The Coexistence of Myasthenia Gravis and Myotonic Dystrophy Type 2 in a Single Patient
A 30-year-old woman first noticed double vision 2 years prior to hospitalization. It had been present periodically, mostly in the evenings, and did not disturb the patient sufficiently to seek medical attention. Three months later she noticed leg weakness with walking difficulties, especially when climbing and walking down stairs, and walking instability resulting in consecutive falls. Six months later weakness of the arms appeared that caused difficulties in washing and combing her hair. After seven months she noticed difficulties in swallowing and nasal speech after prolonged talking. All of these symptoms had a fluctuating course and were more pronounced in the evenings.\nA neurological examination revealed diplopia due to the weakness and fatiguability of the rectus superior and rectus lateralis muscles of the left eye as well as of the rectus inferior of the right eye, moderate weakness of the facial muscles, mild dysphagia with nasal speech, mild weakness of neck muscles, and weakness and fatiguability of proximal limb muscles. Very mild active and percussion myotonia were observed, but the patients had not been aware of it prior to hospitalization. The patient's mother had been diagnosed with DM2 at the age of 48 years and her maternal grandfather had cataracts.\nA diagnosis of MG was confirmed in our patient by clear positive results in the neostigmine test and decremental responses in the repetitive nerve stimulation test (RNST) (); these were 43% and 26% in the deltoid and nasal muscles, respectively. Anti-acetylcholine receptor (AChR) antibody titer was elevated (8.8 nmol/L, normal <0.2 nmol/L). A chest CT scan showed a persistent thymic tissue in the upper anterior mediastinum, and a pathohistological examination of the thymus after thymectomy revealed thymic hyperplasia. Electromyography during relaxation demonstrated diffuse episodes of myotonic discharges () in multiple muscles, while during voluntary muscle activity a mild myopathic lesion was revealed by short-duration motor-unit action potentials and early recruitment (). Genetic testing confirmed the presence of DM2. The patient improved remarkably after treatment with anticholinesterases, corticosteroids, and azathioprine.