Clinical details are given of different types of
episodic ataxia: type 1, with
myokymia, and attacks which usually last a few minutes, and may occur several times a day, and treatment with
acetazolamide can reduce the number of attacks; type 2, with interictal nystagmus, and attacks which last for several hours to a day or more, and treatment with
acetazolamide is very effective; paroxysmal choreoathetosis with
episodic ataxia, with attacks lasting for about 20 min and occurring at varying intervals; and
familial hemiplegic migraine, with
transient hemiplegia presenting during the
aura of a
migraine headache, the symptoms improving on treatment with
acetazolamide. Their inheritance is of dominant type; and the gene for type 1 is mapped to chromosome 12p near to a cluster of
potassium channel genes, and that for type 2 and for
familial hemiplegic migraine to chromosome 19p near to
calcium channel genes. The differential diagnosis from other conditions with a periodic symptomatology is discussed, especially from a number of metabolic disorders. Treatment is effective for many of these, and the treatment of the episodic
ataxias with
acetazolamide can sometimes have a dramatic effect. The possible role of the
channelopathies in the causation of some periodic
neurological disorders is considered; with the expectation that further research will improve the identification of specific diseases, and lead to more effective treatment.