Characterizing spinal muscular atrophy with electrical impedance myography.

Electrical impedance myography (EIM) is a non-invasive, painless technique for the evaluation of neuromuscular disease, and here we evaluate its potential application in spinal muscular atrophy (SMA). Twenty-one SMA patients and 18 healthy children underwent EIM of biceps brachii and tibialis anterior using a commercially available impedance device. Hand-held dynamometry and ultrasound assessment of subcutaneous fat thickness were also performed. All EIM parameters differed significantly between both SMA patients and normal subjects and between type 2 and type 3 SMA patients. In addition, EIM had an accuracy level as high as 93% for correctly categorizing patients as type 2 or type 3. Multiple regression analyses confirmed a strong association between EIM and dynamometry. These results confirm that EIM can accurately categorize patients with SMA. Because EIM requires no patient effort and is rapid to apply, it may serve a useful role in future SMA clinical trials.