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The Parkinson's-Reversing Breakthrough

What is Parkinsons Disease

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Differential Diagnosis

John Morgan and Kapil D. Sethi

Department of Neurology, Medical College of Georgia, Augusta, Georgia, U.S.A.

Parkinsonism refers to a clinical syndrome characterized by a variable combination of rest tremor, bradykinesia or akinesia, cogwheel rigidity, and postural instability. In general, two of these four features must be present to make a diagnosis of parkinsonism. However, the situation is complicated by rare cases of pure akinesia in the absence of tremor and rigidity that have the classic pathology of Parkinson's disease (PD) (1). Within the rubric of parkinsonism there are a myriad of disorders, some yet unclassified (Table 1).

The most common cause of parkinsonism is PD. Pathologically, PD is characterized by cell loss in the substantia nigra and other pigmented nuclei of the brain-stem. Characteristic inclusions called Lewy bodies are found in the remaining neurons and the term "Lewy body parkinsonism" is sometimes used synonymously with PD. Some researchers consider it most appropriate to refer to even the clinical picture of PD as "Parkinson's syndrome" on the premise that PD may not be one disease. Whereas the purists demand the presence of Lewy bodies at autopsy to diagnose PD, these inclusions may not be present in some inherited forms of otherwise classic PD. Currently, one such condition, parkin, has been mapped to chromosome 6 (2). This autosomal recessive parkinsonism of young onset differs pathologically from sporadic disease as Lewy bodies are usually absent. The clinical picture can be similar to idio-pathic PD including the presence of tremor (3). There are other forms of inherited parkinsonism including LRRK2 mutation, where typical Lewy body pathology is found (4,5).

In the absence of a known biological marker, the challenge facing the clinician is to make an accurate diagnosis of PD and differentiate it from other similar conditions. This review will give a practical approach to the differential diagnosis of parkinsonism and examine the diagnostic accuracy of a clinical diagnosis of PD.

IDIOPATHIC PARKINSON'S DISEASE

The onset of PD is gradual and the course slowly progressive albeit at different rates in different individuals. In most series, 65% to 70% of the patients present with an asymmetric tremor especially of the upper extremity (6). After a variable delay, the disorder progresses to the other side with bilateral bradykinesia and gait difficulty that takes the form of festination and, in advanced cases, freezing. Postural instability and falls tend to be a late feature. Eye movements may show saccadic pursuit and upgaze may be limited in the elderly. Downgaze is normal. Autonomic disturbances may occur but are not severe in early disease. Depression may occur early in the disease but dementia, as a presenting manifestation, is not a feature of PD. Several signs should ring alarm bells when considering a diagnosis of PD. These include early dementia, early autonomic dysfunction, gaze difficulty (especially looking down), signs of upper motor neuron lesion or cerebellar signs in addition to parkinsonism, stepwise deterioration, and apraxia (Table 2).

TABLE 1 Classification of Parkinsonism

Primary Parkinson's disease Sporadic Familial Secondary parkinsonism Drug-induced parkinsonism (DIP) Toxin-induced parkinsonism Infectious

Creutzfeld-Jakob disease (CJD) Metabolic Structural Tumor

Subdural hematoma Vascular

Other Degenerative Disorders Corticobasal degeneration (CBD) Dementia with Lewy bodies (DLB) Multiple-system atrophy (MSA) Progressive supranuclear palsy (PSP) Spinocerebellar ataxias (SCA) Hallervorden-Spatz disease Huntington's disease (HD) Neuroacanthocytosis Wilson's disease

X-linked dystonia-parkinsonism (Lubag)

Conditions Mimicking Parkinsonism

Essential tremor (ET) is more common than PD and results in tremor that affects primarily the upper extremities, head, and voice (7). The tremor is absent at rest, except in most severe cases, and is increased by maintained posture and voluntary movement. Mild cogwheeling may be present but bradykinesia is not a feature (Table 3). The confusion occurs when a patient with a long history of ET begins to develop signs of parkinsonism. Patients with PD may have a prominent action tremor adding to the diagnostic uncertainty. In addition, there are elderly patients with ET who exhibit mild bradykinesia on detailed testing (8). It is debatable if patients with ET

TABLE 2 Features Indicating an Alternate Diagnosis to Parkinson's Disease

Early or predominant feature Disease

TABLE 2 Features Indicating an Alternate Diagnosis to Parkinson's Disease

Early or predominant feature Disease

Young onset

Drug or toxin-induced parkinsonism, Wilson's disease,

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