EPISODIC ATAXIA AND CHANNELOPATHIES

Clinical details are given of different types of episodic ataxia: type 1, with myokymia, and attacks which usually last a few minutes, and m ay occur several times a day, and treatment with acetazolamide can red uce the number of attacks; type 2, with interictal nystagmus, and atta cks which last for several hours to a day or more, and treatment with acetazolamide is very effective; paroxysmal choreoathetosis with episo dic ataxia, with attacks lasting for about 20 min and occurring at var ying intervals; and familial hemiplegic migraine, with transient hemip legia presenting during the aura of a migraine headache, the symptoms improving on treatment with acetazolamide. Their inheritance is of dom inant type; and the gene for type 1 is mapped to chromosome 12p near t o a cluster of potassium channel genes, and that for type 2 and for fa milial hemiplegic migraine to chromosome 19p near to calcium channel g enes. The differential diagnosis from other conditions with a periodic symptomatology is discussed, especially from a number of metabolic di sorders. Treatment is effective for many of these, and the treatment o f the episodic ataxias with acetazolamide can sometimes have a dramati c effect. The possible role of the channelopathies in the causation of some periodic neurological disorders is considered; with the expectat ion that further research will improve the identification of specific diseases, and lead to more effective treatment. (C) 1998 Elsevier Scie nce B.V.