Myoclonus dystonia without dystonia

Myoclonus dystonia is one of several dystonia plus syndromes and the most common nonepileptic type of myoclonus disease. It usually starts in infancy or adolescence, and it is subject to autosomal dominant inheritance with maternal imprinting. We report the case of two boys with myoclonus dystonia.

One boy was investigated from the age of 2.5 to 5.5 years. Marked myoclonias triggered by fine motor factors impaired his activities of daily living. A dystonic component was noted at the age of 2.5 years, but it was not observed after the age of 3 years. The patient's myoclonia could be markedly reduced but not entirely resolved by treatment with Trihexyphenidyl 1 mg/kg/d, but the dosage is currently being increased. In terms of molecular genetics a deletion in the SGCE gene on chromosome 7q21 was found.

The second case is that of an 8-year-old boy with myoclonia during bimanual activities. A dystonic component was not present. As the symptoms caused much less subjective impairment, no drug treatment was attempted. A previously unreported pathogenic mutation in the SGCE gene was found.

Myoclonus dystonia may occur without dystonia (in as many as 20% of cases). The diagnosis is rendered difficult by the fact that most textbooks report a connection between forms of dystonia and myoclonus dystonia, but not for myoclonia. The dystonic component may be aggravated over time in the individual patient, but may also be reduced.

Myoclonus dystonia has been observed to cause a memory engram, which permits targeted genetic investigation in respect of DYT 11 without laborious additional investigations. Therapeutic options are available to make daily life easier for children, especially in executing fine motor skills. This has a positive impact on the child's overall development. Appropriate diagnosis and therapy is of prime importance, also because of the imminent risk of alcohol abuse in nontreated patients (reduction of myoclonia by consumption of alcohol).