A patient presenting with Raynaud phenomenon, myalgias, arthralgias, and difficulty in swallowing is likely to have which antibody?

The presence of Raynaud phenomenon, myalgias, arthralgias, and difficulty in swallowing in a patient is highly indicative of an autoimmune condition, particularly mixed connective tissue disease (MCTD). The hallmark of MCTD is the presence of high levels of ribonucleoprotein (RNP) antibodies. These antibodies are specific for this condition and play a crucial role in its diagnosis.

RNP antibodies can be associated with symptoms such as those noted in the question, including muscle and joint pain and esophageal dysmotility, contributing to swallowing difficulties. Raynaud phenomenon, characterized by episodic vasospasm of the fingers and toes leading to color changes, is also commonly observed in patients with this and related connective tissue disorders.

The other antibodies listed are associated with different conditions. Anti-dsDNA antibodies are primarily linked to systemic lupus erythematosus, while anti-Smith antibodies are also specific for lupus. Cardiolipin antibodies are usually associated with antiphospholipid syndrome. Thus, the combination of symptoms and the presence of high level ribonucleoprotein (RNP) antibodies strongly supports the diagnosis of mixed connective tissue disease.