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Early Diagnosis of Parkinson's Disease: Recommendations From Diagnostic Clinical Guidelines
Rajesh Pahwa, MD; and Kelly E. Lyons, PhD
Parkinson's Disease: Health-Related Quality of Life, Economic Cost, and Implications of Early Treatment
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Early Diagnosis of Parkinson's Disease: Recommendations From Diagnostic Clinical Guidelines

Rajesh Pahwa, MD; and Kelly E. Lyons, PhD
In summary, the specific utility of acute levodopa and apomorphine challenge, according to the AAN guidelines, is for confirming an uncertain PD diagnosis, although the guidelines also note a lack of data regarding any advantage over clinical diagnostic criteria.19 The NCCCC and SIGN guidelines advise against using acute levodopa and apomorphine challenge for differential diagnosis, noting that these methods do not add any more diagnostic information than chronic use of levodopa.20,21 Both of these guidelines also point out the adverse events associated with acute levodopa challenge (eg, neuropsychiatric effects, postural hypotension) and apomorphine challenge (drowsiness, nausea, vomiting, hypotension, sweating), and the risk to patients, particularly older patients or those with cognitive dysfunction.20,21

Smell Testing

The frequency of olfactory impairment in PD provides an opportunity for differential diagnosis, although this particular dysfunction occurs to some extent in many parkinsonian patients. The AAN guidelines support consideration of olfactory testing for differentiation between PD and PSP, as well as PD and corticobasal degeneration, but not for differentiation of PD and MSA. Olfactory testing was associated with a diagnostic sensitivity of 77% and a specificity of 85%.19,29 The 2 UK guidelines recommend against olfactory testing in the clinical setting.20,21


Single Photon Emission Computed Tomography

Single photon emission computed tomography (SPECT) imaging uses a radiolabeled compound as a probe of dopamine transporters to study the progression of presynaptic dopaminergic degeneration. The AAN guidelines indicated that SPECT may be useful in differentiating PD from essential tremor but indicated that there was insufficient evidence to determine if SPECT is useful to differentiate various forms of parkinsonism.19 The NCCCC guidelines expressed ambivalence regarding the use of SPECT, but cited studies that support its use in differentiating essential tremor from dopaminergic deficiency in patients with upper limb postural or action tremor.21 The NCCCC further stated that SPECT may eventually be useful in distinguishing drug-induced and psychogenic parkinsonism from a state of dopaminergic deficiency. The SIGN guidelines support the use of SPECT to distinguish PD from nonneurodegenerative parkinsonism and tremor disorders, but not from neurodegenerative forms of parkinsonism.20

Magnetic Resonance Imaging

The AAN guidelines found magnetic resonance imaging (MRI) to possibly be useful in differentiating PD and MSA.19 The NCCCC guidelines regard structural MRI as potentially useful for differential diagnosis of PD from other forms of parkinsonism if conducted by an expert practitioner, but recommends against its diagnostic use otherwise.21 The SIGN guidelines recognize MRI as a useful tool for evaluating cerebrovascular disease to differentiate idiopathic PD from vascular parkinsonism. MRI is effective for measuring the extent of brain atrophy and to determine the presence of structural lesions that can be associated with parkinsonism, but SIGN advocates against the use of MRI for diagnosis of idiopathic PD.20


Transcranial sonography is not supported in the SIGN guidelines for differential diagnosis, whereas the AAN and NCCCC find insufficient data to make a recommendation.19-21

Positron Emission Tomography

None of the guidelines supports the use of positron emission tomography for differential diagnosis in PD.19-21


An early and accurate diagnosis of PD is critical to developing the most appropriate treatment strategy to maintain the best QOL for as long as possible. Unfortunately, the early recognition of PD can be challenging as there are other movement disorders, such as MSA, PSP, drug-induced parkinsonism, vascular parkinsonism, and essential tremor, which can initially appear very similar to PD. Several guidelines have been published to assist in the accurate diagnosis of PD. Studies have shown that these guidelines are often underutilized; however, when used, they do appear to improve diagnostic accuracy. As there are no definitive clinical tests to confirm PD at this time, the most accurate PD diagnosis has been shown to come from a neurologist specializing in movement disorders. Although the published guidelines are not in complete agreement, when used by a physician experienced in the diagnosis and treatment of PD, levodopa or apomorphine challenges, olfactory testing, and various neuroimaging techniques may have some utility in the diagnosis of PD. Improved awareness of the clinical features of PD and differential diagnosis, as well as knowledge of and appropriate application of diagnostic aids, will allow clinicians to more accurately diagnose and treat early PD.

Author Affiliation: Parkinson's Disease and Movement Disorder Center, University of Kansas Medical Center, Kansas City.

Funding Source: Financial support for this work was provided by Teva Neurosciences, Inc.

Author Disclosure: Drs Pahwa and Lyons report that they are consultants/ members of the advisory boards and have received honoraria from Teva.

Authorship Information: Concept and design (RP, KEL); acquisition of data/information (RP, KEL); analysis and interpretation of data/information (RP, KEL); and critical revision of the manuscript for important intellectual content (RP, KEL).

Address correspondence to: Kelly E. Lyons, PhD, University of Kansas Medical Center, 3599 Rainbow Blvd, Kansas City, KS 66160. E-mail:


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