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|Year : 2016 | Volume
| Issue : 6 | Page : 1173-1174
Ice test in the diagnosis of myasthenic ptosis
Department of Neurology, Paras Hospitals, Gurgaon, Haryana, India
|Date of Web Publication||11-Nov-2016|
Department of Neurology, Paras Hospitals, Gurgaon, Haryana
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Gupta M. Ice test in the diagnosis of myasthenic ptosis. Neurol India 2016;64:1173-4
Myasthenia gravis (MG) is an autoimmune disorder of the neuromuscular junction transmission. It is caused by antibodies targeting the skeletal muscle nicotinic acetylcholine receptors (AChR), muscle specific kinase (MuSK), and some undefined antigens, LRP4 and agrin, that affect neuromuscular transmission. It is characterized by fluctuating weakness or fatigability of skeletal muscles. MG is differentiated into two major clinical forms, namely, ocular MG (OMG) and generalized MG (GMG).
The disease has a predilection for ocular muscles – the levator palpebrae superioris complex that elevates the eye lid and the extraocular muscles (EOMs) that move the globe. The twitch fibers in EOMs develop tension faster and have a higher frequency of synaptic firing than limb muscles. This makes them more susceptible to fatigue. The tonic muscle fibers that sustain the gaze in any direction have fewer AChR, making them more susceptible to receptor loss and damage. All patients show ocular involvement during the course of the disease, whereas the disease remains restricted to the ocular muscles in a few patients (15–17%). It has been reported that 82% of the patients with OMG would develop GMG in the first 2 years after diagnosis. Age, AChR antibody titers, and thymoma are postulated to affect the conversion rates. There is some evidence that immunosuppression might prevent the conversion to generalized myasthenia in 75% of the patients with OMG.
Generalized and ocular myasthenia differ with respect to the demographics of the adult population. More female patients compared to males, in a ratio of 3:2, are affected with generalized myasthenia, whereas more males above the age of 40 years are affected by ocular myasthenia.
More than 75% of MG patients present with ptosis or diplopia. OMG can mimic any painless, pupil sparing, ocular motility disorder. The motility deficit may not follow any particular pattern. The deviation is more often incomitant than comitant. Involvement of orbicularis oculi is consistently present, manifesting as weakness in forceful closure of the eyes against resistance. With prolonged lid closure, the lids may spontaneously open (peek sign). OMG can mimic 3rd, 4th, and 6th cranial nerve palsies, gaze palsies, internuclear ophthalmoplegia, blepharospasm, and skew deviation. Senile ptosis and levator dehiscence can be differentiated owing to lack of fluctuation. Progressive external ophthalmoplegia produces symmetric ptosis and ophthalmoparesis with slow saccades. Horner's syndrome is differentiated by miosis and elevation of the lower lid.
Variable ptosis is the most common manifestation of MG because of the involvement of levator palpebrae superioris complex. It may be unilateral or bilateral. In the case of bilateral manifestation, it is often asymmetrical. Ptosis may increase after a prolonged upgaze movement or after repeated eyelid closure, referred to as the “lid fatigability test.” In case of unilateral ptosis, there may be hyperretraction of the lid of the other eye, and when the ptotic lid is manually elevated, the retracted lid droops as per the Herring's law of equal innervations. The lid twitch is elicited by asking the patient to change gaze from the downward direction to the primary position. The lid is seen to overshoot in a twitch before gaining its initial ptotic position (sensitivity and specificity of this clinical test is low).
In addition to clinical evaluation, the tests performed to confirm the diagnosis of MG are the edrophonium test (tensilon), repetitive nerve stimulation (RNS), single fiber electromyography (EMG), and estimation of serum acetylcholine receptor (AChR) antibodies. The edrophonium test has been considered the diagnostic test. However, false positive tests have been reported in amyotrophic lateral sclerosis and botulism. It also carries a risk of serious cardiac reactions. In pure ocular disease, the sensitivity of the edrophonium test is approximately 86%. The diagnostic yield of RNS and AChR antibodies in ocular myasthenia is quite low (56–70%). The most sensitive test for myasthenia is single fiber EMG and the yield is up to 80% for ocular and 95% for generalized myasthenia. However, its specificity is low, the test is expensive, needs expertise, and is not widely available.
Ice pack, rest, and sleep tests are nonpharmacological evaluations, Prism measurements and margin reflex distance should be documented in patients who have ptosis and/or diplopia. This should be accompanied by a facial photo on a cell phone camera. For the rest test, the patient is asked to close his/her eyes for 5 minutes, and then the improvement in ptosis is measured. For the sleep test, the patient is asked to lie down with eyes closed for 30 minutes in a quiet, dark room. Then, the improvement in ptosis and ophthalmoparesis is assessed.
Exacerbation and relief in myasthenic symptoms related to warming and cooling of the environmental temperatures were described in several articles published between 1960 and 1980. Orbital cooling with an ice pack was described as a test for ocular myasthenia in 1979 and has been proven to be valid for myasthenic ptosis.
The ice pack test is a simple, safe, and cheap procedure. It consists of application of ice to the eyes for 2 minutes, ensuring that the eyes are covered to prevent burns. If positive, the ptosis is cleared. If ice is kept for long, the procedure becomes uncomfortable and reduction in the muscle fiber temperature below 22°C reduces the contractile force of the muscle leading to a false negative result. The results are deemed positive if there is a raise of 2 mm or more of the palpebral fissure on removal of the ice pack. There are no randomized and controlled studies to validate it, but the test is both sensitive and specific. Its sensitivity ranges 80–100%, and its specificity is very high, considering that it is not positive in other diseases simulating myasthenic ptosis. In a large study, 156 patients with ptosis were subjected to Tensilon test and ice pack test. In 61 patients with a positive Tensilon test, the ice test was positive; and, in none of the 95 patients with a negative Tensilon test, was the ice test positive. Improvement in ptosis by cooling is possibly due to inhibition of acetylcholinesterase providing increased amount of actylcholine in the synaptic cleft.
Why the ice pack test is so underutilized? Possibly, in most instances, it has not been done properly. The ice pack test does have some drawbacks as it is not useful in ocular myasthenia where there is no ptosis or when there is complete ptosis. The ice pack test is a useful bedside test for myasthenic ptosis. It is rapid, simple, and inexpensive with a high degree of specificity and sensitivity; it is also applicable where the use of anticholinestrase agents is contraindicated by the cardiac status or age of the patient.
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Tabassi A, Dehghani A, Saberi B. The ice test for diagnosing myasthenia gravis. Acta Medica Iranica 2005;43:60-2.
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