The thymus in seronegative myasthenia gravis patients

A Case Report on Pseudo-Internuclear Ophthalmoplegia: A Rare Manifestation of Myasthenia Gravis

A 41-year-old male with recently diagnosed diabetes mellitus type 2 presented with drooping of the left eyelid with double vision and was found to have an adduction deficit in the left eye and nystagmus in the abducting right eye during conjugated gaze: a left-sided internuclear ophthalmoplegia (INO). A medial longitudinal fasciculus (MLF) lesion was excluded exhaustively with brain imaging. The possibility of a pseudo-INO was considered. The autoantibody profile demonstrated positivity to acetylcholine receptor (AChR) antibody. Repetitive nerve stimulation (RNS) and electromyography (EMG) were unremarkable. An acetylcholinesterase inhibitor trial showed a significant improvement in the ocular symptoms. Hence, the diagnosis of ocular myasthenia was confirmed. There was no evidence of a thymic hyperplasia. Herein, we discuss pseudo-INO being an atypical presentation of myasthenia gravis (MG), emphasizing the importance of having a strong suspicion despite unremarkable test results.

Autoreactive T Cells from Patients with Myasthenia Gravis Are Characterized by Elevated IL-17, IFN-γ, and GM-CSF and Diminished IL-10 Production

Myasthenia gravis (MG) is a prototypical autoimmune disease that is among the few for which the target Ag and the pathogenic autoantibodies are clearly defined. The pathology of the disease is affected by autoantibodies directed toward the acetylcholine receptor (AChR). Mature, Ag-experienced B cells rely on the action of Th cells to produce these pathogenic Abs. The phenotype of the MG Ag-reactive T cell compartment is not well defined; thus, we sought to determine whether such cells exhibit both a proinflammatory and a pathogenic phenotype. A novel T cell library assay that affords multiparameter interrogation of rare Ag-reactive CD4(+) T cells was applied. Proliferation and cytokine production in response to both AChR and control Ags were measured from 3120 T cell libraries derived from 11 MG patients and paired healthy control subjects. The frequency of CCR6(+) memory T cells from MG patients proliferating in response to AChR-derived peptides was significantly higher than that of healthy control subjects. Production of both IFN-γ and IL-17, in response to AChR, was also restricted to the CCR6(+) memory T cell compartment in the MG cohort, indicating a proinflammatory phenotype. These T cells also included an elevated expression of GM-CSF and absence of IL-10 expression, indicating a proinflammatory and pathogenic phenotype. This component of the autoimmune response in MG is of particular importance when considering the durability of MG treatment strategies that eliminate B cells, because the autoreactive T cells could renew autoimmunity in the reconstituted B cell compartment with ensuing clinical manifestations.

Essential role for autophagy during invariant NKT cell development

Autophagy is an evolutionarily conserved cellular homeostatic pathway essential for development, immunity, and cell death. Although autophagy modulates MHC antigen presentation, it remains unclear whether autophagy defects impact on CD1d lipid loading and presentation to invariant natural killer T (iNKT) cells and on iNKT cell differentiation in the thymus. Furthermore, it remains unclear whether iNKT and conventional T cells have similar autophagy requirements for differentiation, survival, and/or activation. We report that, in mice with a conditional deletion of the essential autophagy gene Atg7 in the T-cell compartment (CD4 Cre-Atg7(-/-)), thymic iNKT cell development--unlike conventional T-cell development--is blocked at an early stage and mature iNKT cells are absent in peripheral lymphoid organs. The defect is not due to altered loading of intracellular iNKT cell agonists; rather, it is T-cell-intrinsic, resulting in enhanced susceptibility of iNKT cells to apoptosis. We show that autophagy increases during iNKT cell thymic differentiation and that it developmentally regulates mitochondrial content through mitophagy in the thymus of mice and humans. Autophagy defects result in the intracellular accumulation of mitochondrial superoxide species and subsequent apoptotic cell death. Although autophagy-deficient conventional T cells develop normally, they show impaired peripheral survival, particularly memory CD8(+) T cells. Because iNKT cells, unlike conventional T cells, differentiate into memory cells while in the thymus, our results highlight a unique autophagy-dependent metabolic regulation of adaptive and innate T cells, which is required for transition to a quiescent state after population expansion.

Ocular myasthenia gravis: response to long-term immunosuppressive treatment

OBJECTIVE

Ocular myasthenia gravis is a subtype of myasthenia gravis that causes relatively mild disability, but may convert into severe generalised muscle weakness. A universal management plan for ocular myasthenia gravis has not been established. This study was performed to determine the outcome of ocular myasthenia gravis with the currently available therapeutic options.

METHODS

Retrospective analysis of 78 patients with ocular myasthenia gravis with a mean disease duration of 8.3 (range 0.5-58.3) years.

RESULTS

In 54 patients (69%) symptoms and signs remained confined to the extraocular muscles during the observation period. The remaining 24 patients (31%) developed symptoms of generalised myasthenia gravis; 50% of them within two years, 75% within four years after onset. A somewhat reduced risk of generalisation was found in those with mild symptoms, normal repetitive nerve stimulation test, and low or absent antiacetylcholine receptor (AChR) antibodies at the time of diagnosis. Patients receiving immunosuppressive treatment (corticosteroids and/or azathioprine) rarely developed generalised myasthenia gravis (six of 50, 12%). Those without such treatment, usually due to uncertain diagnosis and late referral, converted into generalised myasthenia gravis significantly more often (18 of 28, 64%).

CONCLUSIONS

The prognosis of ocular myasthenia gravis is good. A conventional scheme with short-term corticosteroids and long-term azathioprine seems adequate to achieve remission in most patients. The proportion of patients developing generalised myasthenia gravis was smaller in this population compared with previously published groups (usually 50%-70%). Early immunosuppressive treatment is at least partially responsible for this finding. Thymectomy (performed here in 12 patients with an abnormal chest CT) also correlated with a good outcome, but had no apparent advantage over medical treatment alone.

Ocular myasthenia gravis. A critical review of clinical and pathophysiological aspects

Myasthenia gravis (MG) is probably the best studied autoimmune disease caused by autoantibodies against the acetylcholine receptor (AChR) at the neuromuscular junction, subsequently leading to abnormal fatigability and weakness of skeletal muscle. Extraocular muscle weakness with droopy eyelids and double vision is present in about 90% of MG patients, being the initial complaint in about 50%. In approximately 20% of the patients the disease will always be confined to the extraocular muscles. The single most important diagnostic test is the detection of serum antibodies against AChR which is positive in 90% of patients with generalized MG, but only in 65% with purely ocular MG. Electromyographic studies and the Tensilon test are of diagnostic value in clear-cut cases, but may be equivocal in purely ocular myasthenia, especially the latter not rarely producing false-positive results. Treatment response to corticosteroids and anti-cholinesterase agents is satisfactory in many patients with ocular MG, however other immunosuppressive drugs may also be needed. Pathogenetically relevant steps of the underlying autoimmune process have been elucidated during the last few years; nevertheless a number of questions remain open, especially what starts off the autoimmune process, and why are eye muscles so frequently involved in MG?