Dystonia is frequent in early-onset parkinsonism (EOP) and sometimes its presenting sign. 1, 2 Conversely, parkinsonian signs occur in dopa-responsive dystonia (DRD), especially in later stages, and may even be the only finding in relatives of patients with clinically typical DRD. 3 Both conditions may have a similar age at onset and respond well to treatment with levodopa, and patients may report sleep benefit and diurnal variation of symptoms in both conditions. Due to this phenotypic overlap, categorization of the early-onset dystonia–parkinsonism syndromes may pose a diagnostic challenge.

Dominantly, inherited mutations in the GTP cyclohydrolase I (GCHI) gene can be found in over 80% of the clinical typical cases of DRD but only when conventional screening methods and expensive gene dosage analyses are combined. 4 The most common known cause of EOP is recessively transmitted mutations in the parkin gene, the detection of which also requires comprehensive screening for small mutations and exon rearrangements. Given these technical considerations and, more importantly, because of the different prognosis of the two conditions, a fast, inexpensive marker or tool would be helpful in establishing a diagnosis of neurodegenerative EOP vs nondegenerative DRD. To date, diagnostic approaches to distinguish between the two diseases with neuroimaging (CT and MRI) have not been successful. The more recent method of transcranial sonography (TCS) of the brain parenchyma may prove a promising alternative as an easily applicable and low-cost neuroimaging technique. The substantia nigra (SN) shows a distinct hyperechogenic pattern on TCS in about 90% of patients with Parkinson disease (PD) 5 that is associated with a significant reduction of 18F-dopa uptake in the striatum and has been related to increased tissue concentrations of iron and loss of neuromelanin. Recently, SN hyperechogenicity has been described in symptomatic and asymptomatic carriers of parkin mutations. 6 There are no published data on TCS of the midbrain in patients with DRD. To determine whether TCS can detect differences in SN echogenicity in patients with DRD vs parkin-associated EOP, we studied 5 patients with genetically proven DRD (5 women, mean age 46.0 12.2 years, mean disease duration 31.0 13.8 years), 5 patients with EOP and homozygous or compound heterozygous parkin mutations (4 men, 1 woman, mean age 59.0 15.4 years, mean disease duration 12.3 6.3 years, mean Unified Parkin-