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Parkinson Disease in Young Adults: Differential Diagnoses & Workup

Author: Stephen T Gancher, MD, Adjunct Associate Professor, Department of Neurology, Oregon Health Sciences University
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Updated: Aug 11, 2008

Differential Diagnoses

Other Problems to Be Considered

Several features should suggest the possibility of a form of secondary parkinsonism. The first clue is that the response to levodopa or other medications is generally poor or absent in diseases that cause parkinsonism other than idiopathic Parkinson disease. Second, this group of diseases generally progresses differently than idiopathic Parkinson disease. Marked waxing and waning of symptoms, rapid progression, or a stepwise course are atypical in Parkinson disease and should suggest an alternative diagnosis. Finally, the occurrence of certain neurological signs and symptoms that are not seen in idiopathic Parkinson disease should also serve as a clue to consider other diseases. These include prominent and severe dysautonomia, ophthalmoplegia, dysarthria, ataxia, neuropathy, pyramidal tract signs, early dementia, and aphasia or apraxia.

Two other causes of parkinsonism should be carefully considered as well.

Drug-induced parkinsonism: Parkinsonism induced by drugs (eg, antiemetics, major tranquilizers) is a common condition and is probably more prevalent overall than Parkinson disease, especially in younger patients. This may cause neurological signs and symptoms very similar to idiopathic Parkinson disease. Patients with parkinsonian features should have their medications reviewed in detail. Even low doses of antiemetics or antipsychotic medications can cause parkinsonism.

Multi-infarct state: Patients with a multi-infarct state usually have a stepwise downhill course, have signs of pyramidal tract dysfunction, do not have dysautonomia or neuropathy, and do not respond to levodopa. However, some patients with parkinsonism with prominent freezing and gait disorder ("lower half parkinsonism") may not have these atypical historical features, yet may have parkinsonism on a vascular basis.

Workup

Laboratory Studies

• Generally, no specific lab tests are needed in the evaluation of patients with Parkinson disease. In adolescents and young adults, Parkinson disease is extremely rare; therefore, other causes of parkinsonism need to be carefully excluded, particularly any exposure to antipsychotic or antiemetic medications. In very young patients or in patients with a family history of Parkinson disease, a genetic test for the parkin mutation may be considered and may be helpful to confirm the diagnosis.
• Wilson disease should be considered carefully and workup should include screening of plasma ceruloplasmin; if low, measurement of 24-hour urinary copper excretion and slit-lamp examination for Kayser-Fleischer rings must be done.
• Huntington disease can produce rigidity and bradykinesia in young adults or adolescents and may require DNA analysis for exclusion.
• Neuroacanthocytosis can cause dystonia and rigidity in addition to other neurological features. The workup of this condition is discussed in more detail in Neuroacanthocytosis.
• Dopa-responsive dystonia should be considered in patients with juvenile-onset dystonia and parkinsonism, particularly with diurnal fluctuations in symptoms. A number of tests are available.
  • The simplest test is a diagnostic trial of levodopa, as the response to low doses of levodopa is nearly complete.
  • Biochemical tests include measurement of cerebrospinal fluid concentrations of biopterin, neopterin, and the neurotransmitter metabolites homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3 methoxy-4-hydroxyphenylglycol (MHPG). In both forms of dopa-responsive dystonia, an altered pattern of decreases in these compounds is observed.
  • Another biochemical test that is helpful in GTPCH-1 deficiency is to administer an oral dose of phenylalanine and then measure plasma amino acids at intervals. In this condition, patients are less able to convert phenylalanine to tyrosine. The sensitivity and specificity of this test, though, is unknown.
  • A final method to test for this condition is by molecular genetic analysis; genetic tests are available for both GTPCH-1 deficiency and TH deficiency.

Imaging Studies

• Brain imaging is generally unnecessary in patients with typical Parkinson disease, especially if the patient has an asymmetric presentation, tremor, and a good response to medications.
• Brain imaging (CT scan or MRI) must be obtained in patients younger than 50 years with atypical physical findings or an atypical history. Rare causes of parkinsonism that may be recognized on CT scan or MRI include basal ganglia calcification or iron deposition, hydrocephalus, multiple infarcts, multiple sclerosis, brain tumors, leukodystrophies, or striatal necrosis due to mitochondrial disease.
• Single-photon emission CT (SPECT) and positron emission tomography (PET) are functional imaging studies that may show basal ganglia abnormalities in very mildly affected patients. These are not commercially available, however, and do not reliably differentiate Parkinson disease from other forms of parkinsonism.

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