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

Background:As a result of clinical and laboratory investigations of temperature correlates of myasthenia gravis, orbital cooling (ice test) has been developed as a reliable test for ocular myasthenia diagnosis through blepharoptosis response. The test has not been utilized in a prospective manner for myasthenia diagnosis through extraocular muscle responses.

Methods:Fifteen 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 performed. Fifteen non-myasthenic patients with acquired motility disorders were also studied with use of the ice test. Temperatures during orbital cooling were measured in the superior cul-de-sac of one patient and between the lateral rectus muscle and globe in 3 patients.

Results:All patients subsequently proven to have myasthenia gravis by other tests and by response to myasthenia therapy had a positive (diagnostic of myasthenia) response to the ice test. No patient had a false-positive or a paradoxical response to the ice test. No control patient had a positive blepharoptosis or motility response to orbital cooling. Temperature measurements demonstrated significant cooling effects in the superotemporal cul-de-sac and beneath the lateral rectus muscles after orbital cooling for 5 minutes.

Conclusions:Orbital cooling, within certain parameters, can be a useful clinical test for myasthenia diagnosis through motility response, as well as blepharoptosis response.