[Ultrastructure of the neuromuscular junction in myasthenia]

The ultrastructure of neuromuscular synapses were investigated in bioptic specimens of muscles in 15 patients with myasthenia. Changes were detected in the pre- and postsynaptic structures. As a rule, the process initiates with appearance of destructive changes in the terminals of axones and in the adjacent to them areas of the "sole" of the neuromuscular junction, which may lead to destruction of synaptic contacts. In some part of synapses, together with destructive changes, there were observed also regenerative changes. The most representative group of synapses were those possessing the following characteristics of the ultrastructure: an increased electron density of the axoplasm and a greater number of mitochondria in the terminals of the axones; changes in the organization of the symaptic cleft and folds; impoverishment of the "sole" in organellas; all these signs, according to the literature reports, should be considered as typical of myasthenic lesions of the neuromuscular synapses. Collation of the changes observed with the duration periods of the disease, as well as the fact that these changes can be seen in the same patients, justify the assumption about the existence of different stages of the synaptic defect: destructive, destructive-regenerative and myasthenic. From this point of view, the appearance of "myasthenic" synapses may be considered as a result of the proceding destructive-regenerative process.