Myasthénies oculaires : diagnostic et traitement

Myasthenia gravis is a rare, auto-immune disorder of the neuromuscular junction. Onset signs frequently involve ocular muscles, accounting for ptosis and/or diplopia in more than 75% of cases. Among the cases with purely ocular muscle involvement, less than one half will never progress towards a more general form of myasthenia. However, even if they do not share the potentially life-threatening course of generalized myasthenia, purely ocular forms are often responsible for severe impairment in everyday life. The diagnosis is essentially based on fluctuations in the time and topography of the ocular muscle weakness. It still remains uneasy, as investigations such as electromyography, search for antiacetycholine receptor antibodies (positive in 50% of cases of purely ocular myasthenia), and edrophonium chloride test sometimes yield false negative results. Whereas some patients get better while on anticholinesterasic drugs alone, most of them will experience insufficient improvement and need steroids and/or immunosuppressant drugs. There is no indication for plasma exchanges, intravenous immunoglobulin or thymectomy (except in the presence of thymoma). This treatment could well decrease the risk of an evolution towards generalized myasthenia. The reasons underlying the vulnerability of ocular motor muscles in myasthenia are complex and several factors (linked to immunology, anatomy and function) may combine to bring about their specific involvement. In the future, randomized, controlled trials will be necessary, in order to determine a more rational approach of the treatment of ocular myasthenia, which currently lies mostly on retrospective data and the expertise of reference centers implicated in the management of the disease.