Utility of transorbital ultrasound to assess disability and axonal loss in multiple sclerosis

In multiple sclerosis (MS), axonal damage plays a significant role in contributing to disability. This study assesses the diagnostic accuracy and use of transorbital sonography (TOS) as a surrogate for axonal loss by measuring the optic nerve diameter (OND) and optic nerve sheath diameter (ONSD).

It was a cross-sectional study in the Neurology Department, Government Medical College, Thiruvananthapuram. MS patients were enrolled, and expanded disability status scale (EDSS) scores assessed their disability. Disability was defined as EDSS > 2. OND and ONSD were measured using TOS. The retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) were measured using optical coherence tomography (OCT). We constructed receiver operating characteristics curve using RNFL as gold standard to detect axonal loss and disability. The sensitivity and specificity of GCC, OND and ONSD were independently calculated from the ROC curve which could predict the disability.

The EDSS scores varied from 0 to 5.5. The disabled group had 10.3 ± 1.9 μm thinner RNFL (p < 0.001), 40.8 ± 15.5 μm thinner GCC (p 0.0038) as compared to the nondisabled group. OND was 3.8 ± 0.6 mm thinner (p 0.037) and ONSD was 4.6 ± 0.6 mm thinner (p 0.010) as compared to the control group. OND and RNFL were independent predictors for disability; the optimum cut-off to detect disability was 4.35mmfor OND and 12 μm for RNFL; the optimum cut-off to detect axonal loss was 4.43 mm for OND.

We found an optimum OND and RNFL cutoff to predict disability and an optimum cut-off for OND to predict axonal loss. TOS could be an economical and accurate alternative to OCT.