• Grip strength in the more affected hand (primary endpoint) [ Time Frame: End of blinded cross-over period ] [ Designated as safety issue: No ]
• Upper limb subsection of the Guy's Neurologic Disability Scale (co primary endpoint) [ Time Frame: End of blinded cross-over period ] [ Designated as safety issue: No ]

The purpose of the study is to evaluate the efficacy (effect on grip strength and disability) and safety/tolerability of IGIV, 10% in subjects with Multifocal Motor Neuropathy.

• Drug: Immune Globulin Intravenous, 10%
• Drug: Immune Globulin Intravenous, 10% or Placebo (0.25% human albumin solution)

• Experimental: Stabilization Phases 1, 2, 3 (with Cross-Over Period 1 between Stabilization Phases 1 and 2 and Cross-Over Period 2 between Stabilization Phases 2 and 3): open label - all patients - Immune Globulin Intravenous, 10% at the same dose and frequency as prior to entering the study - length: 12 weeks
• Experimental: Cross-Over Periods 1, 2: randomized - double-blinded - length: maximum of 12 weeks with ability to move to next stabilization phase early if deterioration occurs

Inclusion Criteria:

• Written informed consent obtained from the subject prior to any study-related procedures and study product administration
• Diagnosis of definite or probable MMN based on the criteria of the American Association of Electrodiagnostic Medicine (AAEM). Diagnosis can be based on chart records. a) Hand grip (finger flexor) weakness of MRC grade 4 or less at onset or appearing prior to screening; b) Documented electrophysiological evidence of at least one site with conduction block with definite (50%) or probable (30%) reduction in area-under-the-curve (AUC) of the compound muscle action potential; c) No upper motor signs; d) No bulbar or cranial signs or symptoms; e) No clinically identifiable sensory abnormalities.
• Must be on a stable regimen of IGIV for at least 3 months prior to enrollment
• Treatment interval with IGIV of 2 to 5 weeks (+/- 3 days)
• Dose of IGIV to be 0.5 to 2.0 grams per kilogram bodyweight and infusion cycle
• Subjects are adults, male or female, at least 18 years of age
• If female and capable of bearing children - have a negative urine pregnancy test result at enrollment and agree to employ adequate birth control measures for the duration of the study
• Ability and willingness to travel to the study site for infusions and assessments if required by the protocol

Exclusion Criteria:

• Any disease that may cause neuropathy or may interfere with outcome assessments, such as diabetes requiring medication for control or vasculitis, including systemic lupus erythematosis
• Treatment with other immunosuppressive agents besides IGIV during the 3 months prior to enrollment (or treatment with Rituximab during the 12 months prior to enrollment)
• Cerebrospinal fluid protein > 100 mg/dL (if done as part of a previous evaluation)
• Subjects positive at enrollment for one or more of the following: Hepatitis B surface antigen (HBsAg), PCR for HCV, PCR for HIV Type 1
• Subjects with levels of alanine aminotransferase (ALT) or aspartate aminotransferase (AST) > 2.5 times the upper limit of normal for the testing laboratory
• Subjects with neutropenia (defined as an absolute neutrophil count [ANC] <= 1000/mm3)
• Subjects with serum creatinine levels greater than 1.5 times the upper limit of normal for age and gender
• Subjects with malignancy other than adequately treated basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix
• Subjects with a history of thrombotic episodes (deep vein thrombosis, myocardial infarction, cerebrovascular accident)
• Subjects who received any blood or blood product exposure other than an IGIV, subcutaneous immunoglobulin, immune serum globulin (ISG) preparation, or albumin within the 6 months prior to enrollment
• Subjects with an ongoing history of hypersensitivity or persistent reactions (urticaria, breathing difficulty, severe hypotension, or anaphylaxis) following IGIV
• Subjects with immunoglobulin A (IgA) deficiency and known anti IgA antibodies
• Subjects using another investigational product or device within 30 days prior to enrollment
• Subjects who are unable or unwilling to meet all the requirements of this study
• If female, is pregnant or lactating at time of enrollment