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Abstract
It was observed that some of the patients with acquired Myasthenia Gravis (MG), show symptoms and/or signs suggesting a possibility of central nervous system (CNS) involvement. It was investigated before over many years to look for indirect evidence of CNS involvement through neuropsychological tests, visual and brainstem evoked potentials, cerebrospinal fluid studies, and electroencephalographic changes. CNS involvement could be due to auto-antibodies against central acetylcholine receptors, vasculitic, demyelinating, or metastatic mechanisms. These effects can be due to the myasthenia itself, its association with other autoimmune diseases, or invasive thymic tumour with brain metastasis. Human leucocyte antigen (HLA) seems to be unique for Arabs and to have a role in judging the clinical situation for possible CNS involvement.
Our aim was to search for possible involvement of central nervous system in patients with acquired Myasthenia Gravis of various clinical types and to study the HLA type of our patients in correlation to CNS involvement.
We included thirty patients of various clinical types of acquired Myasthenia Gravis. Patients were seventeen males and thirteen females, their ages ranged from 17 to 82 years with a mean of 40.97 years and standard deviation of 15.65.
Patients were submitted to full history taking, full general and neurological examination and specially designed sheet, complete blood count, erythrocyte sedimentation rate, connective tissue screening, thyroid function tests, electromyographic studies, tensilon test, mediastinum computerized tomography, acetylcholine receptor antibodies (AChRAbs), visual and brainstem evoked potentials, cerebrospinal fluid studies, magnetic resonance imaging of the brain and human leukocyte antigen type screening.
Our results showed that CNS involvement was found in 6 (20%) patients with acquired myasthenia of various clinical types, the nature and aetiology remains unclear. Diabetes mellitus, hypertension and neurogenic manifestations were more frequent in those patients as well as acetylcholine receptor antibodies. The presence of thymic mass significantly correlated with MRI changes. Visual evoked potentials (VEPs) showed abnormally prolonged P100 in 43.3% and VEP wave form (amplitude) was abnormal in 26.7%. However these changes did not correlate with MRI brain changes. Neither brainstem evoked potentials (BAEPs) nor the cerebrospinal fluid (CSF) was an accurate tool to detect CNS changes. HLA type was found to be different from other groups of different ethnic background. Furthermore the type was different according to CNS involvement.
It is concluded that central nervous system involvement does occur in patients with acquired Myasthenia Gravis which can be suspected by the presence of diabetes millitus, hypertension, neurogenic manifestations, positive AChRAbs, and thymic mass. HLA type was specific to our patients as they have different ethnic background than the previously studied populations. Some differences were found in relation to CNS involvement.
It is recommended to exercise every effort to detect those myasthenic patients who are candidate for CNS involvement and submit them for further investigations and follow up to know more about the nature and pathology of the brain lesions. A bigger study should be designed with more strict criteria incuding younger patients, non diabetics and normotensives, thus minimising factors frequently associated with radiological brain changes. should be designed to study those central changes and HLA type.