Ocular pseudomyasthenia or ocular myasthenia 'plus': a warning to clinicians.

Myasthenia gravis (MG) commonly presents with weakness and fatigability of the lids and extraocular muscles, which respond to treatment with anticholinesterase medication. However, certain intracranial mass lesions may mimic these features of MG; alternatively, MG may mask the signs of a coexistent intracranial mass. We describe 8 patients originally diagnosed as having MG by knowledgeable clinicians, in whom an intracranial lesion instead of, or in addition to, MG was later identified. The lesions included parasellar tumors and aneurysms. In patients presenting with clinical features of ocular MG, it is therefore essential to establish a definite diagnosis of MG, to exclude other possible causes of "pseudomyasthenia," and to exclude other diseases that might be masked by coexisting myasthenic weakness. We recommend that patients with clinical features of MG limited to the ocular or cranial musculature be thoroughly evaluated for intracranial mass lesions, using CT or MRI if warranted.