The most sensitive test for the diagnosis of myasthenia Gravis is
Answer is D (Single Fiber Electromyography (SFEMG)) : Single Fiber Electromyography (SFEMG) is the single most sensitive assay of neuromuscular function dysfunction in myasthenia gravis `SFEMG is the single most sensitive assay of neuromuscular function dysfunction in myasthenia gravis having a sensitivity of greater than 95% when applied to clinically affected muscle' - Merrit's Neurology 12th(2009) /389 `Single fiber electromyography is the most sensitive diagnostic test for MG, but abnormalities are not specific'. - 'Neuromuscular Junction Disorders: Diagnosis & Treatment (2003)/109 `Single fiber EMG is the most sensitive electrophysiological test for myasthenia gravis' - Adult Neurology' 2nd (Blackwell publishing) /299 Taken from 'Neuromuscular Junction Disorder's: Diagnosis & Treatment (2003) /109 Edrophonium test / Tensilon test Highly sensitive test with 85% sensitivity in ocular and 95% sensitivity in systemic myasthenia -Kanski Diagnosis is highly probable if test in unequivocally positive An initial dose of 2mg of edrophonium is given intravenously. If improvement occurs the test is considered positive and terminated. If there is no change an additional 8mg are given intravenously . Acetylcoline Receptor antibodies Sensitivity of 80-90% in systemic myasthenia - CMDT Highly specific and presence of Anti ACH Receptor Antibodies is viually diagnostic of M. gravis 85% positive in generalized M.G. 50% positive in ocular M.G. Definitive if positive Negative test does not exclude M.G. 40% of Anti antibody negative patients have Anti-Musk antibodies. Repetitive nerve stimulation / Electrodiagnostic test Helpful diagnostic evidence Best when weak muscles/ proximal ms. groups are tested Amplitude of evoked muscle end potential is measured - No change in normal patients - Reduction by > 10-15 % in myasthenic patients. Single fiber electromyography Demonstrates blocking and jitter with normal fiber density Most sensitive diagnostic test for MG with sensitivity of greater than 95% Confirmatory but not specific Often performed in conjunction with repetitive nerve stimulation test (Oxford handbook)
Elevated ACH Receptor Antibodies (ACHR Antibodies)
Repetitive Nerve Stimulation test (RNS)
Positive Edrophonium test (Tensilon test)
Single Fiber Electromyography (SFEMG)