THU0411 Myasthenia gravis without thymic pathology and polymyositis: a rare association

Background Myasthenia gravis(MG) is an autoimmune disease frequently associated with antibodies against the acetyl-choline receptor. These antibodies contribute to the characteristic defects in neuromuscular transmission. Inflammatory myopathies, as polymyositis(PM), are immune-mediated neuromuscular diseases. PM and MG present both with muscle weakness and other similar features; electrophysiological and laboratory features of each of them are distinct. In Literature there are only few reports about PM and MG association Objectives To evaluate the prevalence of MG in patients with PM in our case series Methods We enrolled patients with PM/DM visited in our Centre in past 10 years;diagnoses of PM/DM were based on Bohan and Peter criteria. The follow-up was conducted until December 2017 Results We made 17 PM/DM diagnosis:14 F and only 3 M aged 41–85 years (mean 65 y). We found 6 patients (42,8%) with association of PM ad MG. They are all F, aged 51–78 years (mean 61 y) who developed inflammatory myositis confirmed by increasing of CK, EMG, autoantibodies pattern positivity and deltoid biopsy. Paraneoplastic, post-infectious or post-vaccinal syndromes was excluded. At the onset all presented progressive proximal muscle weakness and pain and asthenia. After initial treatment with oral corticosteroids (0.5–1 mg/kg/day methylprednisolone) a minimal response was observed only as improvement of asthenia and decreasing of CK levels. After one month of therapy 2 patients developed a bilateral palpebral ptosis, one disphagya and mild dyspnea, one a severe intestinal pseudo-obstruction,2 a mild dysarthria, ipovision and a worsening of muscular tone. Pyridostigmine test was positive in all patients;antiAChR antibodies levels were high. We started high doses corticosteroids (methylprednisolone 500–1000 mg/day for 5 days)and pyridostigmine (180–240 mg/day)with smart improvement. After this we introduced an immunosuppressant:azathioprine in 3 patients, mycophenolate mophetile in 4 patients. At the same time, because of the severity of the disease, monthly cycles of high doses IgV (20 g/kg in 5 days) were performed in 5 patients.A stable remission was achieved and maintained in all patients Conclusions This is one of the largest case series of patients with PM/DM-MG overlap. Our findings suggest that this association is not so rare and that patients affected by PM presenting palpebral ptosis, diplopia, gastrointestinal or oral symptoms, bulbar symptoms, weakness, asthenia, should be evaluated to exclude a concomitant MG, despite the absence of thymic pathology.A patient with PM-MG overlap should allow us for proper management of both conditions. This may include a more adequate therapy providing simultaneous association between immunosuppressant, pyridostigmine and, if necessary, a short time of high doses IgV therapy References [1] Santos E,et al. Inflammatory myopathy associated with myasthenia gravis with and without thymic pathology:Report of four cases and literature review. Autoimmun Rev2017Jun;16(6):644–649. [2] 2 Sanguesa Gomez C, et al. Dermatomyositis and myastenia gravis:An uncommon association with therapeutic implications. Reumatol Clin 2015 Jul-Aug;11(4):244–6. [3] Paik JJ, et al. The Co-Existence of Myasthenia Gravis in Patients with Myositis:A Case Series. Semin Arthritis Rheum. 2014 June;43(6):792–796. Disclosure of Interest None declared