283 Quantifying muscle amyloid in inclusion body myositis using pet

ObjectivesInclusion body myositis (IBM) shares some histopathological features with polymyositis (PM). Current investigations have low sensitivity for identification of amyloid deposits that are characteristic of IBM, contributing to frequent misdiagnosis. We compared muscle amyloid content, quantified using a novel positron emission tomography (PET) technique, in IBM and PM.MethodsTen cases with IBM and six controls with PM underwent clinical review, [18F]florbetapir PET/computed tomography, and magnetic resonance imaging (MRI) of whole-body skeletal musculature. [18F]florbetapir standardised uptake value ratios (SUVRs, reference=lumbar fat pad) in skeletal muscle were compared between cases and controls. The relationship in IBM of [18F]florbetapir SUVRs to clinical and MRI-derived measures of disease severity were also investigated.Results[18F]florbetapir SUVRs were significantly higher in those with IBM for all muscle regions assessed (total SUVR 1.45 [IQR 1.28–2.05] versus 1.01 [IQR 0.80–1.22], p=0.005). Strong negative correlation between MRI-derived muscle inflammation levels and [18F]florbetapir SUVRs were observed only in calf muscles bilaterally (right −0.73, p=0.02; left −0.68, p=0.03). No significant relationship between [18F]florbetapir SUVRs and clinical measures of disease severity were identified.ConclusionMuscle amyloid imaging using [18F]florbetapir PET may be useful in the diagnostic workup of IBM, particularly when differentiating from PM.