Diagnosis of Myasthenia Gravis Confirmed with Tensilon Test

Post prepared by Dr Mrugesh Panchani, PGYIII Medicine Resident, Monmouth Medical Center.

For patients with clinical features and signs suggestive of myasthenia gravis, the Tensilon test can serve as an easy bedside confirmatory test.

Edrophonium (Tensilon) is an acetylcholinesterase inhibitor and we have already blogged about how these drugs can improve conduction across the neuromuscular junction in myasthenics.

cogan

Tensilon is preferable for diagnostic testing because of the rapid onset (30 s) and short duration (5 min) of its effect.

However, an objective end-point must be selected to evaluate the therapeutic effect, such as improvement in eye movements, ptosis, impairment of speech, or the length of time that the patient can maintain the arms in forward abduction.

Here’s a real life example (we have a signed consent form on file):

The first video shows our patient at her baseline with R>L ptosis and facial weakness:

Then the patient is given a low dose (2mg) of iv Tensilon (with telemetry monitoring and bedside atropine at the ready) is given and we see a definite improvement in ptosis and a more expressionful face:

This test was considered positive and hence terminated.

Had there been no change, the patient would have been given an additional 8 mg of iv Tensilon.

We typically start with a low dose at first because some patients react to edrophonium with side effects such as nausea, diarrhea, salivation, fasciculation, and (rarely) bradycardia. Atropine (0.6 mg) should be drawn up in a syringe, ready for IV administration if these symptoms occur.

Advertisements

Anisocoria (Unequal pupils)

The pupil is the hole in the center of the iris, that allows light to enter the retina. The iris is a thin strip of smooth muscle which regulates the amount of light entering the eye by controlling the size of the pupil.
pupil
The iris actually consists of two smooth muscles:  There is a circular group called the sphincter pupillae, which is innervated by the parasympathetic fibers that travel with the oculomotor nerve, and when activated constricts the pupil. There is also a radial muscle group called the dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, which when activated causes the pupil to dilate.

tumblr_lmyudzcUOp1qkpjw6o1_500

Anisocoria (unequal pupils) can be physiologic, or can result from a variety of disorders of the nervous system.

anisocoria

Anisocoria – the pupils are unequal, is the the pupil too large, or is the left pupil too small?

The first step in evaluating anisocoria is to determine which is the abnormal side – this can be accomplished by comparing the pupil sizes in response to bright light and dull ambient light:

horners, dark

If the smaller of the pupils is abnormal, a miosis, then the anisocoria will be more apparent (the affected pupil will be smaller) in dull ambient light conditions (a dark room), and less apparent (the pupils will be more equal) in bright light.

x

x

x

x

x

mydriosis

Alternatively, if the large pupil is the abnormal side, mydriasis, it will fail to contract in response to intense light.

x

x

x

x

x

x

Miosis (small pupil)

A unilateral miosis can be physiologic or can indicates a lesion affecting the sympathetic nerve fibers to the eye known as Horner’s syndrome.

Physiologic anisocoria is mild (usually less than 0.5 mm difference in size between the pupils, and the amplitude of the difference does not vary greatly under dim or bright light conditions.

Horner’s syndrome causes unilateral miosis, and the affected abnormal pupil either does not dilate or has a delayed dilation in the dark. Furthermore, there is usually an associated lid ptosis and facial hypohidrosis. Horner’s syndrome is important to diagnosis, because it can indicate a lesion in the brain stem (stroke), neck (carotid artery dissection) or lung apex (Pancoast’s tumor).

Horner pancoast

Right Horner’s syndrome (ptosis and miosis), from R apical lung tumor (Pancoast tumor).

xx

Mydriasis (Dilated Pupil)

This is most commonly caused by an anticholinergic drug, such as atropine or hyoscyamine, hyoscyamine, either from a medication, eye drop or misplaced nebulizer:

nebulizer, anisocoria

Unilateral mydriasis, caused by direct anticholinergic drug effect on iris because of a badly fitting face mask.

Damage or compression of the oculomotor nerve buy an aneurysm or brain herniation can also cause mydriasis, typically associated with ptosis and ophthalmoparesis:

R ptosis, occulomotor palsy (eye is deviated down and outwards), with a dilated pupil, caused by nerve compression from aneurysm (red arrow)

R ptosis, occulomotor palsy (eye is deviated down and outwards), with a dilated pupil, caused by nerve compression from aneurysm (red arrow)

Mydriasis from Adie’s Syndrome

Adie’s syndrome presents with abrupt onset mydriasis often associated with loss of deep tendon reflexes, thought to be the result of a viral infection that causes damage to neurons in the ciliary ganglion (the area of the brain that provides parasympathetic control of eye constriction). Clinical exam may reveal sectoral paresis of the iris sphincter or vermiform iris movements:

tonic pupil

Drooping eyelids (ptosis)

Ptosis can affect one or both eyes and results from weakness affecting the muscles that raise the eyelid.

L ptosis

Left sided ptosis

Ptosis can be congenital (you are born with it), or acquired (it develops during life).

Acquired ptosis can result from a variety of problems affecting the nerves, muscles, neuromuscular junction or tendons involved in elevating the eye lids.

Neurogenic ptosis is usually unilateral, and can be caused by a lesion affecting either the oculomotor nerve or the sympathetic nerve fibers to the eye (Horner’s syndrome).

When ptosis is caused by an oculomotor nerve lesion, there is  generally also some degree of eye movement abnormality (ophthalmoparesis).  Oculomotor nerve palsy can be caused by something as simple as diabetes, but if the nerve fibers to the pupil are involved (causing a dilated pupil in addition to the ptosis and ophthalmoparesis), that is very suggestive of a compressive lesion such as an aneurysm (see below) and warrants immediate evaluation.

R ptosis, occulomotor palsy (eye is deviated down and outwards), with a dilated pupil, caused by nerve compression from aneurysm (red arrow)

R ptosis, oculomotor palsy (eye is deviated down and outwards), with a dilated unreactive pupil, caused by nerve compression from aneurysm (red arrow)

Horner’s syndrome causes mild ptosis associated with a small pupil (miosis) sometimes associated with lack of sweating (anhidrosis) on the face, and can be caused by trauma to the carotid artery, lung tumors, or strokes.

L Horner's syndrome with mild ptosis and miosis

L Horner’s syndrome with mild ptosis and miosis

Myasthenia gravis is an autoimmune disease that affects the neuromuscular junction, and frequently presents with fatiguable ptosis often associated with double vision and limb weakness.   The ptosis will usually get worse when the patients is tired at the end of the day (diurnal variation):

Fatiguable ptosis in myasthenia gravis

Fatiguable ptosis in myasthenia gravis

The ptosis of myasthenia can be temporarily improved with an acetylcholinesterase inhibitor medication, such as an injection of edrophonium (Tensilon), and this can used a diagnostic test.

Ptosis can also be seen in certain muscle diseases, including oculopharyngeal muscular dystrophy, mitochondrial myopathy and myotonic dystrophy.

Bilateral ptosis in a patient with myotonic muscular dystrophy

Bilateral ptosis in a patient with myotonic muscular dystrophy

However, acquired ptosis is most commonly caused by dehiscence or disinsertion of the levator aponeurosis, causing a disconnection between the eye lid and the elevating muscles.

This usually occurs in elderly patients, but can sometimes affect younger contact lens users.

L ptosis from levator dehiscence - Note that when the eye is closed, the lid crease is fainter and further away from the lid margin in the left eye, compared to the right eye

L ptosis from levator dehiscence – Note that when the eye is closed, the lid crease is fainter and further away from the lid margin in the left eye, compared to the right eye

Patients who notice a drooping eyelid, unequal pupils, or double vision should consult with a neurologist in order to establish the correct diagnosis.

After that, treatment might include medical therapy for an underlying disorder (such as diabetes or myasthenia), surgery or even eye lid crutches:

Myasthenic patient with isolated L ptosis, demonstrating improvement with the eye lid "crutch"

Myasthenic patient with isolated L ptosis, demonstrating improvement with the eye lid “crutch”