Myositis and myasthenia gravis (MG) are both autoimmune disorders presenting with muscle weakness. Rarely, they occur simultaneously in the same patient. Since the management of myasthenia gravis differs from that of myositis, it is important to recognize when patients have both diseases. We reviewed the cases of 6 patients with both myositis and MG to identify clinical features that suggest the possibility of co-existing MG in myositis patients.
We identified 6 patients with dermatomyositis or polymyositis and MG. We reviewed their medical records to assess their clinical presentations, laboratory findings, and electrophysiological features.
All 6 patients had definite dermatomyositis or polymyositis by the criteria of Bohan and Peter as well as electrophysiologic and/or serologic confirmation of MG. Among overlap patients, 5/6 (83%) had bulbar weakness, 2/6 (33%) had ptosis, and 1/6 (17%) had diplopia. Fatigable weakness was noted by 5/6 (83%) patients. Treatment with pyridostigmine improved symptoms in 5/6 (83%) patients. High-dose steroids were associated with worsening weakness in 2/6 (33%) patients.
Prominent bulbar symptoms, ptosis, diplopia, and fatigable weakness should suggest the possibility of MG in patients with myositis. A suspicion of MG may be confirmed through appropriate electrophysiologic and laboratory testing. In those with myositis-MG overlap, high-dose steroids may exacerbate symptoms and pyridostigmine may play an important therapeutic role.