Hi @linda59,
Welcome to Connect. I see that you posted in several places looking for information and answers, and how to categorize GCM (Giant Cell Myocarditis). Let's focus your questions to the Heart and Blood Health group.

GCM is a rare cardiovascular disorder (heart disease). Here is more information from National Organization of Rare Diseases http://rarediseases.org/rare-diseases/giant-cell-myocarditis/

As the article states "Giant cells are abnormal masses produced by the fusion of inflammatory cells called macrophages." Also, the causes of GCM are unknown. About 20% of cases happen in people with autoimmune disorders. So the system's autoimmune system may play a role in the development of the disease.

In the same article, you'll see that Mayo Clinic researchers are studying the use of immunosuppressive drugs combined with steroids to treat individuals with giant cell myocarditis. Contact information is also provided.

I'm also tagging @smiley2929 who may be able to share her experiences of myocarditis with you.