Antibodies to skeletal muscle in myasthenia gravis. Part 1. Diagnostic value for the detection of thymoma

The anti-acetylcholine receptor antibody test in suspected ocular myasthenia gravis

Aim. To estimate the clinical significance of anti-acetylcholine receptor antibody (anti-AChR-Ab) levels in suspected ocular myasthenia gravis. Methods. In total, 144 patients complaining of fluctuating diplopia and ptosis were evaluated for serum levels of anti-acetylcholine receptor antibody and their medical charts were retrospectively reviewed. Subjects were classified into three groups: variable diplopia only, ptosis only, and both variable diplopia and ptosis. We investigated serum anti-AChR-Ab titer levels and performed thyroid autoantibody tests. Results. Patients' chief complaints were diplopia (N = 103), ptosis (N = 12), and their concurrence (N = 29). Abnormal anti-AChR-Ab was observed in 21 of 144 patients (14.1%). Between the three groups, mean age, number of seropositive patients, and mean anti-AChR-Ab level were not significantly different (P = 0.224, 0.073, and 0.062, resp.). Overall, 27.5% of patients had abnormal thyroid autoantibodies. Conclusion. The sensitivity of anti-AChR-Ab was 14.1% in suspected ocular myasthenia gravis and seropositivity in myasthenia gravis patients showed a high correlation with the presence of thyroid autoantibodies.

Correlation between acetylcholine receptor antibody levels and thymic pathology in myasthenia gravis: a review

Myasthenia gravis is the most common chronic autoimmune neuromuscular disease. Anti-acetylcholine receptor (AChR) antibodies are found in at least 80% of patients with generalized myasthenia and have been implicated in disease pathogenesis. Thymic abnormalities are frequently found in seropositive patients, and the thymus is thought to be involved in generation of autoimmunity. This article reviews existing literature on the role of AChR antibodies in the pathogenesis of myasthenia gravis, and the correlation between AChR antibody titers and thymic pathology. Most studies found that highest titers are seen in thymic hyperplasia, followed by intermediate titers in thymoma, and lowest titers in atrophic or normal thymus. One publication found no difference between titers in thymoma and normal thymus.

Eye muscle antibodies in patients with ocular myasthenia gravis: possible mechanism for eye muscle inflammation in acetylcholine-receptor antibody-negative patients

Myasthenia gravis is an organ-specific autoimmune disorder generally thought to be caused by an antibody-mediated attack against the skeletal muscle nicotinic acetylcholine (Ach) receptor (AchR) at the neuromuscular junction. Extraocular muscle weakness and double vision are present in about 90% of patients with myasthenia gravis and are the predominant complaints in about 20% of patients, when the condition is called ocular myasthenia gravis (OMG). While serum antibodies against the AchR are detected in most patients with generalized myasthenia gravis (GMG), they are not found in about one-third of patients with the ocular variety, and epidemiological, clinical, and serological studies suggest that OMG and GMG are two separate diseases. Both forms of myasthenia gravis are sometimes associated with thyroid autoimmunity or thyroid-associated ophthalmopathy (TAO). We have therefore tested the sera of patients with GMG and OMG by Western blotting for antibodies against porcine eye muscle membrane proteins in general, and by enzyme-linked immunosorbent assays (ELISA) specifically for reaction with two skeletal muscle antigens which are prominent marker antigens for TAO, namely, the calcium-binding protein calsequestrin and the so-called "64-kDa protein." The 64-kDa protein has recently been identified as the flavoprotein subunit of mitochondrial succinate dehydrogenase. Patients with ophthalmopathy and myasthenia were excluded. Nine of the patients had associated Graves' hyperthyroidism without evident ophthalmopathy and one had Hashimoto's thyroiditis. Antibodies against porcine eye muscle membrane antigens of M(r) 15-110 kDa were detected in patients with GMG or OMG, one or more antibodies being detected in 100% of patients with GMG and in 88% of those with OMG. The most frequently found antibodies were those targeting eye muscle membrane proteins of 15, 67, and 110 kDa. Antibodies reactive with purified calsequestrin (63 kDa) were detected in 21% of patients with OMG but in no patient with GMG. Antibodies recognizing purified succinate dehydrogenase (67 kDa) were found in 42% of patients with OMG, in 100% (5 of 5) of patients with GMG, and in 48% of all patients with myasthenia gravis not associated with Graves' hyperthyroidism. There was no close correlation between any eye muscle-reactive antibody and antibodies against the AchR in either group of myasthenic patients. The findings support the notion that immunoreactivity against skeletal muscle proteins other than the AchR may play a role in the development of the muscle weakness in AchR antibody-negative patients with OMG and GMG, although it is unlikely that any of the antibodies demonstrated in this study are directly implicated. Similarly, while the demonstration of antibodies reactive with eye muscle antigens associated with TAO in patients with OMG raises the possibility that the link between the ocular lesions of myasthenia gravis and Graves' disease may be autoimmunity against a common antigen(s), it is more likely that both disorders are mediated by cytotoxic T cells recognizing another cell membrane antigen, such as the novel thyroid and eye muscle shared protein G2s, and that serum antibodies reactive with succinate dehydrogenase Fp subunit and calsequestrin are markers of an immune-mediated eye muscle reaction.

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.