Dermatomyositis/Polymyositis

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.