Is an abnormal rns with a >12% decrement (not done on an area that is really weak) specific for myasthenia gravis? please assume patient has signs and symptoms of generalized mg, as this is the case.

Maybe: An rns study is considered positive if the decrement is > 10% but a decremental response is not specific for myasthenia gravis. Decrements may be seen in other disorders of neuromuscular transmissions (lamber-eaton myasthenic syndrome, botulism) and motor neuron disease.

Not necessarily: Really require more than one area of decrement, and even so, nonspecific as can be seen with metabolic problems, muscle disease, neuropathies, and even can be artifactual. Maybe a tensilon test would be helpful, but of course, better approach via anti-neuromuscular junctional antibody or anti-musk results. In the end, if responding to mestinon, (pyridostigmine) may be a good confirmatory sign, also.