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Early Diagnosis of Parkinson's Disease: Recommendations From Diagnostic Clinical Guidelines
Rajesh Pahwa, MD; and Kelly E. Lyons, PhD
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Early Diagnosis of Parkinson's Disease: Recommendations From Diagnostic Clinical Guidelines

Rajesh Pahwa, MD; and Kelly E. Lyons, PhD

Abstract

Therapeutic options for Parkinson's disease (PD) are currently limited to symptomatic agents. Levodopa is the most efficacious treatment; however, higher doses and long-term use are associated with adverse effects such as motor fluctuations and dyskinesia. Early treatment of PD with other agents such as dopamine agonists and monoamine oxidase type B inhibitors can provide symptomatic benefit and delay initiation of levodopa therapy. Early treatment of PD is contingent upon early and accurate diagnosis of the disease, which can be challenging because there are no biomarkers or neuroimaging or other clinical tests available to confirm the diagnosis. PD diagnosis is currently based on the presence or absence of various clinical features and the experience of the treating physician. A definitive diagnosis can be made only after autopsy. Moreover, the signs and symptoms present in early PD can resemble those of a number of other movement disorders, particularly other forms of parkinsonism, such as multiple system atrophy, drug-induced parkinsonism, and vascular parkinsonism, as well as diffuse Lewy body disease and essential tremor. Nevertheless, diagnosis of PD based on clinical features and response to antiparkinsonian medication can be achieved with a fairly high level of accuracy, particularly when made by a physician specializing in movement disorders. This article reviews and summarizes published recommendations for the clinical diagnosis of PD.

(Am J Manag Care. 2010;16:S94-S99)

 

Introduction

Parkinson's disease (PD) is a disabling neurodegenerative disorder with a prevalence rate estimated as high as 329 per 100,000 persons in the United States.1 The annual incidence rate has been estimated to range from 16 to 19 per 100,000 persons when the diagnosis is made by a movement disorder specialist.2 PD primarily affects people over the age of 50 years, and prevalence and incidence rates increase with age. Therefore, aging of the general population is likely to result in a dramatic increase in the number of people diagnosed with PD. One study projected that by the year 2030, the number of people over the age of 50 (and consequently the number of persons with PD) will double, resulting in an estimated 9 million persons with PD worldwide.3





Although there is currently no cure for PD, and the therapeutic armamentarium is limited to symptomatic agents, appropriate and timely treatment has been shown to have a beneficial effect on the course of the disease.4-6 The most efficacious therapeutic agent for PD is levodopa, which is converted to dopamine through decarboxylation.7 Although levodopa is the gold standard in the treatment of PD, its use is often delayed to avoid the early development of motor fluctuations and dyskinesia. In early, mild PD, therapy is often initiated with a monoamine oxidase type B (MAO-B) inhibitor or a dopamine agonist, reserving the use of levodopa until functional impairment is more significant.7,8





Multiple studies have demonstrated that dopamine agonists have a mild-to-moderate benefit on PD motor symptoms.7,8 In addition, several studies have demonstrated that the early use of dopamine agonists can delay the need for levodopa and, consequently, the development of motor fluctuations and dyskinesia.4,7 However, dopamine agonists can be associated with bothersome adverse events, including hallucinations, pedal edema, impulse control disorders, and daytime sleepiness. Data also support the early use of MAO-B inhibitors for early PD motor symptoms. Although MAO-B inhibitors are usually less effective than levodopa or dopamine agonists, they are associated with significantly fewer adverse events.4,6,9,10 Early treatment of PD improves motor symptoms, but may also ameliorate nonmotor symptoms, such as depression, and can enhance patients' quality of life (QOL).11 Moreover, third-party payer data suggest that early treatment of PD is a cost-effective strategy.12





The effects of early treatment can be significant but are contingent upon timely and accurate identification of the disease. Several guidelines are available to help clinicians recognize the signs and symptoms of PD and to provide insight and recommendations for differential diagnosis. Despite the availability of clinical guidelines, underdiagnosis and misdiagnosis of PD is quite common. Among general neurologists, Hughes et al found that nearly 24% of PD diagnoses were incorrect (when confirmed by autopsy), with the most common misdiagnoses including progressive supranuclear palsy (PSP), multiple system atrophy (MSA), and Alzheimer's disease.13





A population-based study using the United Kingdom Parkinson's Disease Society Brain Bank criteria found that at least 15% of patients diagnosed with PD were misdiagnosed, whereas 19% of those who did have PD were inaccurately diagnosed with a different disorder.14 In contrast, Jankovic et al examined data in 800 patients with PD enrolled in a clinical trial for early treatment. These patients were reexamined 6 years after the initial diagnosis by a neurologist specializing in movement disorders, and only 8% of the initial diagnoses were incorrect. In other words, initial diagnoses by a movement disorder specialist were accurate in 92% of cases.15





Although there are several clinical practice guidelines for the diagnosis and treatment of PD, studies indicate that they are underutilized by healthcare professionals treating PD. A German study found that only 53% of 181 private practice neurologists were aware of clinical practice guidelines for the diagnosis of PD.16 In addition, it was demonstrated that those who were aware of the guidelines for PD had significantly greater knowledge regarding the differential diagnosis and treatment of PD. Another German study reported that 88% of 213 private practice neurologists were aware of PD-specific guidelines; more than 90% of those who were aware of the guidelines reported that they were beneficial and used them in clinical practice.17 In the United States, practice patterns by physicians and nonphysician providers such as nurse practitioners and physician assistants in the treatment of PD were in agreement with recommended clinical guidelines only about half of the time.18 Moreover, physicians were 3 times less likely than nonphysician providers to refer patients to a specialist for confirmation of a PD diagnosis.18





In the United States, the primary guidelines for diagnosing PD are those published by the American Academy of Neurology (AAN).19 This article reviews recommendations from the AAN, as well as 2 other comprehensive guidelines for PD that originate from the United Kingdom: (1) the clinical guidelines published by the Royal College of Physicians and produced by the National Collaborating Centre for Chronic Conditions (NCCCC), which is funded by the National Institute for Health and Clinical Excellence, and (2) the clinical guidelines produced by the Scottish Intercollegiate Guidelines Network (SIGN).20,21 Also discussed are the most widely used diagnostic criteria for PD-those defined by the United Kingdom Parkinson's Disease Society Brain Bank.13,19







Definitions and Diagnostic Criteria

The criteria for diagnosis of PD set forth by the United Kingdom Parkinson's Disease Society Brain Bank consists of 3 diagnostic steps (Table):





1. Determining whether a patient's symptoms fall within the broader category of parkinsonism (defined as presentation of bradykinesia in addition to muscular rigidity, 4- to 6-Hz rest tremor, or postural instability unrelated to visual, vestibular, cerebellar, or proprioceptive dysfunction);

2. Ruling out those patients presenting with a spectrum of exclusion criteria; and

3. Including those patients presenting with specific positive criteria, any 3 of which, taken together, constitute a PD diagnosis after both stages 1 and 2 have been met.13





In the study by Hughes et al, in which only 76% of PD diagnoses were correct, the full extent to which the United Kingdom Parkinson's Disease Society Brain Bank criteria were being used by neurologists was unclear. Nevertheless, when the study authors applied the United Kingdom Parkinson's Disease Society Brain Bank criteria to 100% of these cases, albeit retrospectively, they observed that diagnostic accuracy increased to 82%. Confirmation of diagnoses was based on the pathologic finding of Lewy bodies.13 In a subsequent study, when United Kingdom Parkinson's Disease Society Brain Bank criteria were applied to 100 cases, there was 90% diagnostic accuracy as confirmed by autopsy.22 This degree of accuracy was as high as could be expected using diagnostic methods based entirely on clinical features.





The NCCCC guidelines are largely in agreement with the United Kingdom Parkinson's Disease Society Brain Bank criteria, noting that hypokinesia in addition to bradykinesia is a common PD sign, along with rest tremor and rigidity.21 The NCCCC guidelines note that initial symptoms will typically be unilateral, and symptoms will likely become bilateral over time. The authors added, however, that there is no single means of identifying PD, and that an absolutely definitive diagnosis can, at present, only be achieved postmortem with detection of Lewy bodies in brain tissue and catecholaminergic neuron degeneration.21





The Parkinson Study Group observed several features of patients misdiagnosed with PD that tend to separate them from patients with early PD. Compared with patients with early PD, misdiagnosed patients presented with the following: (1) higher Hoehn and Yahr stage, (2) higher Unified Parkinson's Disease Rating Scale (UPDRS) scores for bradykinesia, (3) postural instability and gait difficulty as initial symptoms, and (4) lower tremor scores.15 Based on this study and several others, the AAN guidelines recommended that initial or early falling, poor response to levodopa, symmetry at onset, rapid progression, lack of tremor, and dysautonomia should be used to distinguish PD from other forms of parkinsonism early in the disease course.19





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