Clinical Investigation| Volume 348, ISSUE 2, P162-166, August 2014

Electrophysiological and Clinical Examination of Polymyositis: A Retrospective Analysis



      We retrospectively analyzed electromyogram (EMG), laboratory and clinical data of 93 patients with polymyositis (PM) to help improve early diagnostic accuracy.


      Data were collected from hospitalized patients who were diagnosed with PM between January 1, 2006 and April 1, 2010 at Chinese People’s Liberation Army General Hospital.


      Eighty-six (92.47%) patients exhibited an isolated myopathic EMG pattern, 3 (3.23%) showed myopathy combined with neuropathy and 1 (1.08%) had diabetes mellitus. Among the 4 without myopathic EMG, 1 had inflammatory myopathy, and 3 had prior corticosteroid treatment with clinical improvement before EMG examination. Muscle biopsy, performed in 40 cases, inclusive of the 7 cases that did not show an isolated myopathic EMG patterns, revealed that 80% exhibited typical pathological features of PM, 17.5% showed nonspecific muscle fiber necrosis and 2.5% were normal. EMG showed that tibialis anterior and biceps brachii exhibited more abnormal EMG results than abductor pollicis brevis. Patients with disease duration >3 months had significantly higher alanine aminotransferase and reduced motor unit potential (MUP) amplitudes compared to patients with shorter disease duration. statistical analysis revealed a significant association between disease duration and MUP amplitude reduction. Patients without interstitial lung disease showed significantly longer disease duration and higher creatine kinase and lactate dehydrogenase levels than patients with interstitial lung disease.


      our results show that MUP is a sensitive yardstick for diagnosis of PM and is inversely related to disease duration. our study also highlights that selecting specific muscles for EMG may improve diagnostic accuracy in PM.

      Key Indexing Terms

      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to The American Journal of the Medical Sciences
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Bohan A.
        • Peter J.B.
        Polymyositis and dermatomyositis (second of two parts).
        N Engl J Med. 1975; 292: 403-407
        • Dalakas M.C.
        Autoimmune muscular pathologies.
        Neurol Sci. 2005; 26: S72-S81
        • Wilson F.C.
        • Ytterberg S.R.
        • St Sauver J.L.
        • et al.
        Epidemiology of sporadic inclusion body myositis and polymyositis in Olmsted County, Minnesota.
        J Rheumatol. 2008; 35: 445-447
        • Lynn S.J.
        • Sawyers S.M.
        • Moller P.W.
        • et al.
        Adult-onset inflammatory myopathy: North Canterbury experience 1989–2001.
        Intern Med J. 2005; 35: 170-173
        • Neumann J.
        • Bilzer T.
        Evidence for MHC I-restricted CD8+ T-cell-mediated immunopathology in canine masticatory muscle myositis and polymyositis.
        Muscle Nerve. 2006; 33: 215-224
        • Nagaraju K.
        • Lundberg I.E.
        Inflammatory diseases of muscle and other myopathies.
        in: Firestein G.S. Budd R.C. Gabriel S.E. Kelley’s Textbook of Rheumatology. 9th ed. Saunders Elsevier, Philadelphia, PA2012 (chap 85)
        • Miller F.W.
        Polymyositis and dermatomyositis.
        in: Goldman L. Schafer A.I. Cecil Medicine. 24th ed. Saunders Elsevier, Philadelphia, PA2011 (chap 277)
        • Waclawik A.J.
        • Fadic R.
        • Lotz B.P.
        • et al.
        CD8 and CD4 T cell-mediated polymyositis complicating the HTLV-1 associated myelopathy: quantitative evaluation of corticosteroid treatment.
        Acta Neurol Scand. 1996; 94: 115-119
        • Uchino M.
        • Araki S.
        • Yoshida O.
        • et al.
        High single-dose alternate-day corticosteroid regimens in treatment of polymyositis.
        J Neurol. 1985; 232: 175-178
        • Mitz M.
        • Chang G.J.
        • Albers J.W.
        • et al.
        Electromyographic and histologic paraspinal abnormalities in polymyositis/dermatomyositis.
        Arch Phys Med Rehabil. 1981; 62: 118-121
        • Prieto S.
        • Grau J.M.
        The geoepidemiology of autoimmune muscle disease.
        Autoimmun Rev. 2010; 9: A330-A334
        • Rostić G.
        • Paunić Z.
        • Vojvodić D.
        • et al.
        Systemic lupus erythematosus and dermatomyositis—case report [in Serbian].
        Srp Arh Celok Lek. 2005; 133: 137-140
        • Voermans N.C.
        • Pillen S.
        • de Jong E.M.
        • et al.
        Morphea profunda presenting as a neuromuscular mimic.
        J Clin Neuromuscul Dis. 2008; 9: 407-414
        • Holmes M.V.
        • Ioannou Y.
        • Borysiewicz C.
        • et al.
        Juvenile dermatomyositis with Sjögren’s syndrome.
        Clin Rheumatol. 2008; 27: S3-S5
        • Yoshidome Y.
        • Morimoto S.
        • Tamura N.
        • et al.
        A case of polymyositis complicated with myasthenic crisis.
        Clin Rheumatol. 2007; 26: 1569-1570
        • Volochayev R.
        • Csako G.
        • Wesley R.
        • et al.
        Laboratory test abnormalities are common in polymyositis and dermatomyositis and differ among clinical and demographic groups.
        Open Rheumatol J. 2012; 6: 54-63
        • Uncini A.
        • Lange D.J.
        • Lovelace R.E.
        • et al.
        Long-duration polyphasic motor unit potentials in myopathies: a quantitative study with pathological correlation.
        Muscle Nerve. 1990; 13: 263-267
        • Blijham P.J.
        • Hengstman G.J.
        • Hama-Amin A.D.
        • et al.
        Needle electromyographic findings in 98 patients with myositis.
        Eur Neurol. 2006; 55: 183-188
        • Song Y.Q.
        • Shen D.G.
        The analysis of clinical outcomes and EMG of polymyositis and dermatomyositis patients.
        J Clin Neurol Electrophysiol. 2002; 11: 217-219
        • Choy E.H.
        • Isenberg D.A.
        Treatment of dermatomyositis and polymyositis.
        Rheumatology (Oxford). 2002; 41: 7-13
        • Dalakas M.C.
        Therapeutic approaches in patients with inflammatory myopathies.
        Semin Neurol. 2003; 23: 199-206
        • Chen F.
        • Shu X.M.
        • Wang D.X.
        • et al.
        Measurement and clinical significance of serum monocyte chemo-attractant protein-1 in patients with polymyosits/dermatomyosits [in Chinese].
        Beijing Da Xue Xue Bao. 2012; 44: 204-208
        • Shen H.
        • Xia L.
        • Lu J.
        Pilot study of interleukin-27 in pathogenesis of dermatomyositis and polymyositis: associated with interstitial lung diseases.
        Cytokine. 2012; 60: 334-337
        • Peng Q.L.
        • Xie Y.
        • Zhang R.F.
        • et al.
        The levels and clinical significance of serum B cell activating factor in Chinese patients with polymyositis or dermatomyositis [in Chinese].
        Zhonghua Nei Ke Za Zhi. 2012; 51: 210-213
        • Laraki R.
        • Bletry O.
        • Agbalika F.
        • et al.
        Do neuromyositis exist?.
        Ann Med Interne. 1994; 145: 88