Decremental response on EMG is seen in

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