Optical Tool May Allow for Noninvasive Diagnosis of Movement Disorders

Optical Tool May Allow for Noninvasive Diagnosis of Movement Disorders

An innovative technique may help in the diagnosis of muscle impairment and in the treatment of movement disorders, including cerebral palsy, new research shows.

The study, “In Vivo Sarcomere Length Measurement in Whole Muscles during Passive Stretch and Twitch Contractions,” was published in the Biophysical Journal.

In diagnosing and treating muscle disease, the gold standard for direct measurement is an invasive muscle biopsy. However, this procedure can traumatize tissue and cause infection, and it only captures a single time point, dramatically limiting its applicability.

In an attempt to move beyond these limitations, researchers evaluated lower leg muscle function in rabbits during passive stretch and twitch contraction (induced by a single and rapid stimulus), through a technique — called resonant reflection spectroscopy (RRS) — that enabled the simultaneous measurement of 4,200 sarcomeres (the basic units driving contraction of muscle tissue) within less than a millisecond. This key feature may help to develop more accurate and quicker diagnoses.

In RRS, an optical approach enables the calculation of sarcomere length. A laser source illuminates and sweeps across muscle via a fiber-optic probe with a 1/4 mm diameter. The probe collects reflected light from the muscle. This light is then combined and sent to a detector.

RSS is able to detect minimal changes in sarcomere length in response to movement. Moreover, it may enable 3-D reconstruction of sarcomere proteins in the study of muscle diseases.

The technique also offers several advantages in comparison to current approaches like biopsy and endoscopy. Importantly, it presents increased resolution while sampling across a large amount of tissue. It is also minimally invasive and less sensitive to motion artifacts.

RRS may, for these reasons, be a key improvement in clinical assessments of muscle health, and in the long term, it may enable personalized treatment strategies for movement disorders.

Muscle impairment is common in several disorders, including cerebral palsy. RSS “will permit new studies of human muscle function and pathology and permit efficacy testing of muscle treatments,” Richard Lieber, PhD, the study’s lead researcher and a professor at the Rehabilitation Institute of Chicago, said in a press release. “To our knowledge, this method achieves sample sizes, resolutions, and compatibility with human movements that no other current or proposed technique can match.”

Lieber’s group recently applied for a patent on the technique.

“We plan to use this technology in both fundamental and clinical studies of human movement and movement disorders,” Lieber concluded. “We hope that these new experiments lead to better understanding and maintenance of human muscle health.”

The researchers are currently developing a new optical source and probe. Furthermore, they aim to make the technique more affordable to reach widespread clinical use.