Decremental response on EMG is seen in
Myansthenia gravis
Lambert Eaton syndrome
Duschene muscular dystrophy
UMN lesion
Ans. is 'a' i.e., Myasthenia gravisDiagnosis of myaesthenia gravis 1Several special diagnostic Tests for mysthenia gravisElectrophysiological 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 offibres 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 anticholinesterase 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%Q sensitivity in ocular and 95% sensitivity in systemic myaesthenia.Measurement of receptor antibodies in the blood:* Measurement of antiacetylcholine receptor antibodies provides a sensitive and highly specific test for the diagnosis of myasthenia. Presence ofAch antibodies is virtually 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 diagnosis.Also knowMost specific test to diagnose myaesthenia gravis - Anti - AchR antibody test (presence of Anti - AchR antibody is virtuallyDiagnostic of myaesthenia gravis)Most sensitive test to diagnose myaesthenia gravis - Single fibre electromyography
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