Paraspinal Muscle Atrophy in Axial Spondyloarthritis

Imaging Features and Diagnosis

MRI is the gold standard for evaluating both inflammatory changes and muscle atrophy in axSpA patients, with T1-weighted sequences showing muscle volume loss and fatty replacement, and fluid-sensitive sequences (STIR or T2-weighted fat-suppressed) demonstrating active inflammatory changes, as recommended by the American College of Radiology 2, 3, 4, 5
CT may be helpful in patients unable to undergo MRI, showing muscle volume loss, fatty infiltration of paraspinal muscles, and associated bone erosions and structural changes, with evidence from the American College of Radiology 1, 2, 4
Conventional radiography has limited value in directly assessing muscle atrophy but may show syndesmophytes and other structural changes of the spine, and sacroiliitis and SI joint abnormalities, according to the American College of Radiology 1, 3

Paraspinal muscle atrophy in axSpA is associated with disease progression and structural damage, contributes to functional limitations, decreased mobility, and impaired quality of life, and may be more prevalent in advanced stages of axSpA, as reported by the American College of Radiology 1, 3, 6
The American College of Radiology recommends that paraspinal muscle atrophy be considered a factor in disease progression and treatment planning 1, 3

Early diagnosis and treatment of axSpA may help prevent or minimize muscle atrophy, and anti-TNF-α and other biologic therapies for axSpA may help reduce inflammation and potentially slow muscle atrophy progression, according to the American College of Radiology and the National Institute of Rheumatology 3, 6, 7, 8
The American College of Radiology recommends regular imaging follow-up (typically no more frequently than every 2 years) to monitor disease progression and muscle changes 5

Muscle atrophy may be present even in early or non-radiographic axSpA, though it's more common in advanced disease, and differential diagnosis should include other causes of muscle atrophy, as noted by the American College of Radiology 3, 4, 5
The American College of Radiology recommends that when requesting MRI to evaluate for axSpA and muscle atrophy, specify the need for appropriate sequences (including fat-suppressed fluid-sensitive sequences) 5