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

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.

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.

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.

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