Diffusion tensor imaging metrics in diagnosis of HTLV-1-associated myelopathy

Abstract

Objective: In the diagnosis of HTLV-1-associated myelopathy (HAM), while magnetic resonance imaging (MRI) is essential to exclude other diseases, its power is limited regarding HAM diagnosis, as only 30% of affected patients present with spinal cord atrophy. Diffusion tensor imaging (DTI) may enable the detection of damage in the white matter microstructure. Here, we quantitatively assess spinal cord damage using DTI and evaluate conventional MRI parameters of the spinal cord in HTLV-1-infected individuals.

Methods: This cross-sectional study involved 33 HTLV-1 carriers, 28 patients with definite-HAM, and 11 seronegative healthy subjects (HS). Region-of-interest (ROI)-based fractional anisotropy (FA) and mean diffusivity (MD) measurements were performed in the upper thoracic and lumbar regions of the spinal cord. Thoracic index was defined as 1/ (anteroposterior diameter × transverse diameter) measured at the fifth 5th vertebral level. Receiver operating characteristic (ROC) curve analysis was used to determine optimal cutoff FA, MD, and thoracic index values.

Results: Spinal cord atrophy was observed in 15 (53.6%) patients with definite-HAM. The area under the ROC curve in the thoracic spinal cord was 0.824 (95% CI, 0.716-0.932), 0.839 (95% CI: 0.736-0.942), and 0.838 (95% CI: 0.728-0.949) for FA, MD, and the thoracic index, respectively. Lower FA and higher MD values were observed in the definite-HAM group compared to HTLV-1 carriers and HS at the T5 vertebral level (p < 0.01).

Interpretation: Complementary to conventional MRI, DTI analysis of the spinal cord and thoracic index determination can offer additional insight that may prove useful in the diagnosis of HAM.

Figure 1

Region‐of‐interest (ROI) placement. Placement of the measurement ROIs on the axial B0 image at the 5th thoracic vertebral level (A) and the lower cord immediately above the conus medullaris (B).

Figure 2

ROC curve analysis of fractional anisotropy (FA), mean diffusivity (MD), and thoracic index (TI) values in 31 asymptomatic HTLV‐1 carriers and 26 HAM patients at the T5 vertebral level. MD: area under the curve: 0.839 (95% CI: 0.736–0.942), optimal cutoff: 1.3445, with 74.2% sensitivity and 84.6% specificity at cutoff. FA: area under the curve: 0.824 (95% CI: 0.716–0.932), optimal cutoff 0.545, 83.9% sensitivity, and 73.1% specificity at cutoff. TI: area under the curve: 0.838 (95% CI: 0.728–0.949), optimal cutoff 2.48, 84.4% sensitivity and 80.8% specificity at cutoff.