Clinical and Laboratory Evaluation of the Autonomic Nervous System in Primary Sjogren's Syndrome

Sj(SqrRoot)(Delta)gren s syndrome (SjS) is a systemic exocrinopathy that affects as high as 5 percent of the population. It is manifested predominantly as dry eyes, dry mouth, and fatigue. The exocrinopathy can be encountered alone (primary SjS) in approximately one half of the patients or in the presence of another autoimmune disorder such as rheumatoid arthritis, systemic lupus erythematosus, or systemic sclerosis (secondary SjS). The most widely accepted classification for SjS is the American-European consensus classification criteria for SjS.(Vitali, Bombardieri et al. 2002)

Current understanding about the pathogenesis of SjS stems from the assumption that the autoimmune destruction of the exocrine glands leads to their hypofunction and symptoms of dryness. The existing evidence however does not fully support this assumption and cannot explain the underlying pathogenic mechanisms of SjS for the following reasons: 1) Discordance between severely affected function and abundance of histologically normal and ex vivo functional salivary glands; 2) at least 20% of patients have no evidence of systemic autoimmunity; 3) Animal models of SjS develop glandular dysfunction long before they develop autoimmunity; 4) Dryness and related symptoms respond poorly to immunosuppressive, including newer biologics, but fairly well to secretagogues such as pilocarpine. 5) No pathogenic antibodies or target epitopes have been identified to date to unify the pathogenesis of the syndrome.

All exocrine glands are innervated by the autonomic nervous system (ANS) and dysautonomia can mimic the phenotype of SjS, particularly cardinal manifestations, such as xerostomia and xerophthalmia. Thus we hypothesize that ANS dysfunction is central to the pathogenesis of SjS and propose to systematically study the ANS function in our cohort of patients with primary SjS compared with normative data from age and sex-matched controls. This protocol calls for a comprehensive evaluation of autonomic function, using physiological, neuropharmacologic, neurochemical, and imaging approaches, to identify consistent distinctive patterns of ANS involvement in SjS and thereby improve the diagnosis and understanding of pathophysiologic mechanisms of SjS.