Abberant Sudomotor Functions in Sjögren's Syndrome: Comparable Study with Atopic Dermatitis on Dry Skin Manifestation

This chapter summarizes recent advances in the pathogenesis and management of Sjögren's syndrome (SS). Major topics are newly described pathomechanisms and cutaneous manifestations of SS, with special references to hypohidrosis and related mucocutaneous manifestations. Although the significance of cutaneous manifestations in SS has been gradually recognized in rheumatologists, sudomotor function has not been fully evaluated and recognized in the diagnosis of SS except by dermatologists. SS is a relatively underestimated collagen disease in contrast to systemic lupus erythematosus, systemic sclerosis, or dermatomyositis, and special care is needed not to misdiagnose SS when we see patients with common skin diseases such as drug eruption, infectious skin disease, or xerosis in daily practice. In contrast to SS, the reduced sweating function seen in atopic dermatitis (AD) is restricted only to axon reflex-induced indirect sweating, which is usually restored to normal levels after improvement of the dermatitis. Therefore, the xerotic skin lesions seen in SS and AD might be attributable to different pathomechanisms with similar dry skin manifestations. It is well known that dry skin is occasionally seen in SS, and clinical use of muscarinic M3-receptor agonists occasionally improves this condition through recovery of sweating function. Therefore, this M3-receptor agonist might be a promising drug and should be evaluated for the treatment of impaired sweating in AD complicated with or without SS.