You can be seronegative and still have Sjogren's Disease. I was diagnosed based on a lip biopsy, plus symptoms. Sjogren's is systemic, and usually impacts multiple systems (e.g. lungs, heart, digestive, etc.).
Inflammation from Sjogren's led to rapid development of cataracts in my case - going from "probably never need cataract surgery" to "need it within the next six months or so" from one year to the following.