title: Subclinical myositis is common in primary Sjögren's syndrome and is not related to muscle pain.
abstract: OBJECTIVE
  Although muscle pain is common in primary Sjögren's syndrome (SS), the underlying mechanisms are mainly unknown. We studied all patients with SS at our rheumatology unit with respect to muscle pain in general and to fibromyalgia (FM), and correlated clinical data to muscle biopsy findings.
  
  
  METHODS
  We investigated 48 patients with SS according to the modified European diagnostic criteria. The ACR criteria for FM were used to subgroup the patients. Muscle biopsy was performed in 36 patients. Light microscope morphology and immunohistochemical expression of MHC class I, MHC class II, and membrane attack complex (MAC) were studied.
  
  
  RESULTS
  We found 44% of patients complained of muscle pain; 27% fulfilled the ACR criteria for FM, whereas 17% had other forms of myalgia. Muscle pain could not be related to histopathological findings. Signs of inflammation were found in 26 of 36 biopsies (72%), and inflammation combined with degeneration/regeneration (i.e., histological signs of polymyositis) in 17 biopsies (47%). However, only 5 patients (14%) had clinical as well as histological signs of polymyositis. Eight muscle biopsies (22%) showed histological features of inclusion body myositis (IBM). However, no patient had clinical symptoms suggestive of this disease. Abnormal expression of MHC class I, MHC class II, and MAC was found in 18 (50%), 16 (44%), and 27 (75%) patients, respectively.
  
  
  CONCLUSIONS
  Muscle pain, especially FM, is common in SS. Histopathological signs of myositis are very common in SS. However, muscle symptoms are not related to histological signs of muscle inflammation. IBM-like findings may represent vacuolar myopathic degeneration due to previous subclinical muscle inflammation rather than a specific clinical entity.
authors.affiliation: Department of Clinical Neurosciences and Locomotion, University Hospital, Linköping, Sweden. Bjorn.Lindvall@lio.se
authors.forename: Bjorn
authors.initials: B
authors.lastname: Lindvall
authors.forename: Ann
authors.initials: A
authors.lastname: Bengtsson
authors.forename: Jan
authors.initials: J
authors.lastname: Ernerudh
authors.forename: Per
authors.initials: P
authors.lastname: Eriksson
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D015938:Complement Membrane Attack Complex / Q000276:immunology; D004185:Disability Evaluation; D005260:Female; D005356:Fibromyalgia / Q000150:complications / Q000276:immunology / Q000473:pathology; D006304:Health Status; D015395:Histocompatibility Antigens Class I / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D006801:Humans; D007124:Immunoenzyme Techniques; D007407:Interviews as Topic; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000473:pathology / Q000503:physiopathology; D009220:Myositis / Q000209:etiology* / Q000276:immunology / Q000473:pathology; D010146:Pain / Q000209:etiology* / Q000276:immunology / Q000503:physiopathology; D011788:Quality of Life; D012720:Severity of Illness Index; D012859:Sjogren's Syndrome / Q000150:complications* / Q000276:immunology / Q000473:pathology
chemical_list: D015938:Complement Membrane Attack Complex; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II