Primary Myoclonus-Dystonia: A Diagnosis Often Missed in Children.

Primary myoclonus-dystonia is a childhood-onset autosomal-dominant movement disorder with myoclonic jerks and dystonia. The authors report 9 children (4 boys, 5 girls) with myoclonus-dystonia from 8 families seen over a 4-year period at Cleveland Clinic. The mean age of onset of symptoms was 2.8 years, but the diagnosis was made at a mean of 7.3 years. Myoclonus was the presenting symptom in 8 children. A known pathogenic mutation in the ε-sarcoglycan gene (SGCE) was identified in 4 of the 9 children, and 2 other children had novel mutations in the same gene. Good response to trihexyphenidyl and clonazepam was seen. Two patients underwent deep brain stimulation surgery of the bilateral globus pallidus pars interna. In 7 children, the diagnosis of myoclonus-dystonia was not considered by the referring child neurologists, which led to extensive investigations and a delay in the final diagnosis. In this report, the authors highlight the need for increased awareness of this entity among child neurologists.