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Show The Ice Pack Test (or Ice Test) For Myasthenia Ryan D. Walsh, MD and Collin McClelland, MD Myasthenia gravis is an autoimmune disorder of neuromuscular transmission at the level of the neuromuscular junction. Variable, fatigable muscle weakness is the hallmark of myasthenia, with ptosis being a common manifestation (present in >90% of patients). Various tests are available for the diagnosis of myasthenia, including antibody testing (ex. anti-acetylcholine receptor antibodies, antimuscle specific kinase (MUSK) antibodies, anti-striated muscle antibodies), repetitive nerve conduction studies (assessing for decremental compound muscle action potential response to repetitive electrical stimulation), single fiber EMG (assessing for electrophysiologic signs of neuro-muscular junction dysfunction including abnormally-increased jitter or blocking), edrophonium (Tensilon) test, and the ice pack test (a.k.a. "ice test"). The ice pack test is a simple, low-tech, bedside test that can readily be applied in the outpatient clinic or hospital setting, with minimal risk or discomfort. The ice pack test is used in patients with ptosis to help support or refute a diagnosis of myasthenia. It has been observed that colder temperature can produce improved muscle function in myasthenic patients1. The exact mechanism by which cooling can improve myasthenic weakness is uncertain, however proposed mechanisms include enhanced release of acetylcholine, inhibition of acetylcholinesterase activity, and/or improved acetylcholine receptor sensitization. The ice pack test capitalizes on this temperaturebased differential in muscle function by comparing ptosis before and after the application of an ice pack to a ptotic superior eyelid. A positive ice pack test (i.e. ptosis improves following application of ice) is supportive of a diagnosis of myasthenia, while a negative test (i.e. ptosis does not improve following application of ice) makes myasthenia very unlikely. The ice pack test has a sensitivity of 0.92 (95% CI 0.62-1.00), specificity of 0.79 (95% CI 0.56-1.00), positive predictive value of 0.73 (95% CI 0.48-0.90), and negative predictive value of 0.94 (95% CI 0.70-1.00)2. To perform the ice pack test in a patient with ptosis, the following steps are employed: 1. Eyelid measurements are taken at baseline (particularly palpebral fissure height, and/or marginal reflex distance 1 (MRD1)); care should be taken to ensure that the measurements are taken in a resting state without activation of frontalis musculature-if necessary, gentle digital pressure can be applied to the frontalis muscle by the examiner while measurements are taken to avoid activation of the frontalis. 2. The patient is asked to keep his/her eyes closed while an ice pack is applied to the ptotic eyelid. This is left in place for 2-5 minutes while the patient rests comfortably. If there is bilateral asymmetric ptosis, the ice pack is typically applied to the more ptotic eyelid. 3. The ice pack is removed and the palpebral fissure height and/or MRD1 is re-measured immediately. 4. If there is more than 2 mm improvement in the palpebral fissure/MRD1 height, then the test is generally considered positive. It is not unusual to see dramatic transient improvement in ptosis with the ice test in patients with myasthenia (Figure 1). It is important to note that the sensitivity of the ice pack test decreases in patients with complete ptosis3. #12;Figure 1. Top: This patient with myasthenia is noted to have severe ptosis of the left upper eyelid at baseline. Middle: With both eyes closed, an ice pack is applied to the left eyelid for 5 minutes. Bottom: There is dramatic transient improvement in ptosis immediately following the ice pack test indicating a positive test. References 1. Sethi KD, Reivner MH, Swift TR. Ice pack test for myasthenia gravis. Neurology. 1987; 37: 1383-5. 2. Fakiri MO, Tavy DL, Hama-Amin AD, Wirtz PW. Accuracy of the ice test in the diagnosis of myasthenia gravis in patients with ptosis. Muscle Nerve. 2013; 48: 902-4. 3. Golnik KC, Pena R, Lee AG, Eggenberger ER. An ice test for the diagnosis of myasthenia gravis. Ophthalmology. 1999; 106: 1282-6. |
