Paraneoplastic myasthenia gravis: immunological and clinical aspects.

ABSTRACT

Paraneoplastic myasthenia gravis (MG) is accompanied by a neoplasm, usually thymoma. In patients with thymoma and a specific genetic make-up, the paraneoplastic immune response develops further in thymic remnant or peripheral lymphatic tissue. Paraneoplastic MG and late-onset MG (age >or= 50 years) share a similar immunological profile with high titin and ryanodine receptor (RyR) antibody prevalence. This profile is the most important predictor of clinical outcome in paraneoplastic MG. The presence of a thymoma per se does not cause more severe MG. MG severity is linked to the patient's immunological profile. Paraneoplastic MG causes a distinctive non-limb symptom profile at MG onset, characterized by bulbar, ocular, neck, and respiratory symptoms. When the diagnosis of paraneoplastic MG is established, the neoplasm should be removed surgically. Pre-thymectomy plasmapheresis or iv-IgG should be considered in these patients to minimize post-thymectomy MG exacerbation risk. Paraneoplastic MG usually continues after thymectomy. The pharmacological treatment of paraneoplastic MG does not differ from non-paraneoplastic MG, except for tacrolimus that should be considered in difficult cases. Tacrolimus is an immunosuppressant acting specifically in RyR antibody positive patients through enhancing RyR-related sarcoplasmic calcium release that in theory might be blocked by RyR antibodies, causing symptomatic relief in paraneoplastic MG.