Purpose: To investigate the diagnostic value and to establish threshold criteria for the ice pack test as an office preliminary test in the differential diagnosis of myasthenic diplopia in comparison with blepharoptosis.
Design: Prospective, comparative cohort study.
Participants: Eighty-nine patients with a recent onset of diplopia, blepharoptosis, or both were evaluated with orbital cooling in a prospective manner. Forty-eight patients presented with diplopia, 25 patients with both blepharoptosis and ophthalmoplegia and 16 patients with blepharoptosis.
Testing: All patients had the ice pack applied for 5 minutes on both eyelids at the initial orthoptic evaluation. Increasing the duration of cooling to 10 minutes was investigated in 36 diplopic patients. A complete diagnostic work-up was ordered and patients were followed up for a minimum of 6 months before diagnosis of myasthenia gravis was ascertained.
Main outcome measures: Difference in cover test measurements in primary position or marginal reflex distance before and after the application of the ice pack, specific cause for diplopia and blepharoptosis.
Results: Fifteen patients were diagnosed as myasthenic. The optimal cutoff point for a positive response to the ice pack test proved to be a reduction in ocular deviation in primary position by 50% or by 10 prism diopters (PD) or more for presenting deviations larger than 20 PD. By this criterion, sensitivity for the detection of myasthenic diplopia was 76.9% (95% confidence interval [CI], 49.06%-92.50%) for the 5-minute application, compared with 92.3% (95% CI, 63.5%-98.9%) sensitivity demonstrated for blepharoptosis. Increasing the time of application to 10 minutes did not improve the diagnostic value of the test. Specificity was high (98.3%; 95% CI, 90.3%-99.9%) and was demonstrated even in patients with coexisting myasthenic and dysthyroid ophthalmopathy. Patients with oculomotor nerve paresis and Horner syndrome invariably were nonresponsive to the test.
Conclusions: The ice pack test demonstrated high specificity and an acceptable sensitivity in the differential diagnosis of myasthenic diplopia. Data from this series suggest that a partial rather than a complete response to the ice pack test may be expected for myasthenic diplopia. Standardization of the method of application of the ice pack is critical for the interpretation of its effect.