Ice Pack Test
The ice pack test is performed by holding an ice cube, wrapped in a towel or a surgical glove, over the levator palpebrae superioris muscle of a ptotic eye for 2-10 minutes. Improvement of ptosis is said to be specific for myasthenia gravis: cold improves transmission at the neuromuscular junction (myasthenic patients often improve in cold as opposed to hot weather). This phenomenon is not observed in other causes of ptosis. A pooled analysis of several studies gave a test sensitivity of 89% and specificity of 100% with correspondingly high positive and negative likelihood ratios. The test is easy to perform and without side effects (cf. Tensilon test).
Whether the ice pack test is also applicable to myasthenic diplopia has yet to be determined. False positives have been documented.
Larner AJ. The place of the ice pack test in the diagnosis of myasthenia gravis. International Journal of Clinical Practice 2004; 58: 887-888 Larner AJ, Thomas DJ. Can myasthenia gravis be diagnosed with the "ice pack test"? A cautionary note. Postgraduate Medical Journal2000; 76: 162-163