Investigations

1st investigations to order

levodopa responsiveness

Test
Result
Test

Dopa-responsive dystonia should be ruled out in early-onset dystonia cases (<40 years).[37]​​

Levodopa is given for at least 4 weeks to assess response.[38]

Result

positive if clinical improvement following administration

Investigations to consider

cranial magnetic resonance imaging

Test
Result
Test

Should be performed if an acquired cause of dystonia is suspected.[39]​ Consider if hemidystonia (multiple ipsilateral body parts, e.g., arm and leg) or other neurological signs are present in addition to dystonia. Can also consider if presentation is acute and there has been no exposure to antidopaminergic drugs. No evidence to support the yield of imaging in primary focal, segmental, or generalised dystonias.

Result

normal

serum ceruloplasmin

Test
Result
Test

Consider if Wilson's disease is suspected.[37]

Serum ceruloplasmin <20 mg/dL suggests dystonia due to Wilson's disease.

Result

normal

24-hour urine copper

Test
Result
Test

Consider if Wilson's disease is suspected. Levels >100 micrograms suggest Wilson's disease.

False positives may occur in patients with cholestasis, autoimmune conditions, or protein-losing enteropathy.

Result

normal

TOR1A (also known as DYT1) gene testing

Test
Result
Test

Consider testing in patients with any form of isolated dystonia younger than 26 years old or any patient with a relative with dystonia with onset before the age of 26 years.[39]

Result

variable; presence of GAG deletion in at least one allele of the TOR1A gene

GCH1 gene testing

Test
Result
Test

Can be considered in some cases to confirm the presence of some causes of dopa-responsive dystonia.[16]​​[17]

Result

variable; GCH1 gene mutations usually result in a single amino acid change in the GTP cyclohydrolase 1 enzyme

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