It is called "dermatomyositis sans myositis", basically dermatomyositis without the muscle disease symptoms.
Let us hope your disease stays at that stage, and from what I've read, in many people it does stay at that stage.
If you get muscle weakness, note down how it feels, is it the same on both sides of the body, what activities does it affect, which muscles? Take that info to your doctor.
http://emedicine.medscape.com/article/332783-overview
"Dermatomyositis-sine myositis, also known as amyopathic dermatomyositis (ADM), is characterized by typical cutaneous disease, no clinical evidence of muscle weakness, and normal serum muscle enzyme levels for at least 2 years.
"Patients who have undergone disease-modifying therapies such as corticosteroid or immunosuppressive agent treatment are not classified as having ADM.
"Some patients with ADM have abnormal findings on ultrasonography, MRI, or muscle biopsy. These patients have subclinical muscle involvement, but their condition may still be classified as ADM. Because many patients with ADM are not evaluated beyond clinical and enzymatic studies, many believe that ADM represents a systemic process that requires systemic therapies."