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Tensilon Test

This test involves careful observation of the patient after I.V. administration of Tensilon (edrophonium chloride), a rapid, short-acting anticholinesterase that improves muscle strength by increasing muscle response to nerve impulses.

Purpose

  • To aid diagnosis of myasthenia gravis (results of other procedures, including electromyography, may supplement Tensilon test findings)
  • To aid in differentiation between myasthenic and cholinergic crises
  • To monitor oral anticholinesterase therapy

Patient preparation

  • Explain to the patient that this test helps determine the cause of muscle weakness.
  • Describe the test, including who will perform it and where and its duration (15 to 30 minutes).
  • Don't describe the exact response that will be evaluated; foreknowledge can affect the test's objectivity.
  • Explain to the patient that a small tube will be inserted into a vein in his arm and that a drug will be administered periodically. He'll be asked to make repetitive muscle movements and his reactions will be observed. To ensure accuracy, the test may be repeated several times.
  • Advise him that Tensilon may produce some unpleasant adverse effects, but reassure him that someone will be with him at all times and that any reactions will quickly disappear.
  • Check the patient's history for medications that affect muscle function, anticholinesterase therapy, drug hypersensitivities, and respiratory disease. Withhold medications. If the patient is receiving anticholinesterase therapy, note this on the requisition slip; include the time of the most recent dose.

Equipment

Standard: 10 mg Tensilon, 0.4 mg atropine (may be prescribed for patients with respiratory distress), one tuberculin and one 3-ml syringe, I.V. infusion set, 50-ml bag of I.V. solution (dextrose 5% in water [D5W] or normal saline solution), tape, tourniquet, alcohol swabs.

Emergency: 0.5 to 1.0 mg atropine I.V. for cholinergic crisis, 0.5 to 2.0 mg neostigmine methylsulfate I.V. for myasthenic crisis (may be repeated up to a total of 5 mg), extra tuberculin and 3-ml syringes (for atropine or neostigmine injections), resuscitation equipment, including a tracheotomy tray.

Procedure and posttest care

  • Begin an I.V. infusion of D5W or normal saline solution.
  • When performing the test on an adult patient suspected of having myasthenia gravis, 2 mg of Tensilon are administered initially. Before the rest of the dose is administered, the doctor may want to fatigue the muscles by asking the patient to perform various exercises, such as looking up until ptosis develops, counting to 100 until his voice diminishes, or holding his arms above his shoulders until they drop. When the muscles are fatigued, the remaining 8 mg of Tensilon are administered over 30 seconds.
  • The test may begin with a placebo injection to evaluate the patient's muscle response more accurately. The placebo isn't necessary if cranial muscles are being tested because cranial strength can't be simulated voluntarily.
  • After Tensilon is administered, the patient is asked to perform repetitive muscle movements, such as opening and closing his eyes and crossing and uncrossing his legs. Closely observe the patient for improved muscle strength. If muscle strength doesn't improve within 3 to 5 minutes, the test may be repeated.
  • To differentiate between myasthenic crisis and cholinergic crisis, 1 to 2 mg of Tensilon is infused. After infusion, continually monitor the patient's vital signs. Watch closely for respiratory distress, and be prepared to provide respiratory assistance.
  • If muscle strength doesn't improve, more Tensilon is infused cautiously, 1 mg at a time up to a maximum of 5mg, and the patient is observed for distress.
  • Neostigmine is administered immediately if the test demonstrates myasthenic crisis; atropine is administered for cholinergic crisis.
  • To evaluate oral anticholinesterase therapy, 2 mg of Tensilon is infused 1 hour after the patient's last dose of the anticholinesterase. The patient is observed carefully for adverse effects and muscle response.
  • After Tensilon administration, the I.V. line is kept open at a rate of 20 ml/ hour until all the patient's responses have been evaluated.
  • When the test is complete, discontinue the I.V., and check the patient's vital signs.
  • Check the puncture site for hematoma, excessive bleeding, and swelling.
  • Tell the patient to resume any medications withheld for the test.
Precautions
  • Because of the systemic adverse reactions Tensilon may produce, this test may be contraindicated in patients with hypotension, bradycardia, apnea, and mechanical obstruction of the intestine or urinary tract.
  • Patients with respiratory ailments such as asthma should receive atropine during the test to minimize adverse reactions to Tensilon.
  • Stay with the patient during the test, and observe him closely for adverse reactions.
  • Keep resuscitation equipment handy in case of respiratory failure.
Normal findings

People who don't have myasthenia gravis usually develop fasciculation in response to Tensilon. The doctor must interpret the responses carefully to distinguish a normal person from one with myasthenia gravis.

Abnormal findings

If the patient has myasthenia gravis, muscle strength should improve promptly after administration of Tensilon. The degree of improvement depends on the muscle group being tested; improvement is usually obvious within 30 seconds. Although the maximum benefit lasts only several minutes, lingering effects may persist ­up to 2 hours in a patient receiving prednisone, for example. All patients with myasthenia gravis show improved muscle strength in this test; some patients respond slightly and the test may need to be repeated to confirm the diagnosis.

The test may yield inconsistent results if myasthenia gravis affects only ocular muscles, as in mild or early forms of the disorder. It may produce a positive response in motor neuron disease and in some neuropathies and myopathies. The response is usually lessdramatic and less consistent than in myasthenia gravis.

Patients in myasthenic crisis show brief improvement in muscle strength after Tensilon administration. Patients in cholinergic crisis (anticholinesterase overdose) may experience exaggerated muscle weakness. If Tensilon increases the patient's muscle strength without increasing adverse effects, oral anticholinesterase therapy can be increased. If Tensilon decreases muscle strength in a person with severe adverse reactions, therapy should be reduced. If the test shows no change in muscle strength and only mild adverse effects occur, therapy should remain the same.

Interfering factors
  • Prednisone (possible delay of Tensilon's effect on muscle strength)
  • Quinidine and anticholinergics (inhibit the action of Tensilon)
  • Procainamide and muscle relaxants (inhibit normal muscle response)

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