From the VA Medical Center (Dr. Lehosit) and the Parkinson’s and Movement Disorders Center, Virginia Commonwealth University (Dr. Cloud), Richmond, VA.
Abstract
Objective: To provide an overview of the importance and challenges of accurate diagnosis of early idiopathic Parkinson’s disease and practical guidelines for clinicians.
Methods: Review of the relevant literature.
Results: Idiopathic Parkinson’s disease is a common neurodegenerative disorder causing a wide spectrum of motor and nonmotor symptoms. The cardinal motor features include resting tremors, bradykinesia, rigidity, and postural instability. The diagnosis is clinical, and ancillary laboratory or radiology tests are unnecessary in typical cases. Despite the use of validated diagnostic criteria, misdiagnosis is common, especially early in the disease process. This is largely due to the phenotypic heterogeneity in the idiopathic Parkinson’s disease population as well phenotypic overlapping with other diseases. The diseases most commonly confused with idiopathic Parkinson’s disease are the Parkinson-plus syndromes (dementia with Lewy bodies, multiple system atrophy, progressive supranuclear palsy, and corticobasal degeneration), vascular parkinsonism, drug-induced parkinsonism, dopa responsive dystonia, normal pressure hydrocephalus, and essential tremor. Since the diagnosis of these other diseases is also clinical, familiarity with their typical presentations and most current diagnostic criteria is helpful. Brain MRI can be helpful in diagnosing some of the diseases, though brain imaging is most commonly unremarkable in idiopathic Parkinson’s disease. DaTscan has an FDA indication to assist in the evaluation of adults with parkinsonian syndromes. It should not be used in typical cases but can be a useful adjunct to other diagnostic evaluations in atypical cases.
Conclusion: Despite the challenges involved, accurate and early diagnosis of idiopathic Parkinson’s disease is essential for optimal patient education, counseling, and treatment.
Idiopathic Parkinson’s disease (IPD) is a common neurodenerative disease, affecting 1% of the population over the age of 65 [1]. A definitive diagnosis requires the postmortem findings of degeneration of the substantia nigra pars compacta and the presence of Lewy bodies (insoluble cytoplasmic inclusions composed of aggregated alpha-synuclein). In the later stages of the disease, a correct clinical diagnosis is made in more than 90% of patients [2]. Early on, however, clinical diagnosis is less reliable. For clinicians, distinguishing early IPD from other parkinsonian syndromes can be extraordinarily challenging because these conditions, especially in the earliest stages, present with highly variable yet overlapping phenotypes [3]. Furthermore, most of the diseases in the differential diagnosis, including IPD itself, are clinical diagnoses made on the basis of history and examination without the benefit of laboratory or radiology data. A high level of clinical acumen is therefore required for early and accurate diagnosis. Recent clinical trials in which subspecialists performed stringent diagnostic assessments to identify subjects with clinically diagnosed IPD later found that some subjects had normal functional dopamine imaging, suggesting that they probably did not have IPD [4,5]. These trials served to highlight the possibility of misdiagnosis, even in the hands of highly trained subspecialists. Early and accurate diagnosis is of paramount importance for many reasons. First, treatment approaches differ significantly across many of these diseases. Second, as neuroprotective interventions that are currently under investigation become available, long-term outcomes may significantly improve with earlier diagnosis and intervention. Third, some of these diseases are prognostically very different from one another, so accurate diagnosis enables better counseling and setting realistic expectations for progression.
