A patient has been diagnosed with systemic sclerosis. He has the presence of anti RNA polymerase III antibody. Which of the following is more common in this patient?
**Core Concept**
Systemic sclerosis, also known as scleroderma, is a chronic autoimmune disease characterized by fibrosis and vascular alterations in the skin and internal organs. The presence of specific autoantibodies is a key diagnostic criterion. Anti-RNA polymerase III (anti-RNAP III) antibodies are associated with a more severe form of systemic sclerosis, particularly with diffuse cutaneous systemic sclerosis.
**Why the Correct Answer is Right**
Anti-RNAP III antibodies are directed against the enzyme responsible for RNA transcription in the mitochondria. This autoantibody is more commonly found in patients with diffuse cutaneous systemic sclerosis, which is characterized by rapid progression of skin thickening and involvement of internal organs. The presence of anti-RNAP III antibodies is associated with a higher risk of renal crisis, a life-threatening complication of systemic sclerosis.
**Why Each Wrong Option is Incorrect**
**Option A:** While anti-Scl-70 (anti-topoisomerase I) antibodies are also found in systemic sclerosis, they are more commonly associated with limited cutaneous systemic sclerosis, not diffuse cutaneous systemic sclerosis.
**Option B:** Anti-U1 RNP antibodies are primarily seen in mixed connective tissue disease, a distinct autoimmune disorder that overlaps with systemic sclerosis but has a different clinical presentation.
**Option C:** Anti-centromere antibodies are found in limited cutaneous systemic sclerosis and are associated with a more indolent course of the disease.
**Option D:** Anti-PM-Scl antibodies are associated with polymyositis and dermatomyositis, two autoimmune disorders that affect the muscles and skin but are distinct from systemic sclerosis.
**Clinical Pearl / High-Yield Fact**
In patients with systemic sclerosis, the presence of anti-RNAP III antibodies should prompt a thorough evaluation for renal involvement, including measurement of serum creatinine and urinalysis, to identify those at risk of renal crisis.
**Correct Answer: C. Limited cutaneous systemic sclerosis.**