How to diagnose Dopa-responsive dystonia ?
How is dopa-responsive dystonia diagnosed? Dopa-responsive dystonia (DRD) is diagnosed based on the signs and symptoms present, results of laboratory tests (sometimes including genetic testing), and response to therapy with levodopa. If DRD is suspected, a therapeutic trial with low doses of levodopa remains the most practical approach to the diagnosis. It is generally agreed that people with childhood-onset dystonia of unknown cause should be treated initially with levodopa. The characteristic symptoms and response to treatment are sufficient to establish the diagnosis for people with the most common form, autosomal dominant DRD. There is only one gene in which mutations are known to cause this form of DRD, but not all people with the disorder are found to have a mutation in the responsible gene. While finding a mutation may provide information about prognosis, it does not alter the treatment. Other types of laboratory tests, such as measuring specific substances or enzymes in the blood or cerebrospinal fluid (CSF), may be useful to support the diagnosis. For tyrosine hydroxylase deficiency, an autosomal recessive genetic cause of DRD, molecular genetic testing has confirmed the presence of mutations in all affected people to date. Specific laboratory tests performed on CSF help support the diagnosis but are not diagnostic on their own. For sepiapterin reductase deficiency, a very rare autosomal recessive form of DRD, there are distinctive findings in CSF and reduced or absent activity of sepiapterin reductase in fibroblasts. Molecular genetic testing can identify mutations in the responsible gene and confirm the diagnosis of this form of DRD. The major conditions that may have a similar presentation to DRD and are part of the differential diagnosis include early-onset parkinsonism, early-onset primary dystonia, and cerebral palsy or spastic paraplegia. People with specific questions about being evaluated for any form of dystonia should speak with a neurologist or other health care provider.