Patient with rheumatoid arthritis?

Autoimmune disease tend to be like STDs!: Where you find one, expect to find another one!!!

In this case, I believe that the second autoimmune disease is Sjögren's syndrome. Dysfunction of the salivary glands prevents the release of saliva into the buccal cavity and along with this follows disrupted release of secretory IgA, lysozyme and other components of non-specific defence. Subsequently, normal buccal flora (esp. viridans Streptococci) overproduces and the enamel is eroded, causing caries.

In a way, its the counterpart of bacterial vaginosis in the context of disruption of the vaginal pH, or candidiasis in the context of elevated vaginal pH (--> the view of a potential Ob-Gyn!!!) .

you re right.C is the correct answer.Here s an explanation from kaplan qbank:
. Rheumatoid arthritis can coexist with a variety of autoimmune diseases (including
those listed in the answers), but is most frequently associated with Sjögren's syndrome. Sjögren's syndrome is
due to autoimmune involvement with subsequent scarring of the salivary and lacrimal glands, leading to dry
eyes and dry mouth. Secondary effects include parotid gland enlargement, dental caries, and recurrent
tracheobronchitis *