Craig M. Zaidman

Introduction: Electrical impedance myography (EIM) is a non‐invasive, painless, objective technique to quantify muscle pathology. Methods: We measured EIM in 8 arm and leg muscles in 61 boys with Duchenne muscular dystrophy (DMD) and 31 healthy boys, ages 3–12 years, at 5 centers. We determined the reliability of EIM and compared results in boys with DMD to controls and to 6‐minute walk distance (6MWD), North Star Ambulatory Assessment (NSAA), timed functional tests (TFTs), and strength (hand‐held dynamometry). Results: EIM was well tolerated and had good inter‐ and intrarater reliability (intraclass correlation coefficient 0.81–0.96). The averaged EIM phase value from all muscles was higher (P < 0.001) in controls (10.45 ± 2.29) than boys with DMD (7.31 ± 2.23), and correlated (P ≤ 0.001) with 6MWD (r = 0.55), NSAA (r = 0.66), TFTs (r = –0.56), and strength (r = 0.44). Conclusion: EIM is a reliable and valid measure of disease severity in DMD. Longitudinal studies comparing EIM with other assessments over time in DMD are warranted. Muscle Nerve 52: 592–597, 2015

Introduction: The radial nerve and posterior interosseous nerve (PIN) are prone to injury at multiple sites. Electrodiagnostic (EDx) studies may only identify the most proximal lesion. Nerve ultrasound could augment EDx by visualizing additional pathology. Methods: This investigation was a retrospective examination of ultrasound and EDx from 26 patients evaluated for posterior cord/radial/PIN lesions. Results: Eighteen of 26 patients had abnormalities on EDx (15 radial, 2 PIN, 1 posterior cord). Ultrasound identified 15 of 18 (83%) of the EDx abnormalities and provided additional diagnostic information. In 6 of 15 (40%) patients with EDx evidence of radial neuropathy, ultrasound identified both radial nerve enlargement and additional, unsuspected PIN enlargement (53% to 339% enlarged vs. unaffected side). Ultrasound also identified: nerve (dis)continuity at the trauma site (n = 8); and nerve tumor (n = 2; 1 with normal EDx). Conclusion: In radial neuropathy, ultrasound often augments EDx studies and identifies a second lesion in the PIN. Further studies are required to determine the etiology and significance of this additional distal pathology. Muscle Nerve 53: 379–383, 2016

Introduction: Quantitative muscle ultrasound (QUS) in boys with Duchenne muscular dystrophy (DMD) shows increased echointensity as muscle is replaced with fat and fibrosis. Studies of quantitative ultrasound in infants/young boys with DMD over time have not been reported. Methods: We used calibrated muscle backscatter (cMB), a reproducible measure of ultrasound echointensity, to quantify muscle pathology in 5 young boys with DMD (ages 0.5–2.8 years) over 17–29 months. We compared the results with repeated assessments of function (n = 4) and with muscle ultrasound images from a cross‐section of 6 male controls (0.6–3.1 years). Results: cMB in boys with DMD increased (worsened) over time (P < 0.001), whereas function improved. After age 2 years, cMB in most (4 of 5) boys with DMD was higher than in any control. Conclusions: QUS measures disease progression in young boys with DMD despite functional improvements. QUS could be employed as an outcome measure for serial assessment of young boys with DMD. Muscle Nerve 52: 334–338, 2015

Introduction: Muscle pathology in Duchenne muscular dystrophy (DMD) can be quantified using ultrasound by measuring either the amplitudes of sound‐waves scattered back from the tissue [quantitative backscatter analysis (QBA)] or by measuring these backscattered amplitudes after compression into grayscale levels (GSL) obtained from the images. Methods: We measured and compared QBA and GSL from 6 muscles of 25 boys with DMD and 25 healthy subjects, aged 2‐14 years, with age and, in DMD, with function (North Star Ambulatory Assessment). Results: Both QBA and GSL were measured reliably (intraclass correlation ≥ 0.87) and were higher in DMD than controls (P < 0.0001). In DMD, average QBA and GSL measured from superficial regions of muscle increased (rho ≥ 0.47, P < 0.05) with both higher age and worse function; in contrast, GSL measured from whole regions of muscle did not. Conclusions: QBA and GSL measured from superficial regions of muscle can similarly quantify muscle pathology in DMD. Muscle Nerve 51: 207–213, 2015

Introduction: Nerves are often enlarged in chronic inflammatory demyelinating polyneuropathy (CIDP). In this investigation we studied changes with treatment over time. Methods: We retrospectively compared serial ultrasound measurements of median and ulnar nerve size with clinical and electrodiagnostic evaluations in 23 CIDP subjects. We defined remission as stable clinical improvement on low or decreasing amounts of medication. Results: Nerves were normal at last follow‐up more often in subjects who achieved remission than in those who did not (10 of 13 vs. 0 of 10, P = 0.0001). Nerves were normal or smaller (>30% reduction) more often in subjects whose grip strength improved or remained strong compared those whose grip strength weakened (12 of 16 vs. 0 of 3, P = 0.04), and in subjects whose demyelinating electrodiagnostic features resolved compared with those whose demyelination persisted (7 of 7 vs. 6 of 12, P = 0.04). Over time, nerve size decreased more in subjects with baseline nerve enlargement who achieved remission than in those who did not (−41% vs. 7%, P = 0.04). Conclusion: In CIDP, enlarged nerves normalized or decreased with remission. Muscle Nerve 50: 733–738, 2014

Introduction: Quantitative ultrasound can measure skeletal muscle pathology. We investigated whether inexperienced evaluators could accurately obtain and analyze ultrasound images. Methods: Two examiners underwent a 20‐minute training session before obtaining ultrasound images of several limb muscles in 21 healthy boys and 19 boys with Duchenne muscular dystrophy (DMD). Gray scale levels (GSLs) of muscle and subcutaneous fat were then measured by 2 analysts: a trained research assistant and a radiologist. We compared results between examiners and analysts. Results: Interrater reliability of muscle GSLs was high between examiners (ICC ≥ 0.85) and analysts (ICC ≥ 0.84). As anticipated, GSLs were higher in dystrophic than in healthy muscles (P < 0.001). Fat GSLs were less reliable (ICC = 0.5–0.89) than muscle and increased with age and body size. Conclusions: GSLs from ultrasound images of healthy and dystrophic skeletal muscle, but not from subcutaneous fat, can be obtained reliably and can be analyzed by inexperienced evaluators with minimal training. Muscle Nerve 50: 124–128, 2014

We compared features of nerve enlargement in inherited and acquired demyelinating neuropathies using ultrasound. We measured median and ulnar nerve cross-sectional areas in proximal and distal regions in 128 children and adults with inherited [Charcot–Marie–Tooth-1 (CMT-1) (n = 35)] and acquired [chronic inflammatory demyelinating polyneuropathy (CIDP) (n = 55), Guillaine–Barre syndrome (GBS) (n = 21) and multifocal motor neuropathy (MMN) (n = 17)] demyelinating neuropathies. We classified nerve enlargement by degree and number of regions affected. We defined patterns of nerve enlargement as: none, no enlargement; mild, nerves enlarged but never more than twice normal; regional, nerves normal in at least one region and enlarged more than twice normal in at least one region; diffuse, nerves enlarged at all four regions with at least one region more than twice normal size. Nerve enlargement was commonly diffuse (89 %) and generally more than twice normal size in CMT-1, but not (p < 0.001) in acquired disorders which mostly had either no, mild or regional nerve enlargement [CIDP (64 %), GBS (95 %), and MMN (100 %)]. In CIDP, subjects treated within 3 months of disease onset had less nerve enlargement than those treated later. Ultrasound identified patterns of diffuse nerve enlargement can be used to screen patients suspected of having CMT-1. Normal, mildly, or regionally enlarged nerves in demyelinating polyneuropathy suggests an acquired etiology. Early treatment in CIDP may impede nerve enlargement.