21 year old female presents with history of mild bilateral ptosis, proximal muscle weakness and easy fatiguability which among the following is best in diagnosing this condition aEUR’
Correct Answer: Edrophonium test
Description: Edrophonium test [Ref: Harrison 17th/e p. 2674; 16 /e p. 2520; Kanski 5th/e p. 6541 Occular involvement, proximal muscle weakness and easy fatiguability points towards myasthenia gravis. Diagnosis of myaesthenia gravis Several special diagnostic Tests for mysthenia gravis Electrophysiological Testing : (Repetitive nerve stimulation test) * Characteristic of myasthenia on electrophysiological testing is rapid reduction in the amplitude of muscle action potentials evoked during a series of repetitive stimulations of a peripheral nerve at a rate of 3 per second (decrementing response) * The traditional and simple method is to stimulate the nerve at 3 Hz and to measure the compound muscle action potential (a decrement of more than 10% when comparing the fifth to the first response is abnormal) Single fibre electromyography * This is more sensitive but technically more difficult than electrophysiological testing * Confirmatory but not specific. * This technique demonstrates an inconstancy in the firing of fibres connected to the same motor unit or a blocking of successive discharges from single muscle fibre belonging to the same motor unit. Edrophonium and Neostigmine test/Tensilon test * When edrophonium and neostigmine are given intravenously, it produces a transient improvement in strength in patients with myasthenia. * Edrophonium and neostigmine are anti cholinesterase so they prolong and exaggerate the effect of acetylcholine in the synapse and therefore provide an increment in muscle power in patient with myasthenia, * It is highly sensitive with 85%2 sensitivity in ocular and 95%e sensitivity in systemic myaesthenia. Measurement of receptor antibodies in the blood: ... * * Measurement of antiacetylclzoline receptor antibodies provides a sensitive and highly specific test for the diagnosis of myasthenia. Presence of Ach antibodies is viually diagnostic of Myaesthenia graves. * Sensitivity is limited to about 50% in purely occular myasthenia and about 85% in generalized myasthenia. * Definitive if positive but negative test does not rules out the diagnosisdeg. The question has specifically asked which test would be most useful "to diagnose" myaesthenia gravis. The electrophysiological tests such as EMG and repetitive nerve stimulation test are quite sensitive test used for the diagnosis of myasthenia gravis, but they are not diagnostic. Abnormality in these tests denotes some defect in neuromuscular conduction. It does not mean that these neuromuscular conduction defects are due to myasthenia gravis. Edrophonium test is more diagnostic than electrophysiological test for the diagnosis of myasthenia gravis. Also know Most specific test to diagnose myaesthenia gravis Anti - AchR antibody test (presence of Anti - AchR antibody is viually Diagnostic of myaesthenia gravis) Most sensitive test to diagnose myaesthenia gravis Single fibre electromyography
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