Immunoglobulin is a blood product derived from large pools of donated human plasma that contains the part of the blood that contains antibodies. It is usually given intravenously (IVIg), but it can be given subcutaneously (SCIg) (under the skin). Doses are based on the patient’s weight, initially with a dose of 2g/kg given over 2-5 days, then 1g/kg/month for several months, then tapered depending on the response.
Because IVIg is very expensive and requires intravenous administration, it is usually reserved for cases that are resistant to other treatments. However, it is often especially effective for patients with refractory dermatomyositis skin symptoms and patients with interstitial lung disease. Some physicians also use IVIg alone as first-line therapy in patients who have necrotizing myopathy with the anti-HMGCR autoantibody.
Some physicians use IVIg to treat inclusion body myositis, although the effectiveness of this is questionable. Nevertheless, some patients who have dysphagia (swallowing problems) do seem to benefit.
Side effects of immunoglobulin therapy are rare and may include flu-like symptoms: backache, headache, fever, chills, general discomfort, and joint pain. Side effects can be related to the rate of infusion, and slowing this rate often relieves unwanted effects. Premedication with Benadryl or Tylenol can also prevent some of these side effects.
On rare occasions, a patient may have an infusion reaction, which can cause symptoms of hives, shortness of breath, and even anaphylaxis (a life-threatening allergic reaction). Before IVIg is started, the patient should be tested to see if they have IgA in their blood. Up to 5% of the general population has an IgA deficiency, and if you have it and you receive a preparation with IgA antibodies, then a reaction may occur. If IgA deficiency is detected, then IVIg preparations that do not have IgA in them can be administered. Sometimes IV steroids are also given to reduce the incidence of infusion reactions.
IVIg is very expensive and typically requires repeated doses.