The histomorphology of the thymus in late onset, non-thymoma myasthenia gravis

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