The pathogenic process in MG can be condensed in three main phases (Fig. 3). In an initial phase, auto-antibodies bind antigenic epitopes located in the AChR subunits, and the number of receptors decreases as a result of receptor cross-linking and an alteration of the receptor turnover. Complement factors attach to the neuromuscular junction, but end-plate destruction does not occur in this phase. Amplitudes of MEPPs and EPPs may be significantly reduced, but because of the large safety factor of the neuromuscular junction, there is no failure of neuromuscular transmission and clinical symptoms are absent. In the following phase, complement-mediated end plate destruction and transient cellular infiltration of the neuromuscular junction take place. Amplitudes of MEPPs and EPPs become markedly reduced, and the EPP quantal content often decreases. At this stage, neuromuscular transmission failure develops, and symptoms of fatigability and weakness occur. This phase approximately corresponds to the acute phase of the EAMG in rats. In the final phase, cellular infiltration disappears and the structure of the end plate degenerates into a highly simplified pattern. MEPPs become extremely reduced in amplitude or undetectable by conventional microelectrode techniques. Mild ongoing denervation and reinnervation takes place. The EPP quantal content becomes quite variable; decreased at end plates reinnervated by small nerve endings or increased at distorted end plates reinnervated by elongated nerve terminals. This phase roughly corresponds to the chronic phase of EAMG.
|Original language||English (US)|
|Number of pages||19|
|State||Published - 1994|
ASJC Scopus subject areas
- Clinical Neurology