Imaging
Dermatomyositis/Polymyositis
- Preliminary Diagnosis: Dermatomyositis/Polymyositis
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I. What imaging technique is first-line for this diagnosis?
- II. Describe the advantages and disadvantages of this technique for diagnosing dermatomyositis/polymyositis.
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III. What are the contraindications for the first-line imaging technique?
-
IV. What alternative imaging techniques are available?
- V. Describe the advantages and disadvantages of the alternative techniques for diagnosing dermatomyositis/polymyositis.
- VI. What are the contraindications for the alternative imaging techniques?
Preliminary Diagnosis: Dermatomyositis/Polymyositis
I. What imaging technique is first-line for this diagnosis?
MRI without gadolinium. T2 weighted or STIR sequences are the most sensitive of the MRI sequences.
II. Describe the advantages and disadvantages of this technique for diagnosing dermatomyositis/polymyositis.
Advantages
May be diagnostic in the correct clinical scenario.
Can detect the fatty muscular atrophy, which occurs over the disease’s natural history, and fascial thickening.
Can detect other causes of muscle pain and weakness, including contusions, infection, and radiation induced myosits.
Does not use ionizing radiation.
Disadvantages
Expensive.
Time consuming.
Requires significant patient cooperation.
III. What are the contraindications for the first-line imaging technique?
Contraindicated in patients with non-MR compatible metallic hardware or foreign bodies.
IV. What alternative imaging techniques are available?
CT without contrast.
Plain film radiography.
V. Describe the advantages and disadvantages of the alternative techniques for diagnosing dermatomyositis/polymyositis.
CT without contrast
Advantages
May quickly and accurately identify the calcifications that occur in nearly half of the patients afflicted with chronic dermatomyositis/polymyositis.
May be much quicker than MR imaging.
Requires less patient cooperation than MR.
CT of the chest is sensitive for detecting interstitial lung disease, which may accompany this disease.
Disadvantages
Exposes the patient to a large amount of non-ionizing radiation.
Lacks the anatomical detail afforded by MRI.
Less sensitive compared to MRI for detecting intramuscular, permuscular, or subcutaneous edema.
Plain radiographs
Advantages
Can quickly identify subcutaneous, muscular, and fascial calcifications, osteoporosis, and muscular atrophy in a cost effective manner.
Involves significantly less ionizing radiation exposure compared to CT.
Disadvantages
Very nonspecific.
Limited to detection of calcification, which only occurs in 25-50% of patients with longstanding disease.
Not sensitive for detecting intramuscular, subcutaneous, and perimuscular edema.
Plain film utilizes ionizing radiation.
VI. What are the contraindications for the alternative imaging techniques?
CT without contrast
Contraindicated in pregnant women, especially during the first two trimesters.
Plain radiographs
No significant contraindications exist.
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