The Rectus Femoris Central Tendon Sign: An Ultrasound Surrogate Marker of Function in Spinal and Bulbar Muscular Atrophy


Clinical Trials

Poster Number: T396


Abdullah AlQahtani, MD, MPH, National Institutes of Health, Angela Kokkinis,, BSN, RN, NIH, Mina Jain, PT, DSc, NIH, Galen Joe, MD, National Institutes of Health, Tianxia Wu, MD, NIH, Katharine Alter, MD, National Institutes of Health, Christopher Grunseich, MD, Neuromuscular and Neurogenetic Disorders of Childhood Section, NINDS, NIH

Background: Patient friendly cost-effective makers of functional status in SBMA are important for patients, physicians, and researchers. The use of neuromuscular ultrasound is expanding both in the clinical and research settings. Some SBMA patients have no visible central tendon on ultrasound scans of their RF. This is due to obscuration from increased muscle echogenicity representing fatty replacement and fibrosis. We hypothesized that those with an obscured tendon are functionally weaker.

Objective: Describe and validate a a novel clinical neuromuscular ultrasound marker that predicts functional status in spinal bulbar muscular atrophy.

Design and methods Participants were enrolled in an IRB approved observational natural history study of SBMA at the National Institutes of Health. Clinical ultrasound was performed by two investigators who independently labeled the presence or absence of the rectus femoris (RF) central tendon on transverse images of the RF. Functional measures were performed by investigators who were not involved in other analysis. for validation, we selected all available standardized and validated functional assessment tools as primary outcome measures (spinal and bulbar muscular atrophy functional rating scale-lower limb, 6-minute walk test, quantitative muscle assessment, and adult myopathy assessment tool.

Results: 14 ambulatory patients were enrolled with a mean age of 60. Eight patients had a visible tendon. All p-values were two-tailed and the statistical significance level was set at 0.0125. The association of RF tendon status to all 4 primary outcome measurers showed a P value of <0.0001. The results remained significant after adjusting for confounding factors including disease duration and BMI. Conclusion: The study confirms the obscured rectus femoris tendon (ORFT) sign as a novel marker of functional status in SBMA. It is a simple tool that can be used by both clinicians and researchers.