**Core Concept**
IV immunoglobulin is a preparation of antibodies used to treat various autoimmune and immune-mediated conditions. It works by modulating the immune system's response, thereby reducing inflammation and suppressing abnormal antibody production.

**Why the Correct Answer is Right**
IV immunoglobulin is effective in treating conditions characterized by abnormal antibody production, such as autoimmune hemolytic anemia, thrombocytopenia, and autoimmune diseases like myasthenia gravis. In myasthenia gravis, IV immunoglobulin helps to reduce the production of autoantibodies against acetylcholine receptors, thereby improving muscle strength and reducing symptoms. The mechanism of action involves saturation of Fc receptors on immune cells, leading to a decrease in antibody-dependent cellular cytotoxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Myasthenia gravis is indeed a condition that can be treated with IV immunoglobulin, making this option correct and not a distractor. We will skip this option for the sake of explanation.

**Option B:** Idiopathic thrombocytopenic purpura (ITP) is a condition where IV immunoglobulin can be used as an emergency treatment to increase platelet count. However, the primary treatment for ITP is usually corticosteroids or splenectomy.

**Option C:** Hemolytic-uremic syndrome (HUS) is a condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. While IV immunoglobulin may be used in some cases, it is not the primary treatment for HUS.

**Option D:** Multiple myeloma is a type of plasma cell dyscrasia characterized by excessive production of monoclonal immunoglobulins. IV immunoglobulin is not used to treat multiple myeloma, as it may actually worsen the condition by increasing the production of abnormal antibodies.

**Clinical Pearl / High-Yield Fact**
IV immunoglobulin is most effective when administered as a short-term treatment, typically in the range of 1-2 weeks, to rapidly modulate the immune response.

**Correct Answer:** B. Idiopathic thrombocytopenic purpura