Myasthenia gravis after etanercept and ustekinumab treatment for psoriatic arthritis: A case report.

A 35-year-old man was diagnosed with psoriatic arthritis treated with methotrexate and cyclosporine, the latter was then interrupted. Subsequently, etanercept was introduced, administered for 10 years and then replaced with ustekinumab. Six months after treatment with ustekinumab, patient underwent a chest CT scan for pneumonia, showing an anterior mediastinal mass which turned out to be a thymoma. He was referred to our department with fatigue, difficulty in raising arms and transient episodes of diplopia after exertion. Clinical history revealed that these symptoms had begun about 7 years previously but were ascribed to psoriatic arthritis. A diagnosis of anti-acetylcholine receptor antibodies positive myasthenia gravis was made; a higher dosage of methotrexate and prednisone were started with regression of symptoms. Our case increases the number of clinical reports of myasthenia gravis onset in patients with a history of rheumatic disease treated with anti-TNFα drugs. We speculate that ustekinumab could contribute to clinical worsening.