After I was diagnosed with CIDP (at age 42), I responded very well to IVIg. There was only one problem — I was tired all the time. After a while, I noticed that I was having a lot of gastro problems. It seemed like eating bland things would be a good idea, but the more I ate (bread, pasta, etc.), the sicker I got. Fortunately, I have a neighbor who was diagnosed with Celiac Disease and she helped me self-diagnose. Later, I found an article, co-authored by the neurologist that I see (Dr. Chin in NYC) that showed a high degree of correlation between CIDP and Celiac Disease (both are autoimmune in origin). One of the effects of Celiac is difficulty absorbing nutrients. This could lead to slow growth.
Just a thought.