[Clinical and electrophysiological peculiarities of seronegative myasthenia].

Thirty-seven patients with myasthenia gravis (MG) underwent AChR-Ab analysis, clinical study and neurophysiological examination - repetitive nerve stimulation (RNS). About 16,2% of MG patients who were anti-AChR-negative constituted a so-called seronegative MG group (SNMG). Compared to the AChR-Ab positive patients (SPMG), the SNMG was characterized by the higher female/male ratio (6:1), higher frequency of infantile onset of MG (33,3%), absence of association with thymoma and highest frequency of myasthenic crisis (83,3%). The clinical pattern of SNMG differed from SPMG and was characterized by predominant affect of mimic bulbar and respiratory muscles that determined severity of the course and high frequency of myasthenic crises. The identical clinical pattern was found in 19,3% of SPMG patients. However the character of neuromuscular transmission in orbicularis oculi muscle was different in SNMG and this SPMG-group. The pathological decrement was observed in 83,3% muscles of the SPMG-group (from -20% to -74%) and only in one case in the SNMG-group (-48%). Besides, the absence of clinical and neurophysiological responses to anticholinesterase was noted in the SNMG-group. Cholinergic neuromuscular hyperactivity in SNMG patients manifested itself in clinical fasciculations and myokymic contractions of muscles which prevailed in facial muscles in 66,7% of SNMG patients. Neurophysiologic examination displayed extra repetitive discharges after the compound motor action potential (R-CMAP) at low-frequency stimulation after acetylcholine esterase inhibitors in 100% cases.

[Myasthenic myopathy].

We have tested clinical and electrophysiological parameters as well as sera for specific anti-titin-antibodies in 40 myasthenic patients with thymoma, 10 with late-onset and 40 with early-onset without thymoma. We have revealed the prevalence of clinical symptoms: chew and bulbar disturbances, neck and deltoideus muscle weakness in the patients with thymoma and late-onset myasthenia gravis without thymoma. These clinical peculiarities were associated with the absence of changes in duration of minimal motor unit potential after correction for synaptic lesions by proserine injections and increase of titin-antibodies level. The clinical data, along with the results of electrophysiological and immunological studies, suggest a presence of "myasthenic myopathy" in patients with myasthenia, comorbid with thymoma, and patients with late-onset of myasthenia without thymoma.