 typical cases are analyzed to offer clinicians guidance in making a differential diagnosis for Parkinsonism.