Cdj Sinclair

Skeletal muscle MRI magnetisation transfer ratio reflects clinical severity in peripheral neuropathies

MRI may provide treatment outcome measures in neuromuscular conditions. The authors assessed MRI magnetisation transfer ratios (MTRs) in lower-limb musculature as markers of pathology in peripheral neuropathies and compared the findings with associated clinical data. Ten patients with Charcot–Marie–Tooth disease type 1A (CMT1A) and nine patients with chronic inflammatory demyelinating polyneuropathy (CIDP) were compared with 10 healthy subjects. The MTR in the calf muscles was significantly lower than controls in the two patient groups (both p<0.001). The median MTRs (IQR) were 50.5(1.6) percentage units (p.u.) (control), 41.5(10.6) p.u. (CMT1A) and 39.3(8.7) p.u. (CIDP). Moreover, anterior lower leg MTR correlated strongly with strength of ankle dorsiflexion, measured with the Medical Research Council scale, in CIDP (ρ=0.88, p<0.001) and also in CMT1A (ρ=0.50, p<0.05), where MTR also showed an association with disease duration (ρ=−0.86, p<0.001). Short tau inversion recovery MRI of the same muscles showed abnormalities associated with regions of reduced MTR (p<0.001), and MTR was also reduced in other muscles otherwise deemed normal appearing (p<0.001), indicating that MTR may be more sensitive to muscle damaged by denervation than conventional MRI. The significant reductions in muscle MTR in peripheral neuropathies and the associated correlations with clinical measures indicate that MTR has potential as an imaging outcome measure in future therapeutic trials.

MRI shows increased sciatic nerve cross sectional area in inherited and inflammatory neuropathies

Measurements of the cross sectional area of the sciatic nerve are described in a group of 10 patients with genetically confirmed Charcot–Marie–Tooth disease type 1A (CMT1A), nine patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and 10 healthy controls using MRI. One mid-thigh of each individual was imaged using a short tau inversion recovery sequence and the nerve appearance evaluated radiologically with respect to the signal intensity and visibility of the internal neural structure. The cross sectional area of the sciatic nerve of each individual was measured by defining irregular enclosing regions of interest on the MRI images. The sciatic nerve area was enlarged in both CMT1A (p<0.001) and CIDP (p=0.008) compared with controls and in CMT1A compared with CIDP (p<0.001). Median (interquartile range) areas were 67.6 (16.2) mm2 for the CIDP group, 135.9 (46.5) mm2 for the CMT1A group and 43.3 (19.9) mm2 for the control group. The critical upper value for discriminating pathologically enlarged nerves from normal controls with p<0.05 was 64.4 mm2. Quantification of sciatic nerve hypertrophy on MRI may be of assistance in cases where the diagnosis is still in doubt, providing an objective pathological marker complimenting other clinical investigations.

Correcting radiofrequency inhomogeneity effects in skeletal muscle magnetisation transfer maps

The potential of MRI to provide quantitative measures of neuromuscular pathology for use in therapeutic trials is being increasingly recognised. Magnetisation transfer (MT) imaging shows particular promise in this context, being sensitive to pathological changes, particularly in skeletal muscle, where measurements correlate with clinically measured muscle strength. Radiofrequency (RF) transmit field (B1) inhomogeneities can be particularly problematic in measurements of the MT ratio (MTR) and may obscure genuine muscle MTR changes caused by disease. In this work, we evaluate, for muscle imaging applications, a scheme previously proposed for the correction of RF inhomogeneity artefacts in cerebral MTR maps using B1 information acquired in the same session. We demonstrate the theoretical applicability of this scheme to skeletal muscle using a two‐pool model of pulsed quantitative MT. The correction scheme is evaluated practically in MTR imaging of the lower limbs of 28 healthy individuals and in two groups of patients with representative neuromuscular diseases: Charcot–Marie–Tooth disease type 1A and inclusion body myositis. The correction scheme was observed to reduce both the within‐subject and between‐subject variability in the calf and thigh muscles of healthy subjects and patient groups in histogram‐ and region‐of‐interest‐based approaches. This method of correcting for RF inhomogeneity effects in MTR maps using B1 data may markedly improve the sensitivity of MTR mapping indices as measures of pathology in skeletal muscle. Copyright

1700 MRI quantification of lower limb muscle fatty atrophy: a potential outcome measure in chronic neuromuscular diseases

Background Fatty atrophy is a combination of reduced muscle size and the replacement of muscle tissue with fat seen in patients with chronic neuromuscular diseases (NMD). Accurate quantification of fatty atrophy could offer a universal biomarker for trials in chronic NMD. We have assessed its validity as a biomarker by measuring its correlation with muscle strength. Methods We performed 3T MRI including fat quantification by the three-point Dixon method and detailed computerised myometry (CSMi HUMAC NORM) of lower limbs in 18 patients with Charcot-Marie-Tooth-Disease Type 1A (CMT1A), 16 patients with inclusion body myositis (IBM) and 17 healthy volunteers. Regions of interest encompassing whole muscle cross sections were drawn on transverse images at mid-thigh and mid-calf level. The crosssectional area and fat percentage were recorded for each region and used to obtain the ‘remaining muscle area’ (RMA), a measure combining both atrophy and fat replacement. Pearson correlation coefficients between RMA and strength were calculated. Results Excellent correlations were found between RMA and strength for: quadriceps/knee extension (R=0.87), hamstrings/knee flexion (R=0.62), anterior calf muscles/ankle dorsiflexion (R=0.75) and posterior superficial calf muscles/ankle plantarflexion (R=0.68). All correlations were significant p<0.001, including in analyses of the CMT, IBM and volunteer groups separately. Conclusions MRI can quantify fatty atrophy by determining ‘remaining muscle area’. The strong correlation with muscle strength in patients with CMT1A, IBM and healthy volunteers makes it an excellent candidate as an outcome measure in clinical trials of chronic NMD.