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Polymyositis Workup

  • Author: Ramesh Pappu, MD, DPH, MBBS; Chief Editor: Herbert S Diamond, MD  more...
 
Updated: Nov 06, 2015
 

Approach Considerations

The following laboratory findings may be present in polymyositis:

  • Complete blood count (CBC) - May show leukocytosis or thrombocytosis; leukocytosis is present in more than 50% of patients
  • Erythrocyte sedimentation rate or C-reactive protein level - Elevated in 50% of patients with polymyositis
  • Elevated muscle enzyme levels
  • Myoglobinuria
  • Autoantibodies
  • Positive rheumatoid factor results - Found in more than 50% of patients

Perform age-appropriate evaluation for malignancy. Testing for associated malignancy is based on age and sex and can be performed using imaging techniques such as chest radiography, computed tomography (CT) scanning, mammography, pelvic ultrasonography, and upper and lower gastrointestinal endoscopy.

Pulmonary function tests and diffusion capacity for evaluation of interstitial lung disease may be appropriate.

Muscle enzyme levels

Serum creatine kinase (CK) levels are usually elevated in persons with polymyositis, ranging from 5-50 times the reference range. A level greater than 100 times the reference level is rare and is a signal of other diagnoses.

Serum CK levels, along with careful physical examination, may be used to monitor myositis activity. However, serum CK levels may be within reference ranges despite increased disease activity (eg, in cases of chronic and late-stage polymyositis). CK levels are usually minimally elevated or within the reference range in patients with inclusion body myositis. CK levels are within the reference range in patients with corticosteroid-induced myopathy.

Other muscle enzymes that may be elevated include the following:

  • Lactic dehydrogenase
  • Aspartate aminotransferase
  • Alanine aminotransferase
  • Aldolase - In practice, usually only the CK and aldolase levels are determined

Antibody findings

The following antibody findings may exist in polymyositis:

  • Antinuclear antibody assay - Positive in one third of patients with polymyositis and in only 15% of patients with inclusion body myositis
  • Myositis-specific antibodies
  • Antisynthetase antibodies (such as anti-Jo-1 antibodies) - Associated with certain clinical features; antisynthetase syndrome may manifest as idiopathic inflammatory myopathy, interstitial lung disease, arthritis, Raynaud phenomenon, fever, and/or mechanic's hands
  • Signal-recognition particle (SRP) antibodies - Approximately 4% of patients with polymyositis have antibodies to signal recognition particles (SRPs), which are associated with acute onset of severe weakness, increased incidence of cardiac involvement, and higher mortality rates
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Imaging Studies

Muscle-imaging techniques such as magnetic resonance imaging (MRI) and ultrasonography may be useful to document and localize the extent of muscle involvement. MRI scans show signal intensity abnormalities of muscle due to inflammation, edema, or scarring. (See the image below.)

MRI of thighs showing increased signal in the quad MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.

MRI scans may also be used to guide muscle biopsy and to monitor disease activity. However, many clinicians choose the biopsy site on the basis of findings at electromyography and clinical examination and believe that MRI is not required. Barium swallow studies are helpful for evaluation of dysphagia or dysphonia.

Chest radiography and high-resolution CT scanning of the chest are helpful for the evaluation of interstitial lung disease. CT scanning of the chest, abdomen, and pelvis is considered for screening of associated malignancy. Chest radiography may also reveal evidence of associated malignancy.

Also consider mammography, pelvic ultrasonography, and upper and lower GI endoscopy in screening for associated malignancy.

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Electromyography

Electromyographic findings are abnormal in almost all patients (90%) with polymyositis. Various abnormalities consistent with polymyositis may be found, depending on the stage of disease. In patients with inclusion body myositis, the following myopathic and neuropathic changes may be present:

  • Evidence of membrane irritability, increased insertional activity, fibrillation potentials, positive sharp waves at rest
  • Myopathic changes of motor unit action potential; decreased amplitude and duration; increased polyphasic potentials; bizarre, high-frequency, repetitive discharges
  • Chronic changes, evidence of denervation-reinnervation
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Biopsy

Muscle biopsy is crucial in helping to diagnose polymyositis and in excluding other rare muscle diseases.[12] MRI can be used to guide the site of biopsy. However, many clinicians choose the biopsy site on the basis of findings at electromyography and clinical examination and believe that MRI is not required.

Avoid biopsy of sites recently studied by EMG by using the contralateral side. Inflammatory changes are seen at muscle biopsy (eg, deltoid or quadriceps femoris). Findings occasionally may be normal because of patchy involvement. (See the images below.)

Hematoxylin and eosin frozen section shows polymyo Hematoxylin and eosin frozen section shows polymyositis. Endomysial chronic inflammation is present among intact myofibers, which are remarkable only for increased variability of fiber size. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Patient had dense endomysial inflammation that contains an abundance of plasma cells, which can be observed in patients with chronic polymyositis. Two necrotic myofibers, characterized by dense eosinophilic staining, are observed. Focal fatty infiltration of the muscle is present in the lower left quadrant of the photomicrograph. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Photomicrograph illustrates attack on a nonnecrotic myofiber by autoaggressive T lymphocytes. On the left, the central myofiber is intact. On the right, it is obliterated by a segmental inflammatory attack. If immunohistochemistry were performed, expected findings would include an admixture of CD8 T lymphocytes and macrophages in the inflammatory process. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polym Hematoxylin and eosin paraffin section shows polymyositis. Longitudinal section shows a dense, chronic, endomysial inflammatory infiltrate. Image courtesy of Roberta J. Seidman, MD.
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Histologic Findings

Muscle biopsy shows muscle fibers in varying stages of inflammation, necrosis, and regeneration. Findings include focal endomysial infiltration by mononuclear cells (consisting of mostly CD8+ T lymphocytes and macrophages), capillary obliteration, endothelial cell damage, and increased amounts of connective tissue. Later in the course of polymyositis, muscle-cell degeneration, fibrosis, and regeneration may be observed. (See the images below.)

Histopathology of polymyositis showing endomysial Histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.
Close view of muscle biopsy, showing chronic infla Close view of muscle biopsy, showing chronic inflammatory infiltrate consisting of T lymphocytes, especially CD8+ T lymphocytes.

Because the inflammatory infiltrates can be small and multifocal, they can be missed in a small muscle-biopsy specimen. Perifascicular atrophy or prominent perivascular infiltrates are not present, and the blood vessels are normal. When the disease becomes chronic, the connective tissue increases. The diagnosis of polymyositis is definite when a patient has subacute, elevated levels of serum CK and findings on muscle biopsy consistent with the histologic features of polymyositis.

Inclusion body myositis is histologically similar to polymyositis, with the additional presence of intracytoplasmic inclusion bodies observed on electron microscopy. Dermatomyositis shows inflammatory changes, predominantly in the perimysial and perivascular regions with CD4+ T and B lymphocytes (see the image below). Corticosteroid-induced myopathy causes no inflammatory changes. Type II fiber atrophy is the characteristic feature.

Hematoxylin and eosin paraffin shows dermatomyosit Hematoxylin and eosin paraffin shows dermatomyositis. In dermatomyositis, inflammation is characteristically perivascular and perimysial. Vessel oriented approximately vertically in the center has a mild perivascular chronic inflammatory infiltrate. The endothelium is plump. The wall is not necrotic. A few lymphocytes in the wall of the vessel are probably in transit from the lumen to the external aspect of the vessel. Some observers may interpret this finding as vasculitis, but it is certainly neither necrotizing vasculitis nor arteritis. Image courtesy of Roberta J. Seidman, MD.
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Contributor Information and Disclosures
Author

Ramesh Pappu, MD, DPH, MBBS Adjunct Associate Professor of Medicine, Drexel University College of Medicine

Ramesh Pappu, MD, DPH, MBBS is a member of the following medical societies: American College of Rheumatology, American Association of Physicians of Indian Origin

Disclosure: Nothing to disclose.

Coauthor(s)

Mythili Seetharaman, MD Consultant Rheumatologist, OAA; Clinical Assistant Professor, Thomas Jefferson University Hospital, St Christopher's Hospital for Children

Mythili Seetharaman, MD is a member of the following medical societies: American College of Rheumatology, American Medical Association

Disclosure: Nothing to disclose.

Chief Editor

Herbert S Diamond, MD Visiting Professor of Medicine, Division of Rheumatology, State University of New York Downstate Medical Center; Chairman Emeritus, Department of Internal Medicine, Western Pennsylvania Hospital

Herbert S Diamond, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, American College of Rheumatology, American Medical Association, Phi Beta Kappa

Disclosure: Nothing to disclose.

Acknowledgements

Michael S Beeson, MD, MBA, FACEP, Professor of Emergency Medicine, Northeastern Ohio Universities College of Medicine and Pharmacy; Attending Faculty, Akron General Medical Center

Michael S Beeson, MD, MBA, FACEP is a member of the following medical societies: American College of Emergency Physicians, Council of Emergency Medicine Residency Directors, National Association of EMS Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Thomas H Brannagan III, MD, Associate Professor of Clinical Neurology and Director, Peripheral Neuropathy Center, Columbia University, College of Physicians and Surgeons; Co-Director, EMG Laboratory, New York-Presbyterian Hospital, Columbia Campus, New York

Thomas H Brannagan III, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Peripheral Nerve Society

Disclosure: Nothing to disclose.

Lawrence H Brent, MD, Associate Professor of Medicine, Jefferson Medical College of Thomas Jefferson University; Chair, Program Director, Department of Medicine, Division of Rheumatology, Albert Einstein Medical Center

Lawrence H Brent, MD is a member of the following medical societies: American Association for the Advancement of Science, American Association of Immunologists, American College of Physicians, and American College of Rheumatology

Disclosure: Genentech Honoraria Speaking and teaching; Genentech Grant/research funds Other; Amgen Honoraria Speaking and teaching; Pfizer Honoraria Speaking and teaching; Abbott Immunology Honoraria Speaking and teaching; Takeda Honoraria Speaking and teaching; UCB Speaking and teaching; Omnicare Consulting fee Consulting; Centocor Consulting fee Consulting

Zaineb Daud, MD, Consulting Staff, Department of Neurology, Medical College of Pennsylvania Hahnemann University

Disclosure: None

Gino A Farina, MD, FACEP, FAAEM, Associate Professor of Clinical Emergency Medicine, Albert Einstein College of Medicine; Program Director, Department of Emergency Medicine, Long Island Jewish Medical Center

Gino A Farina, MD, FACEP, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Francisco de Assis Aquino Gondim, MD, MSc, PhD, Associate Professor of Neurology, Department of Neurology and Psychiatry, St Louis University School of Medicine

Francisco de Assis Aquino Gondim, MD, MSc, PhD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Movement Disorders Society

Disclosure: Nothing to disclose.

Aamir Hashmat, MD, Consulting Staff, Neurology and Neurodiagnostics Lab, Department of Neurology, Jeff Anderson Regional Medical Center

Aamir Hashmat, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society; American Medical Association, AO Foundation

Disclosure: None

Milind J Kothari, DO, Professor and Vice-Chair, Department of Neurology, Pennsylvania State University College of Medicine; Consulting Staff, Department of Neurology, Penn State Milton S Hershey Medical Center

Milind J Kothari, DO is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Neurological Association

Disclosure: Nothing to disclose.

Kristine M Lohr, MD, MS, Professor, Department of Internal Medicine, Center for the Advancement of Women's Health and Division of Rheumatology, Director, Rheumatology Training Program, University of Kentucky College of Medicine

Kristine M Lohr, MD, MS is a member of the following medical societies: American College of Physicians, American College of Rheumatology, and American Medical Women's Association

Disclosure: Nothing to disclose.

Glenn Lopate, MD, Associate Professor, Department of Neurology, Division of Neuromuscular Diseases, Washington University School of Medicine; Director of Neurology Clinic, St Louis ConnectCare; Consulting Staff, Department of Neurology, Barnes-Jewish Hospital

Glenn Lopate, MD is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Nicholas Lorenzo, MD, Consulting Staff, Neurology Specialists and Consultants

Nicholas Lorenzo, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Neurology

Disclosure: Nothing to disclose.

Henry Rosenkranz, MD, FAAEM, FACEP, Department of Emergency Medicine, Norwood Hospital

Henry Rosenkranz, MD, FAAEM, FACEP is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians

Disclosure: Nothing to disclose.

Erik D Schraga, MD, Staff Physician, Department of Emergency Medicine, Mills-Peninsula Emergency Medical Associates

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Reference Salary Employment

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MRI of thighs showing increased signal in the quadriceps muscles bilaterally consistent with inflammatory myositis.
Histopathology of polymyositis showing endomysial mononuclear inflammatory infiltrate and muscle fiber necrosis.
Close view of muscle biopsy, showing chronic inflammatory infiltrate consisting of T lymphocytes, especially CD8+ T lymphocytes.
Hematoxylin and eosin frozen section shows polymyositis. Endomysial chronic inflammation is present among intact myofibers, which are remarkable only for increased variability of fiber size. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polymyositis. Patient had dense endomysial inflammation that contains an abundance of plasma cells, which can be observed in patients with chronic polymyositis. Two necrotic myofibers, characterized by dense eosinophilic staining, are observed. Focal fatty infiltration of the muscle is present in the lower left quadrant of the photomicrograph. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polymyositis. Photomicrograph illustrates attack on a nonnecrotic myofiber by autoaggressive T lymphocytes. On the left, the central myofiber is intact. On the right, it is obliterated by a segmental inflammatory attack. If immunohistochemistry were performed, expected findings would include an admixture of CD8 T lymphocytes and macrophages in the inflammatory process. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin shows dermatomyositis. In dermatomyositis, inflammation is characteristically perivascular and perimysial. Vessel oriented approximately vertically in the center has a mild perivascular chronic inflammatory infiltrate. The endothelium is plump. The wall is not necrotic. A few lymphocytes in the wall of the vessel are probably in transit from the lumen to the external aspect of the vessel. Some observers may interpret this finding as vasculitis, but it is certainly neither necrotizing vasculitis nor arteritis. Image courtesy of Roberta J. Seidman, MD.
Hematoxylin and eosin paraffin section shows polymyositis. Longitudinal section shows a dense, chronic, endomysial inflammatory infiltrate. Image courtesy of Roberta J. Seidman, MD.
 
 
 
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