Myopathy in Autoimmune Diseases – Primary Sjögren’s Syndrome and Dermatomyositis

Myopathy, which clinically shows muscular pain (myalgia), weakness, cramps, stiffness and spasm, is one of neuromuscular disorders due to inflammation and/or dysfunction of muscle fibers. “Myositis”, which is a general term for inflammation of the muscle, is pathologically an inflammatory myopathy seen seen mainly in autoimmune disorders including dermatomyositis (DM). The myopathy is classified by National Institute of Neurological Disorders and Stroke (NINDS) as indicated in Table 1 (1). We here focus myopathy on primary Sjögren’s syndrome (pSjS) associated with myalgia “mimicking DM”, as previously reported (2), and the inflammatory myopathy of DM (Table 2). Most of SjS is a secondary disorder to systemic autoimmune diseases including systemic lupus erythematosus (SLE), systemic sclerosis, DM, and so on. However, SjS, which is not associated with other autoimmune diseases, is considered to be an idiopathic primary disorder characterized by sicca symptoms. It is known that pSjS may be associated with fever, fatigue, myalgia, arthralgia, cutaneous vasculitis, etc. in addition to sicca symptoms (4-8).