Myasthenia Gravis Mimicking Third Cranial Nerve Palsy: A Case Report.

Background: The most common pituitary adenoma presentation is a visual field defect and inappropriate pituitary hormone secretion. The compression of the optic chiasm causes visual impairment. Large pituitary adenomas can rarely cause diplopia and ptosis secondary to adenoma's lateral extension into the cavernous sinus. Myasthenia gravis is an autoimmune disorder involving neuromuscular junctions. It is characterised by skeletal muscle fatigability, commonly involving extraocular muscles, face and limbs. It is estimated that 75% of myasthenia gravis patients present with ptosis and diplopia. The association of myasthenia gravis with pituitary adenoma is very rare.

Case description: A 30-year-old lady presented with headache, diplopia and ptosis of the left eye for 2 months. She was diagnosed with acromegaly secondary to pituitary adenoma. Ptosis is a rare presenting feature in pituitary adenoma. Her case was discussed in a multidisciplinary meeting, and the consensus was that her ptosis is likely secondary to pituitary adenoma, which was involving the left cavernous sinus. She underwent transsphenoidal resection of pituitary macroadenoma. Three weeks post-surgery, she developed bilateral ptosis, dysarthria and dysphonia, which was diagnosed as myasthenia gravis.

Clinical implications: Ptosis is a rare manifestation of pituitary adenoma. Nonetheless, pituitary tumour patients presenting with ptosis should be evaluated for the neuromuscular disorder. A high index of suspicion is required for early diagnosis and prompt treatment of myasthenia gravis.