OCULAR NEUROMYOTONIA

Aims/Background-Ocular neuromyotonia is characterised by spontaneous s pasm of extraocular muscles and has been described in only 14 patients . Three further cases, two with unique features, are described, and th e underlying mechanism reviewed in the light of recent experimental ev idence implicating extracellular potassium concentration in causing sp ontaneous firing in normal and demyelinated axons. Methods-Two patient s had third nerve neuromyotonia, one due to compression by an internal carotid artery aneurysm, which has not been reported previously, whil e the other followed irradiation of a pituitary tumour, a common assoc iation in the published reports. Selective activation occurred in both , where neuromyotonic activity was triggered by prolonged voluntary ac tivation of specific extraocular muscles with Or without spread of act ivity to other third nerve muscles. The other patient had fourth nerve involvement, where spasms of the superior oblique muscle were induced only by alcohol, a phenomenon which has not been described. Results-T he two patients with third nerve involvement responded to carbamazepin e and in one, an improvement in a chronic partial third nerve paresis occurred. The other has not required treatment and remains asymptomati c by refraining from alcohol. Conclusions-A careful examination, inclu ding the effects of prolonged voluntary muscle action is required to i nitiate episodes and to demonstrate selective activation. Imaging is m andatory to exclude compressive intracranial lesions, particularly whe re there is no history of pituitary fossa irradiation. A trial of anti -convulsants should be considered in all patients. Extracellular potas sium may play a role in spontaneous firing and ephatic transmission in ocular neuromyotonia.