Extraocular muscle responses to orbital cooling (ice test) for ocular myasthenia gravis diagnosis

Background: As a result of clinical and laboratory investigations of temper ature correlates of myasthenia gravis, orbital cooling (ice test) has been developed as a reliable test for ocular myasthenia diagnosis through blepha roptosis response. The test has not been utilized in a prospective manner f or myasthenia diagnosis through extraocular muscle responses. Methods: Fift een patients with acquired motility disorders were studied with the use of orbital cooling and other tests for myasthenia gravis. Orbital cooling was performed in a standard fashion for all patients. In 14 of 15 patients, the diagnosis of myasthenia was not established at the time the ice test was p erformed. Fifteen non-myasthenic patients with acquired motility disorders were also studied with use of the ice test, Temperatures during orbital coo ling were measured in the superior cul-de-sac of one patient and between th e lateral rectus muscle and globe in 3 patients. Results: All patients subs equently proven to have myasthenia gravis by other tests and by response to myasthenia therapy had a positive (diagnostic of myasthenia) response to t he ice test, No patient had a false-positive or a paradoxical response to t he ice test. No control patient had a positive blepharoptosis or motility r esponse to orbital cooling. Temperature measurements demonstrated significa nt cooling effects in the superotemporal cul-de-sac and beneath the lateral rectus muscles after orbital cooling for 5 minutes. Conclusions: Orbital c ooling, within certain parameters, can be a useful clinical test for myasth enia diagnosis through motility response, as well as blepharoptosis respons e.