Polymyositis-Dermatomyositis



Polymyositis-Dermatomyositis


Aqeel A. Chowdhry, MD

Tan-Lucien H. Mohammed, MD, FCCP





Key Facts


Terminology



  • Polymyositis: Autoimmune inflammatory myopathy (limb girdle & anterior neck muscles)


  • Dermatomyositis: Polymyositis + skin rash


Imaging Findings



  • Nonspecific, multiple patterns based on prevailing histology: NSIP, UIP, COP, DAD


  • Aspiration common and may alone result in pulmonary disease or be superimposed on other patterns


  • Hypoventilation also common and may result in atelectasis (discoid or long lines)


  • Distribution similar irrespective of pattern; primarily involves basilar lung


  • Dystrophic muscle calcification in polymyositis


  • Skin or subcutaneous calcifications in dermatomyositis


  • Whole-body turbo STIR helpful in demonstrating soft tissue inflammatory burden


Top Differential Diagnoses



  • Nonspecific Interstitial Pneumonitis


  • Cryptogenic Organizing Pneumonia


  • Idiopathic Pulmonary Fibrosis


  • Scleroderma


Clinical Issues



  • No established association between interstitial lung disease and extent of muscle or skin findings


  • Polymyositis: Weakness is painless in 66%


  • Dermatomyositis: Violaceous heliotrope rash over anterior edge of upper eyelids







Frontal radiograph shows nonspecific interstitial pneumonitis from polymyositis. Note the diffuse peripheral interstitial thickening image.






Axial HRCT shows subpleural ground-glass opacities and reticular opacities image. Traction bronchiectasis is out of proportion to reticular opacities. Note the NSIP pattern in polymyositis-dermatomyositis.


TERMINOLOGY


Abbreviations and Synonyms



  • Polymyositis-dermatomyositis (PM-DM), dermatomyositis-polymyositis (DM-PM), dermato-polymyositis (DPM)


  • Nonspecific interstitial pneumonia (NSIP), cryptogenic organizing pneumonia (COP), usual interstitial pneumonia (UIP), diffuse alveolar damage (DAD)


Definitions



  • Polymyositis: Autoimmune inflammatory myopathy (limb girdle & anterior neck muscles)


  • Dermatomyositis: Polymyositis + skin rash


IMAGING FINDINGS


General Features



  • Best diagnostic clue



    • Lung disease in patient with muscle weakness



      • Hint: Elevated diaphragms and subsegmental atelectasis


CT Findings



  • Nonspecific, multiple patterns based on prevailing histology: NSIP, UIP, COP, DAD



    • Aspiration common and may alone result in pulmonary disease or be superimposed on other patterns


    • Hypoventilation also common and may result in atelectasis (discoid or long lines)


  • Distribution similar irrespective of pattern; primarily involves basilar lung


  • NSIP



    • Ground-glass opacities > reticular opacities in bronchovascular distribution


    • Traction bronchiectasis out of proportion to reticular opacities


  • UIP



    • Reticular opacities and honeycombing in subpleural distribution


    • Traction bronchiectasis


  • COP



    • Subpleural focal areas of consolidation


    • Reverse halo sign


  • DAD




    • Acute diffuse ground-glass opacities often with traction bronchiectasis


  • Treatment



    • Ground-glass opacities, consolidation may resolve


  • Extrathoracic manifestations



    • Skin or subcutaneous calcifications in dermatomyositis


    • Dystrophic muscle calcification in polymyositis, uncommon


  • Other



    • High incidence of malignancy, particularly bronchogenic carcinoma


Radiographic Findings



  • 10% have normal chest radiographs


  • Lung volumes reduced



    • Elevated hemidiaphragms due to respiratory muscle weakness, atelectasis


  • Lungs



    • Nonspecific symmetric, basal reticular pattern of parenchymal involvement, may progress to honeycombing (less often)


    • Aspiration



      • Variable appearance, aspiration segments, waxing and waning opacities eventually resulting in fibrosis


  • Soft tissue calcifications



    • Often over bony prominences


    • More common in younger patients


Fluoroscopic Findings



  • Esophagram



    • Upper esophagus predominantly involved may result in reflux or aspiration


    • Swallowing studies useful for diet


    • Obstruction due to stricture or scarring, late


MR Findings



  • Whole body turbo STIR helpful in demonstrating soft tissue inflammatory burden


  • Musculature



    • Signal intensity abnormalities due to inflammation, edema, scarring


    • Symmetric involvement



      • Proximal lower limb girdle, early


      • Progression to proximal upper limb girdle, neck flexors, pharyngeal muscles


      • Facial muscles typically spared


    • Images may be used to guide muscle biopsy


Imaging Recommendations



  • Best imaging tool



    • CT: Affects patient prognosis by demonstrating extent of pulmonary involvement, chronicity of disease process, and response to treatment


    • MR imaging useful to demonstrate areas of muscular involvement


DIFFERENTIAL DIAGNOSIS


Nonspecific Interstitial Pneumonitis



  • NSIP pattern common in PM-DM


  • No muscle involvement or skin rash


Cryptogenic Organizing Pneumonia



  • COP pattern common in PM-DM


  • No muscle involvement or skin rash


Idiopathic Pulmonary Fibrosis



  • UIP pattern, seen in PM-DM


  • Older age group, no muscle involvement or skin rash


Scleroderma



  • NSIP pattern common


  • No muscle involvement or skin rash


  • Esophageal dilatation common, less common in PM-DM


Drug Toxicity



  • Review drug history


  • Commonly chemotherapy drugs (bleomycin, cyclophosphamide, nitrosoureas, etc.)


  • Can result in any pattern seen in PM-DM


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Sep 20, 2016 | Posted by in RESPIRATORY IMAGING | Comments Off on Polymyositis-Dermatomyositis

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