EIM effective as a diagnosis tool for SMA

Electrical impedance myography (EIM), an electrophysiologic technique used for assessing muscular health by measuring physical parameters such as resistance in response to applied electrical current, provides clinically relevant information in patients with spinal muscular atrophy, researchers stated here at the American Neurological Association 134th Annual Meeting.
"Although still under refinement, the technique offers the promise of a useful, noninvasive method of neuromuscular disease evaluation," said Seward Brian Rutkove, MD, Department of Neurology, Beth Israel Deaconess Medical Center and Children's Hospital, Harvard Medical School, Boston, Massachusetts.
"One application for which EIM may be especially well-suited is the monitoring of muscle condition in children with SMA," hence addressing a need to effectively assess disease burden, especially in children with type 2 or 3 SMA, he added.

In diseased muscle, EIM parameters such as tissue resistance, capacitance, and phase differ from those in healthy muscle: upon applying electrical current, the resistance increases and the capacitance decreases, causing the measured voltage to have a lower amplitude and, hence, to be less out-of-phase with the applied current, explained Dr. Rutkove.
The investigators aimed to evaluate whether EIM can discriminate between disease type. "The fact that type 2 SMA patients can be effectively distinguished from type 3 supports the hypothesis that patients with more severe disease have more abnormal EIM spectra," Dr. Rutkove remarked.
The study enrolled 21 patients with genetically confirmed type 2 and type 3 SMA and 18 health controls. Biceps and tibialis anterior on the dominant side were studied in all study participants, using EIM, ultrasound, and handheld dynamometry.
Data acquired indicate that EIM could differentiate between type 2 and type 3 SMA patients with high accuracy.

(source: Docguide)