RESUMO
BACKGROUND: Myasthenia gravis (MG) and myotonic dystrophy type 2 (DM2) are rare disorders individually, and their coexistence in the same patient is very rare. We present a patient in which these two diseases coexisted. CASE REPORT: The patient complained of diplopia, fluctuating limb weakness, and difficulties in swallowing and speaking. A neurological examination revealed diplopia, facial, weakness of the neck and proximal limb muscles, dysphagia, dysphonia, and myotonia. The patient's mother had DM2 and her maternal grandfather had cataracts. MG was confirmed in our patient by positive results for neostigmine and a repetitive nerve stimulation test, and elevated serum anti-acetylcholine-receptor antibodies, while DM2 was confirmed by electromyography and genetic testing. The patient improved remarkably after treatment with anticholinesterases, corticosteroids, and azathioprine. CONCLUSIONS: This is the second reported case of the coexistence of DM2 and MG in the same patient. Since the symptoms of these two diseases overlap it is very important to keep in mind the possibility of their coexistence, so that MG is not overlooked in patients with a family history of myotonic dystrophy.