Abstract
RATIONALE: Patients with myasthenia gravis may also have comorbid autoimmune diseases. Since both myasthenia gravis and neuromyelitis optica spectrum disease are mediated by antibodies, they are likely to occur together. However, since multiple sclerosis is an autoimmune disease that is not mediated by a specific antibody, it has fewer immune mechanisms in common with myasthenia gravis than neuromyelitis optica spectrum disease. We encountered a case of newly developed multiple sclerosis in a patient with myasthenia gravis. PATIENT CONCERNS: A 46-year-old man was diagnosed with ocular myasthenia gravis 6 years ago and had been taking pyridostigmine to control his symptoms. DIAGNOSIS: The patient developed right optic neuritis, and multiple sclerosis was suspected based on the brain magnetic resonance imaging findings. However, the required diagnostic criteria were not met. INTERVENTIONS: Disease-modifying therapy was not initiated, and clinical progression of the disease was monitored. OUTCOMES: One year after the onset of optic neuritis, the patient developed myelitis and was diagnosed with multiple sclerosis, prompting treatment with disease-modifying therapy. LESSONS: When optic neuritis occurs in patients with myasthenia gravis, careful evaluation is necessary while considering the possibility that it may be the first symptom of a demyelinating central nervous system disease. Therefore, it is important to conduct shorter-interval monitoring and symptom screening for patients with neurological autoimmune diseases, such as myasthenia gravis, even if multiple sclerosis is not initially suspected, to achieve early detection of multiple sclerosis.