Mixed connective tissue disease includes all the following except:
**Core Concept**
Mixed connective tissue disease (MCTD) is a chronic autoimmune disorder characterized by overlapping features of systemic lupus erythematosus (SLE), scleroderma, and polymyositis/dermatomyositis. It involves the production of autoantibodies against multiple components of the cell nucleus and cytoplasm, leading to inflammation and tissue damage.
**Why the Correct Answer is Right**
MCTD typically presents with a combination of clinical features such as fever, arthritis, myositis, and skin manifestations, along with the presence of specific autoantibodies like anti-U1 RNP. The disease often follows a relapsing-remitting course, with patients experiencing periods of flare-up and remission. The presence of anti-U1 RNP antibodies is a hallmark of MCTD, distinguishing it from other autoimmune diseases.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because MCTD does not typically present with granulomatosis with polyangiitis (GPA), a condition characterized by granulomatous inflammation and vasculitis.
**Option B:** This option is incorrect because MCTD does not typically present with primary biliary cholangitis (PBC), a chronic autoimmune liver disease characterized by the destruction of bile ducts.
**Option C:** This option is incorrect because MCTD does not typically present with Sjögren's syndrome, an autoimmune disorder primarily affecting the exocrine glands, particularly the salivary and lacrimal glands.
**Clinical Pearl / High-Yield Fact**
MCTD is often associated with the presence of anti-U1 RNP antibodies, which can help differentiate it from other autoimmune diseases. Remember that MCTD is a diagnosis of exclusion, and patients should be thoroughly evaluated for other underlying conditions before making a diagnosis.
**Correct Answer:** D