The Mechanism of Action of Quinine in Myotonia and Myasthenia

Wolf1was the first to point out the ability of quinine to relieve the difficulty in the muscular relaxation of patients with myotonia congenita and myotonic dystrophy. Later Kennedy and Wolf2commented on the increase in muscular weakness produced in patients with myasthenia gravis by the administration of quinine and, conversely, the increase in the degree of myotonia after the administration of prostigmine. These observations were fully corroborated by Kolb and his associates,3who suggested that prostigmine would be of value when diagnosis was difficult, as in the condition described by Curschmann4of myotonia sine myotonia. These authors also observed that small amounts of prostigmine could completely counteract the beneficial effect of quinine in myotonia, even when large doses of the latter drug were used. Harvey and Whitehill5had previously discussed the value of quinine in the diagnosis of early cases of myasthenia gravis, when