The fact that you have SLE lupus and have tested positive for the anti RNP antibody is a definite diagnosis of mctd. UCTD, in contrast is often used when there is an overlap but it is not clearly defined by symptoms and/or labs. MCTD is a specific diagnosis and classically includes sle lupus, scleroderma and polymyositis. Since this overlap disease was defined in 1972 some researchers have included other diseases into the mix: RA and dermatomyositis the main ones. That does not mean you will have symptoms of 3, 4 or 5 diseases.
Understanding overlap diseases is difficult. If lupus is the disease with a 1000 faces then mctd has 10000. You can present with one disease but never show symptoms of the others. Your disease can progress and present with symptoms of the other diseases or not. I have known many with mctd and each case was different in presentation and progression. Most were fairly mild, except mine. Treatment is similar to lupus: prednisone first line treatment, other immuno suppressants, biologics (ivig, rituxan) and other treatments.
My case presented as lupus but within a short time I had severe muscle weakness and fatigue. I was put on 60mg prednisone but the disease rapidly progressed and it took ivig to suppress the polymyositis symptoms. Lupus hit me hard: all joints, kidneys, entire GI tract, and cognitively. Scleroderma has not really been a problem unless you can blame it for raynauds phenomena which can also accompany lupus or pm without the overlap.
How are you currently being treated?
You have been dealing with lupus for over 2 years and dealing with mctd is not much different...you just have more things to consider. My experience is that most patients tend to develop symptoms of 1 or 2 of the possible diseases with one being the worst. In my case it was pm followed by lupus.
By the way, even though my case was extreme I have been in full remission since Jan 2006 and off all controlling meds for over a year.
MCTD (SLE Lupus, polymyositis, scleroderma). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, barretts esophagus, quadriplegic in 2005. Recovered and now active in downhill skiing, golf, hiking. Meds: amlodipine, benezapril, omeprazole, potassium, folic acid, vitamins, maxide.
Remain Optimistic and you can overcome.