Orthostatic paroxysmal dystonia

Paroxysmal movement disorders

Paroxysmal dyskinesias represent a group of episodic abnormal involuntary movements manifested by recurrent attacks of dystonia, chorea, athetosis, or a combination of these disorders. Paroxysmal kinesigenic dyskinesia, paroxysmal nonkinesigenic dyskinesia, paroxysmal exertion-induced dyskinesia, and paroxysmal hypnogenic dyskinesia are distinguished clinically by precipitating factors, duration and frequency of attacks, and response to medication. Primary paroxysmal dyskinesias are usually autosomal dominant genetic conditions. Secondary paroxysmal dyskinesias can be the symptoms of different neurologic and medical disorders. This review summarizes the updates on etiology, pathophysiology, genetics, clinical presentation, differential diagnosis, and treatment of paroxysmal dyskinesias and other episodic movement disorders.

Paroxysmal dyskinesias

Paroxysmal movement disorders are a relatively rare and heterogenous group of conditions manifesting as episodic dyskinesia lasting a brief duration. Three forms are clearly recognized, namely, paroxysmal kinesigenic (PKD), nonkinisegenic (PNKD), and exercise induced (PED). There have been major advances in the understanding of the pathophysiological mechanisms and the genetics of these disorders, leading to better clinical definitions based on genotype-phenotype correlations in the familial idiopathic forms. PKD is genetically heterogenous, but there is linkage to chromosome 16 in a number of families. PNKD is due to mutations of the MR-1 gene. PED is genetically heterogenous, but a number of familial and sporadic cases may be due to GLUT-1 gene mutations. The GLUT1 gene-related form of PED may respond to a ketogenic diet. Potassium and calcium channel mutations underlie the 2 main forms of episodic ataxia (EA1 and EA2), whereas benign torticollis of infancy may also be a calcium channel disorder.

Dystonia update

PURPOSE OF REVIEW

Dystonia is a movement disorder with a complex and not fully understood pathophysiology. Its better understanding would enable more focused treatment for the disorder. In this review, we provide an overview of recent studies of the pathophysiology of primary and secondary dystonia, with an emphasis on functional brain imaging. Potential mechanisms underlying the beneficial effects of deep brain stimulation for dystonia are also summarized.

RECENT FINDINGS

The recognition of dysfunction at different levels of the nervous system has extended the classical notions of localized striatal abnormalities in primary dystonia. Recent biochemical studies have revealed evidence of abnormal torsion activity in DYT1 dystonia. Abnormal patterns of brain metabolism have also been identified using functional brain imaging in different dystonia genotypes. These findings, in conjunction with new electrophysiological techniques, can be utilized to help define a common mechanism for the neural dysfunction in dystonia.

SUMMARY

New insights into the pathophysiology of dystonia have been provided by recent studies using electrophysiology, biochemistry and human genetics, as well as functional brain imaging studies. These advances together may create the basis for new therapies for this disorder.