There is a higher incidence of other autoimmune conditions in myasthenia, notably thymoma and thyroid dysfunction. Tests to confirm the diagnosis include edrophonium challenge, repetitive nerve stimulation, single-fiber electromyography (EMG) of the frontalis, and assays for antibody directed against the acetylcholine receptor: all are less sensitive for ocular myasthenia than for generalized myasthenia. Dynamic abnormalities of myasthenic eye movements may reflect the primary hallmarks of the disease, which are fatigability and variability in strength, or secondary adaptive effects by the central nervous system. Clinically, ocular myasthenia can mimic any form of pupil-sparing ocular motility disorder. The predilection of myasthenia for the ocular muscles may be related to differences between limb and extraocular muscles in either physiological function or antigenicity. Ocular myasthenia gravis is a not uncommon autoimmune disorder causing diplopia, ptosis, and weakness of lid closure.
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