Ice pack test—an useful bedside test to diagnose myasthenia gravis

Case presentation

A 35-year-old gentleman with no past illness presented to a district hospital with acute onset type 2 respiratory failure. He presented with worsening dyspnoea for 1 day and decreased conscious level on arrival to emergency department. His Glasgow Coma Scale was E2V2M3. He was intubated for airway protection. His arterial blood gas showed pCO2 62.7 mmHg, pO2 409 mmHg, pH 7.2 and HCO3 24 mmol/l.

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Two days later, patient regained consciousness after his sedation was off and was able to communicate. He was noted to have bilateral ptosis. History from patient revealed generalized body weakness, diplopia and dysphagia for 1 month. Examination noted complex opthalmoplegia, positive fatigability test, proximal muscle weakness with normal sensation and reflexes. His ice pack test was positive (Figures 1 and 2).

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He was treated as myasthenia crisis with intravenous immunoglobulin and high dose steroid. He managed to be extubated after a period of ventilation and supportive care. He was eventually discharged well. His acetylcholine receptor antibodies came back positive with titre of >8.4 nmol/l. Repetitive nerve stimulation was not done due to unavailability of the test in the centre. His computed tomography of thorax showed presence of thymoma.

Myasthenia gravis is an autoimmune disorder, which affects the neuromuscular junction. The hallmark of the disease is presence of fatigable muscle weakness with ptosis. In the severe form of illness, it can present as myasthenia crisis where there is severe bulbar and respiratory weakness that requires mechanical ventilation.1

Diagnosis of myasthenia gravis is often challenging especially in an intubated patient. Bedsides clinical tests that can be done are tensilon test and ice pack test. Other investigations that can be done are acetylcholine receptor antibody, repetitive nerve stimulation, but these tests are not easily available. Tensilon test is not commonly done nowadays due to its potential serious cardiac side effects.

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Ice pack test derived from clinical observations that cold improves myasthenia symptoms whereas heat worsens it.2 Neuromuscular transmission improves at lower temperature. These observations were reported by Simpson and Guttman in the past. The exact mechanism behind this is still uncertain. Postulated theories include cold enhanced release of acetylcholine, inhibition of acetylcholinesterase activity and/or improved acetylcholine receptor sensitization.

Ice pack test can be done by taking baseline eyelid measurement. Ice pack is then applied for 2-5 min and the eyelid is re-measured after that. If there is improvement of 2 mm or more, it’s considered a positive test.3 The test is thought to be sensitive and specific for myasthenia gravis, where it has no effect on ptosis from other causes. The reported sensitivity is up to 80%.4 In conclusion, ice pack test is a very useful bedside test when myasthenia gravis is suspected as its safe, cheap and easily performed.

Conflict of interest: None declared.