I have autoimmune disorder even though my ANA and all other immunological blood tests are negative. Have been tested for Sjogren many times it was always negative, and my lip biopsy (about 15 years ago) showed mild inflammation nonspecific to Sjogren. During these years I had a few positive borderline results which became negative when repeated a few years later.
But there is no doubt that my POTS, fatigue and probably the sensory symptoms of my SFN, are responding greatly to Rituximab and prednison.

If you had some positive RA and Sjogren blood tests in the past isn't it enough to justify a diagnosis and immunological treatment ?
In my case I got the Rituximab based on the progression of my symptoms, my response to treatments and some autoimmune disorders in my family.