Science News: An Appraisal of Electrodiagnostic Studies in Stiff Person Syndrome

Submitted by: Betul Gundogdu, MD
Edited by: Niranjan Singh, MD

Li Y, Thakore N. An appraisal of electrodiagnostic studies in stiff person syndrome. J Clin Neuromuscul Dis. 2020;22(2):84-89. doi:10.1097/CND.0000000000000302

Summary: This is a review of electrodiagnostic (EDX) findings for diagnosis of stiff person syndrome (SPS). The authors performed a literature review of EDX findings in SPS as well as an online survey on the use of EDX testing for the evaluation of SPS among EDX laboratory test results accredited by the EDX Laboratory Accreditation Committee of the American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM). Additionally, they studied the simultaneous motor unit firing in selected groups of agonist and antagonist muscles among a small group of healthy subjects.

Literature review suggested that exteroceptive reflex testing on NCS and searching for continuous muscle unit activation (CMUA) or simultaneous agonist-antagonist activation on EMG are the most informative EDX techniques for SPS. Exteroceptive reflex recording can be performed in proximal and distal muscles of the extremities (biceps, triceps, abductor pollicis brevis, quadriceps, biceps femoris, tibialis anterior) as well as axial muscles. However, survey result indicated that exteroceptive reflex testing is rarely used by AANEM accredited EDX laboratories. CMUA studies was mostly performed in thoracolumbar paraspinal or abdominal muscles. The authors also demonstrated that simultaneous voluntary coactivation of selected agonist and antagonist muscle groups (biceps-triceps, rectus femoris-semitendinosus, tibialis anterior-soleus) can be observed on EMG in healthy subjects.

In conclusion, positive EDX findings may serve as supportive evidence but has limitations in confirming the diagnosis SPS.

Comments: This article clarifies that based on the current evidence, EDX studies alone are not sufficient for a diagnosis of SPS. Further studies may be conducted to explore the utility of exteroceptive reflex testing and CMUA in patients with suspected SPS, other forms of movement disorders as well as healthy subjects. Based on this information, electromyographers can modify their approach to suspected SPS patients.