The diagnosis and classification of polymyositis.
Polymyositis is classified as a separate entity among idiopathic inflammatory myopathies but it is considered as the least common since it is an exclusion diagnosis. This myopathy usually presents with subacute-chronic symmetric proximal limb weakness, although some extramuscular manifestations are common. Creatine kinase values may be increased up to 50-fold in active disease. Muscle biopsy is characterized by endomysial inflammatory infiltrate consisting predominantly of CD8+ T cells that invade healthy muscle fibres expressing the MHC-I antigen. Although serum autoantibodies, EMG and imaging techniques can help in diagnosis, muscle histopathology is a pivotal value. The clinical picture together with the pathological findings confers the also called PM pattern. A broad differential diagnosis is needed before concluding a diagnosis of pure PM. Sporadic inclusion-body myositis, toxic, endocrine and metabolic myopathies as well as muscular dystrophies are the major categories to be ruled out. Finally, a diagnostic algorithm for suspected cases of PM is also proposed.
Muscle Research Unit, Internal Medicine Service, Hospital Clínic de Barcelona, Villarroel 170, 08036 Barcelona, Spain; Fundació Cellex, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain. Electronic address: jcmilise@clinic.ub.es.
J C
JC
Milisenda
Internal Medicine Service, Hospital Vall d'Hebrón, Barcelona, Spain. Electronic address: aselva@vhebron.net.
A
A
Selva-O'Callaghan
Muscle Research Unit, Internal Medicine Service, Hospital Clínic de Barcelona, Villarroel 170, 08036 Barcelona, Spain; Fundació Cellex, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain. Electronic address: jmgrau@clinic.ub.es.
J M
JM
Grau
D000208:Acute Disease; D001323:Autoantibodies / Q000096:biosynthesis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000473:pathology / Q000821:virology; D002908:Chronic Disease; D003937:Diagnosis, Differential; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis; D006801:Humans; D007111:Immunity, Cellular; D007249:Inflammation / Q000145:classification / Q000175:diagnosis; D008264:Macrophages / Q000276:immunology / Q000473:pathology / Q000821:virology; D017285:Polymyositis / Q000145:classification* / Q000175:diagnosis* / Q000276:immunology
D001323:Autoantibodies; D015395:Histocompatibility Antigens Class I
Idiopathic inflammatory myopathies; Polymyositis