By Björn Falck (Turku, Finland), Erik Stålberg (Uppsala, Sweden)




●  cell mediated autoimmune response against muscle fibers

Clinical features

●  incidence 1-9/1000000

●  more common in women than men

●  usually begins after the age of 20 years

●  muscle weakness develops subacutely or insidiously

●  proximal limb and neck flexor muscles involved more than other muscles

●  muscle pain is sometimes present, but it is not as prominent as one would expect

●  dysphagia is common in polymyositis

●  CK is usually moderately elevated


●  demonstrate myopathy

●  assess: severity (mild, moderate, severe) and activity (stationary, active)

Expected abnormal findings


●  fibrillations in the acute stage, they disappear in remission

●  small, brief MUPs in the acute stage

●  later long duration polyphasic MUPs in the chronic stage


●  if distal muscles are severely involved MCS ampl are reduced

Expected normal findings


●  SCS

●  MCS



●  m.vastus lateralis/m.vastus medialis

●  m.deltoideus/m.biceps

●  m.interosseus dorsalis I/m.abductor digiti minimi

●  m.tibialis anterior

●  paravertebral muscles in the low thoracic region should be studied if limb muscles do not show distinct abnormalities


●  MCS: n.medianus and n.peroneus unilaterally

●  SCS: n.radialis and n.suralis unilaterally


●  in chronic PM, there may be a mixed pattern of small and large MUPs

●  it is not unusual for patients with PM to have concurrent PNP, especially if they have malabsorption



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