Posttetanic potentiation in a patient with myasthenia gravis

We studied a patient with clinically typical myasthenia gravis (MG) and high serum titer of antibodies to acetylcholine receptor. Unlike the usual response in MG, there was an increment in the amplitude of the electrical response (308% of control) after 10 seconds of voluntary tetanus. Posttetanic facilitation is usually less than 200% in MG and over 200% in Eaton-Lambert syndrome. However, there have been several other cases of typical MG with increments over 200%. Facilitation of this magnitude has also been seen with curare administration in animals and man. However, in myasthenia, as opposed to curare poisoning, competitive blocking is not thought to exist.