This is a double blind, randomized, placebo controlled, trial involving 60 patients, half of which will receive IVIg and the other half placebo (D5/W). Because IVIg is prohibitively expensive, a controlled trial is needed to provide convincing evidence of efficacy, and ensure that the benefit is not due to spontaneous improvement or to observer bias. The dose of IVIg is 2 GM/Kg divided into two daily doses administered monthly for six months. The drug will be considered effective if patients experience an increase of more than 25% in their baseline muscle strength. Muscle strength will be assessed with a series of objective dynamometric measurements performed before and after each monthly infusion.