Does a normal imaging scan rule out Parkinson's disease (PD)?

From the Guidelines

A normal imaging scan does not rule out Parkinson's disease (PD). Parkinson's disease is primarily diagnosed through clinical evaluation of symptoms by a neurologist, including tremor, rigidity, bradykinesia (slowness of movement), and postural instability. Standard imaging tests like CT scans or routine MRIs often appear normal in early Parkinson's disease because the structural changes are microscopic and involve the loss of dopamine-producing neurons in the substantia nigra region of the brain.

Key Points to Consider

• More specialized imaging techniques such as I-123 ioflupane SPECT/CT can help support a diagnosis by showing reduced dopamine activity in the brain, as it binds to the dopamine transporters and can be used to demonstrate the loss of presynaptic dopaminergic neurons in PD 1.
• A normal I-123 ioflupane SPECT/CT essentially excludes Parkinsonian syndromes, but this does not necessarily mean that a normal scan rules out PD, as the disease can be in very early stages or the scan may not detect all cases 1.
• The role of new nuclear medicine tracers, designed to target the postsynaptic dopamine receptors (D1 and D2), including 11C-raclopride-PET and I-123-iodobenzamide SPECT scans, may grow in the future, but they are yet to be approved by the US FDA for clinical use 1.

Clinical Implications

• The gold standard for diagnosis remains the clinical assessment of symptoms and their progression over time, along with response to medications like levodopa.
• Patients with suspected Parkinson's should see a movement disorder specialist even if their conventional brain scans appear normal, as clinical evaluation is crucial for diagnosis and management.

From the Research

Normal Imaging Scan and Parkinson's Disease

• A normal imaging scan does not necessarily rule out Parkinson's disease (PD) 2.
• Studies have shown that some patients with old-onset PD may have normal dopamine transporter single-photon emission computed tomography (DAT-SPECT) results despite having dopaminergic degeneration 2.
• The probability of a normal scan outcome in clinical brain DAT imaging increases with factors such as a long duration of uncertain motor symptoms and suspicion of medication-induced parkinsonism 3.

Diagnostic Uncertainty and Imaging

• In cases of diagnostic uncertainty, evaluation of nigrostriatal dopaminergic degeneration (NSDD) by imaging of the dopamine transporter using DaTscan with single-photon emission computed tomography (SPECT) brain imaging may be helpful 4.
• DaTscan imaging can be useful in several clinical scenarios to determine if NSDD is present, including in patients with early subtle symptoms, suboptimal response to levodopa, and prominent action tremor 4.
• DAT-SPECT scanning can be used when there is diagnostic difficulty differentiating from non-neurodegenerative Parkinsonism 5.

Scan Results and Diagnosis

• Abnormal scan results were found in 56.3% of patients in one study, with independent factors associated with abnormal scans including older age, asymmetry of motor symptoms, and shorter symptom duration 3.
• In another study, 40% of patients had an abnormal scan result, while 53% had a normal scan result, and 7% had an equivocal scan 5.
• Pre-scan diagnoses were generally consistent with scan results, but the diagnosis was changed in 37% of patients and clinical management was changed in 42% of patients after DaT scanning 5.