LATE-ONSET MYASTHENIA-GRAVIS

Late onset myasthenia gravis (MG) is defined as the onset of the disea se after the age of 50 in a patient with no clinical or paraclinical e vidence of a thymoma, Myasthenia gravis has a bimodal appearance for b oth sexes with a peak age of onset located in the early onset group an d another peak for late onset of MG, Early onset of MG in men is appro ximately 10 years later than in females. In late onset MG, the thymus is smaller than in early onset and much of the lymphoid tissue has bee n substituted with fat. There is no morphological evidence that the th ymus atrophy seen in late onset MG is any different from the thymus in volution which is age-related, The AChR antibody concentration is lowe r in cases with late onset MG than it is in early onset and in thymoma -associated MG. Sera from late onset MG patients can be divided in 2 g roups; those with and those without striated muscle (MGT 30) antibodie s. Their presence is not an effect of age since they are not detected among old healthy individuals, Nor is it an effect of long MG duration , since there is no relation between titre and duration. Non-thymoma M G patients who demonstrate an immune response to titin identical to th at observed in thymoma, have a worse prognosis and seem to do less wel l after thymectomy than late onset MG patients without muscle antiboid es.