Intravenous Immunoglobulin and Plasma Exchange in Myasthenia Gravis

Inclusion Criteria: * \>18 years old * diagnosis of moderate-severe MG (defined as a Quantitative Myasthenia Gravis Score QMGS \>10.5) * worsening weakness requiring a change in therapy judged by a neuromuscular expert Exclusion Criteria: * Worsening weakness secondary to concurrent medications (e.g. Aminoglycosides) * Worsening weakness secondary to infection * Change in corticosteroid dosage in the 2 weeks prior to screening * Other disorders causing weakness or fatigue * Known absolute IgA deficiency (risk of anaphylactic reaction to IVIG) * History of anaphylaxis or severe systemic response to IVIG or albumin * Pregnancy or breastfeeding * Active renal failure precluding volume of IVIG (risk of volume overload with IVIG) as judged by the investigators * Clinically significant cardiac disease precluding IVIG volume as judged by the investigators * Known hyperviscosity or hypercoaguable state (risk of stroke with IVIG) * Known coagulopathy with bleeding * On another current study medication or protocol within 4 weeks of screening * Patients with known refractory status to either IVIG or PLEX * Poorly controlled or severe hypertension (exacerbation by IVIG) * Patient refuses treatment with either IVIG or PLEX * Patient refuses follow-up with electrophysiological studies * Patient unable or unwilling to give informed consent