THE HISTOMORPHOLOGY OF THE THYMUS IN LATE-ONSET, NON-THYMOMA MYASTHENIA-GRAVIS

Twenty-two late-onset, non-thymoma myasthenia gravis (MG) patients wer e selected for study based on the combined presence of MG and involuti on of the thymus. Thymectomy specimens from all the patients were exam ined histologically and immunohistologically and compared with an age- matched control group in which tissue was removed from the thymic glan d during operations for various cardiac conditions. We were not able t o find any morphological differences between thymi from MG patients an d patients in the control group. Germinal centres were present in 7/22 in the patient group and 6/20 in the control group. Seven of our 22 M G patients had auto-antibodies to titin. Germinal centres in the thymu s were found in only one. In contrast germinal centres were present in the thymus of 6/15 MG patients with no detectable antibody response t o titin (p = 0.01). Our study suggests that late-onset MG is pathogene tically heterogeneic with different modes of auto-sensitisation. Eur J Neurol 5:401-405 (C) 1998 Lippincott-Raven Publishers.