[Hereditary essential myoclonus. Report of a family].

The occurrence of myoclonic and dystonic movements as an isolated expression of a neurologic condition of hereditary pattern have been scarcely described in literature. For this entity some authors proposed the denomination "hereditary myoclonic dystonia" while others prefer the use of the expression "hereditary essential myoclonus". We present a family in which this unusual association of abnormal movements affected several members in three generations. The propositus patient is a 14-year-old girl who have noticed the dystonic movements by 7 years of age and the myoclonic ones by 13 years of age, with a slow progression. There was no reference about the effect of alcohol (abstemious patient). There was a family history of similar cases. The supplementary investigation (seric dosage of cupper, ceruloplasmine, T3, T4, TSH; acanthocytes search; CSF examination; CT scan and MRI of the head) did not show any abnormality. Clonazepam was the only medication that lead to a clinical improvement, reducing both movements.