CTICasesDiaphragmatic Myositis
Imaging findings
PET/CT in a 65-year-old male with dermatomyositis shows marked, symmetric thickening (hypertrophy) and intense FDG avidity (SUV max 5) of the diaphragmatic crura and dome. There is no pulmonary fibrosis, and follow-up PET/CT shows resolution of the diaphragmatic uptake with stable thickness. The patient also has paraspinal muscle atrophy.
Key takeaways
Involvement of the respiratory muscles, including the diaphragm, is a well-recognized but under-diagnosed feature of dermatomyositis and polymyositis. Active diaphragmatic myositis can present as diaphragmatic swelling (hypertrophy) and intense FDG uptake on PET, mimicking malignancy. The symmetric nature and lack of a discrete mass, along with response to immunosuppressive therapy, are characteristic.
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