Thymic lymphoepitheliomas and skeletal muscle expressing common antigen(s)

From basic immunobiology to the upcoming WHO-classification of tumors of the thymus. The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors and related recent developments

The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors in Leiden, The Netherlands, 1998, set the stage for an interdisciplinary meeting of immunologists, pathologists and members of various clinical disciplines to exchange their recent findings in the field of thymus-related biology, pathology, and medicine. The contributions covered such diverse subjects as the role of transcription factors and cytokines in the development of the thymic microenvironment, thymic T, B and NK cell development, the pathogenesis of myasthenia gravis and other thymoma-associated autoimmunities, the pathology of thymic epithelial tumors and germ cell neoplasms, and new approaches to their diagnosis and treatment. This editorial will briefly sum up the data presented at the Conference and will comment on related novel findings that have been reported since then. Because it was also at the Leiden Conference, that the proposal of the WHO committee for the classification of thymic tumors was discussed for the first time, a description of the upcoming WHO Classification of Tumors of the Thymus is given with emphasis on the diagnostic criteria of thymic epithelial tumors, that should now be termed as type A, AB, B1-3 and type C thymomas, to make pathological and clinical studies comparable in the future.

Antibodies to skeletal muscle in myasthenia gravis. Part 3. Relation with clinical course and therapy

Fluctuations of anti skeletal muscle antibodies (AMA) were studied in relation to clinical changes and fluctuations in anti acetylcholine receptor antibodies (a-AChR). Forty-two patients with generalized myasthenia gravis were studied in clinical and serological follow-up during several years under various conditions. Results from this study demonstrate that AMA fluctuate in strong relation to a-AChR, clinical course and immunosuppressive therapy. Thymomectomy resulted in an increase or de novo appearance of AMA in 10 of the 12 patients who did not receive immunosuppressive medication.

Antibodies to skeletal muscle in myasthenia gravis. Part 2. Prevalence in non-thymoma patients

Anti-skeletal muscle antibodies (AMA) were measured in 340 non-thymoma patients with myasthenia gravis (MG) by both an ELISA with citric acid muscle extract and by immunofluorescence assay. Three a-AChR negative but AMA-positive patients were found. The occurrence of AMA was related to the age at onset in patients with an onset of MG beyond 40 years and with duration of disease in patients with an earlier onset of MG. This stresses the heterogeneity of late onset and early onset MG. Serial measurements in individual patients revealed no evidence for a thymic role in the generation of AMA. There was no difference in specificity of AMA in early and late onset patients. The presence of AMA in CT-negative patients is not necessarily suggestive of a radiological shortcoming in the detection of thymoma since in 16 AMA-positive patients from our series no thymoma was found at operation or obduction.

Myasthenia gravis with thymoma is not associated with an increased incidence of non-muscle autoimmune disorders

Three groups of thymectomized patients with myasthenia gravis (MG) were selected for study, 16 with thymoma, 16 with thymic atrophy and 32 with follicular hyperplasia of the thymus. All 16 patients with thymoma, 15/16 with thymus atrophy and 30/32 with follicular hyperplasia had AChR antibodies. Non-receptor muscle (CA) antibodies were found in sera of 15/16 patients with thymoma, 3/16 with thymus atrophy and in none of the sera from patients with follicular hyperplasia. There were 2 patients with thymoma and polymyositis, but none of the thymoma patients had rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) or other autoimmune disorders. Among the 32 patients with follicular hyperplasia of the thymus were 2 with SLE, 2 with RA and 1 with juvenile diabetes mellitus. In this study, there was an increased incidence of non-muscle autoimmune disorders among MG patients with follicular hyperplasia of the thymus but not among MG patients with thymoma.

CA-antibody: an immunological marker of thymic neoplasia in myasthenia gravis?

We have examined sera from 141 patients with myasthenia gravis and 11 non-myasthenia gravis patients with thymoma for antibodies to a citric acid extract of skeletal muscle (CA-antibodies). Sera were obtained from 5 different centers. The thymus histology was defined in each case. Sera from 56/66 patients (85%) with thymoma contained CA-antibodies, while such antibodies were only detected in 6/75 (8%) of the non-thymoma patients. None of the patients with thymus hyperplasia had CA-antibodies. One MG patient who developed MG after a bone-marrow transplantation, also developed CA-antibodies. The remaining 5 CA positive non-thymoma MG patients were all greater than 65 years and had thymic atrophy. Two of them had myasthenia gravis and polymyalgia rheumatica. In 2 thymoma patients with non-detectable levels of CA-antibodies before thymectomy, such antibodies were demonstrated in high titres after the operation. In 2 other sera from thymoma patients, the titres of CA-antibodies fell to less than 32 after thymectomy. There were 3 sera with CA-antibodies among 11 sera from non-MG patients with thymic tumours.