Shilpa Pandey MD, Presenter: Nothing to Disclose

Stacy Elaine Smith MD, Abstract Co-Author: Nothing to Disclose

sIBM is a poorly understood immune disorder yet is the most common muscle disorder of aging in patients over 50. We describe the characteristic MR appearance of muscle involvement in sIBM with clinical correlation.

Patients with mm biopsy confirmed sIBM & MRI of their extremities at our institution were included. Demographic data included age,gender,degree & site of weakness, & length of disease process. Surgical pathology results & CK levels were recorded. MR images were reviewed by 2 MSK radiologists wagreement by consensus. MR evaluation features included distribution of muscle involvement, presence & extent of atrophy, fatty infiltration, & edema/ inflammatory changes.

9 patients (5F;4M) age 45-78 yrs (mean 65.8yrs) were included.89% presented w quadriceps mm weakness, all w slow progression & upper extremity flexor weakness over time( 1 pt presented w hand grip weakness). Length of disease process:3-8 yrs(mean 5 yrs).100% had increased CK(>340)& mm bx confirmed IBM w rimmed vacuoles.9 bilateral thigh MRIs(PD & DWI post contrast) & 7 upper arm MR (PD noncontrast) were reviewed. Fatty atrophy/Infiltration:100% mild/mod bilateral distal med & lat vastus mm involvement w sparing of the rectus mm correlating w severity & length of disease;80% intermedius mm involvement; 56% mild/mod atrophy/fatty infiltration of the medial adductor or SM/ST mms. DWI post gad:89% mild/mod increased signal of the med/lat vastus mm w 33% mild/mod increased signal in SM/ST mms.Increased signal was noted in the med/lat vastus mms in 3 of 4 patients who had STIR images.Upper arm MR(PD imaging):3/9 mod distal triceps mm atrophy/infiltration,1/9 mod distal triceps & medial mm atrophy/infiltration (pt who presented with hand grip wkness),& 1/9 mild supraspinatous atrophy.

IBM is the most common inflammatory myopathy of aging characterized by asymmetric slow-onset muscle weakness & wasting of distal & anterior muscle groups in pts > 50 years. MR imaging demonstrates characteristic pattterns of mm atrophy, infiltration & edema on PD/T1 & fluid sensitive sequences & is paramount in initial diagnosis as well as treatment response & disease progression. Timely diagnosis of IBM is important because it is refractory to standard medical therapy used for other inflammatory myopathies.

Understanding the characteristic MR patterns of muscle involvement in sIBM is paramount in suggesting the diagnosis of this often overlooked disorder.

Pandey, S, Smith, S, MR Imaging Features of Sporadic Inclusion Body Myositis s(IBM).  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043657.html