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.