The ocular signs and symptoms of myasthenia gravis

Abstract

Myasthenia gravis is a chronic disease characterized by a fluctuating weakness of voluntary muscles, with a preference for the muscles innervated by the cranial nerves. Ocular symptoms (ptosis, diplopia) were present at onset in 65% of 432 own patients and in 10% of these patients the disease remained confined to the extrinsic eye muscles. A complete remission occurred in 30% of the purely ocular cases within 10 years of onset. The diagnosis depends upon the pattern of weakness, the spontaneous or provoked fluctuation of the symptoms and the favourable response to anticholinesterases. The presence of antibodies against acetylcholine receptor protein is the most recent tool to confirm the diagnosis, but they are absent in 10–20% of the patients with generalized MG and in 20–50% of the purely ocular cases. As the reaction to anticholinesterases in ocular MG is sometimes equivocal or even absent auxillary investigations (electromyography, tonography, nystagmography, curaretest) may be necessary. Oral anticholinesterases (Pyridostigmin, Prostigmin, Ambenomium) usually have a moderate effect on the ptosis and a poor effect on the diplopia so that other measures (ptosishooks, covering one eye) are necessary. In selected patients alternate-day Prednisone is the therapy of choice.