Plant-thorn synovitis is an uncommon cause of arthritis and has not been reported in Asian countries. Zanthoxylum ailanthoides, an aromatic plant distributed in East Asia, is used as a spice in Taiwan. We reported a case of acute monoarthritis over the third metacarpo-phalangeal joint of the right hand after an injury by the thorn of the Zanthoxylum ailanthoides. A thorn foreign body of 2.7 mm in length was detected in the joint by high-resolution ultrasonography and led to a surgical synovectomy. The patient recovered completely after synovectomy. Plant-thorn synovitis is easily negligible. Early diagnosis is difficult and frequently delayed. The removal of thorn by synovectomy is the only curative treatment for plant-thorn synovitis. Compared to CT and MRI, ultrasonography is inexpensive, nonradioactive, repeatable, and easily accessible. It could detect foreign bodies that are smaller than 0.5 mm. High-resolution ultrasonography is a useful tool for detecting plant thorn and could promote early diagnosis.

Sjögren's syndrome (SS) is a common, systemic autoimmune disease with characteristic manifestation of xerophthalmia and xerostomia. 1,2 Prevalence rates for SS vary widely around the world, including 0.1%-3.3% prevalence in European countries and 0.16% prevalence in Taiwan. 3,4 Autoimmune-mediated inflammation of salivary and lacrimal glands results in focal lymphocytic adenitis and eventual destruction of glandular secretory function. 2 If left untreated, SS severely impairs quality of life. 5 To date, the causes for SS development are still