What is Tensilon Test?

The Tensilon Test, also known as the Edrophonium Chloride Test, is a bedside tool for the diagnosis of myasthenia gravis. Myasthenia gravis is an autoimmune disorder characterized by reduced concentration of acetylcholine receptors. This results in muscle weakness and fatigability, which is worsening weakness after use. The ocular muscles, which are responsible for eye movements, and the levator palpebrae, which is present in the eyelid, are most commonly involved. Weakness of the levator palpebrae causes ptosis, which is drooping of the eyelid. The administration of edrophonium improves this weakness by increasing the concentration of acetylcholine in the neuromuscular junction. The test can be performed on the eyelid, ocular, pharyngeal, or limb muscles, though the last one is dependent on patient effort. The eyelid muscle is most ideal if the patient has ptosis.

Indications for performing the Tensilon Test:

• Diagnosis of myasthenia gravis
• Differentiating myasthenic crisis from cholinergic crisis caused by excess cholinesterase inhibitors
• Differentiating myasthenia from Eaton Lambert syndrome, where the improvement in strength is not as remarkable as in myasthenia

How is the Tensilon Test performed?

• An intravenous access is first procured
• The patient is asked to look upwards for as long as possible. This typically causes fatigable ptosis (droopiness of the eyelid with sustained elevation) in a myasthenic patient
• The time eyelid starts drooping is recorded
• Edrophonium chloride is administered intravenously
• The patient is asked to repeat the step after a period
• The same process is repeated increasing the dosage of edrophonium 
• There is a limit on the maximum dose that can be administered
• The process is terminated earlier if there is an improvement in the duration for which the patient can hold up his/her eyelids

Improvement of ptosis within a minute of administering the edrophonium is considered a positive test. The Tensilon Test is positive in over 90% of patients with myasthenia gravis. Other conditions with neuromuscular pathology that can respond to edrophonium include motor neuron diseases, such an amyotrophic lateral sclerosis (ALS), and diseases of the oculomotor nerves. The results should be corroborated with other tests for myasthenia gravis, such as acetylcholine receptor antibody titers and electromyography (EMG). Side effects from edrophonium include excess lacrimation, salivation, sweating, low heart rate, hypotension, bronchospasm, and abdominal cramping. Atropine can mitigate these effects. Neostigmine administered intramuscularly is an alternative, especially in younger children.