By Year 4th Elective Medical Student
Myasthenia gravisMyasthenia gravisMyasthenia gravis (MG) is the most frequent
neuromuscular transmission disorderpathophysiology is autoimmune with
acetylcholine receptors (AChR) autoantibodies damaging the post-synaptic fold at the muscle membrane
often presents with isolated ocular symptoms, including diplopia and ptosis
Other clinical features include bulbar symptoms (dysphagia, dysarthria), proximal limb muscles weakness and fatigue
Main characteristic of the MG is the fluctuating weakness during the day, being milder during the morning and more severe at the evening
Physical activity usually worsens the weakness
Edrophonium testThe most traditional bedside diagnostic test for
myasthenia gravis is the edrophonium test. It has been considered diagnostic of MG in the past, however false-positive results have been reported in other neurologic disorders like amyotrophic lateral sclerosis, botulism and brain tumor
Furthermore, it carries a risk of serious cardiac adverse reations such as bradycardia and chest pain
Its sensitivity is about 86% in pure ocular disease
The most sensitive test for ocular myasthenia is single fiber EMG, reaching up to 80% in pure ocular cases and 95% in generalized disease
However its specificity is low, the test is expensive
Ice pack testVery simple, safe and cheap procedure that
can be performed by the physician at the bedside
Does not require medications or expensive equipment and is free of adverse effects
It consists of the application of an ice pack on the patient symptomatic eye for 2 minutes
The response is positive when there is improvement of the ptosis (increase in at least 2 mm of the palpebral fissure from before to after the test)
It is widely known that warm temperatures worsen MG symptoms and cooling is able to improve them
The improvement of MG with cooling probably occurs by lesser acetylcholinesterase activity in temperatures below 280C, providing increasing amount of ACh molecules in the synaptic cleft
Today, we will find sensitivity and spectivity of the ice pack test
Ice Pack TestIce Pack Test Disease Test
Positive Negative Total
Positive 5 0 5
Negative 1 6 7
Total 6 6 12
Ice Pack TestIce Pack Test
Sensitivity = 5/ 6 x100 = 83.33%
Specificity = 6/6 x 1 00 = 100%
Ice Pack Test VS Enhancing PtosisIce Pack Test VS Enhancing Ptosis
Patient
SexEnhancing ptosis
Ice pack test
Eye opening duration (min)
1.Femal
ePositive Positive 1.0
2.Femal
ePositive Negative 0
3.Femal
ePositive Positive 1.30
4.Femal
ePositive Positive 1.0
5.Femal
ePositive Positive 1.20
6. Male Positive positive 3.30
Enhanced ptosis Observed in patients with some initial ptosis .
The patient looks straight ahead and refrains from blinking . The examiner holds one eye open, which results in the other lid starting to droop more
Hering's law of equal innervation applies to eyelid muscles, which are innervated by a single midline brainstem nucleus providing equal bilateral central output . In unilateral ptosis, excessive innervational stimulation often causes the contralateral eyelid to appear retracted
If ptosis is bilateral but asymmetric, the less affected eyelid may appear normal
Enhanced Ptosis TestEnhanced Ptosis Test Disease Test
Positive Negative Total
Positive 6 0 6
Negative 0 6 6
Total 6 6 12
Enhanced Ptosis TestEnhanced Ptosis Test
Sensitivity = 6/ 6
x100 = 100% Specificity = 6/6 x 1
00 = 100%
Ice Pack Test VS Enhancing PtosisIce Pack Test VS Enhancing Ptosis
Mean eye opening duration of ice pack test = 500/5 = 100 secs = 1.40 mins
SummarySummary
Both enhancing ptosis and ice pack test have adequate sensitivity in patient with Myasthenia Gravis.
Both tests are simple and easy to do.
Patients can do their own ice pack when they get worsening ptosis.