Blogging Stroke

Fractional Anisotropy Change in Acute Phase of Stroke and its Correlation with Motor Recovery at 3 Months

Qing Hao, MD, PhD

Doughty C, Wang J, Feng W, Hackney D, Pani E, Schlaug G. Detection and Predictive Value of Fractional Anisotropy Changes of the Corticospinal Tract in the Acute Phase of a Stroke. Stroke. 2016

“Doctor, will my father move his right arm again? How much do you think he can recover from this stroke?” As stroke neurologists, we are often asked about the prognosis after the stroke and most time the answer would be, “I am not exactly sure”.

Neuroimaging, especially MRI brain, has been very helpful in prognostication. Previous studies performed on chronic stroke patients demonstrated integrity/ atrophy of cortical spinal tract (CST) and signals indicative Wallerian degeneration (WD) on MRI in the chronic phase closely correlated with motor outcome.

Any neuroimaging markers in the acute phase of stroke can predict motor outcome? CST lesion load (based on initial motor impairment, lesion size and location) and CST integrity still played important roles. When talking about CST integrity, we can’t ignore fractional anisotropy (FA), an imaging marker derived from diffusion tensor imaging, which quantifies the organization (e.g. degree of alignment) and integrity of white matter tracts.

In this article, the author focused on FA in acute phase—they sought to investigate if FA difference in acute phase can be detected and how it predict motor outcome measured by upper extremity Fugl-Meyer score at 3 months.

Retrospective analyses were performed on a prospectively collected cohort of 58 patients with first time ischemic hemispheric stroke. MRI was done within 80 hours after stroke onset. FA values were determined in two regions of interest for 50 patients: cerebral peduncle and a stretch of the CST caudal to each stroke lesion (Nearest-5-Slice – N5S).

The authors were able to detect subtle asymmetry of FA changes (lower FA in the ipsilesional CST), most significantly in the slice that was closest to the ischemic lesion, not in the cerebral peduncle. The slope of the FA laterality index for the nearest-5-slices showed a weak but significant prediction (R²=0.11, p=0,022) for 3-month UE-FM score in univariate analysis, not in multivariate analysis. Not surprisingly, initial UE-FM, weighted CTS lesion load and days of therapy were stronger predictors (R² =0.69, 0.71 and 0.249 respectively, p< 0.001) for 3-months UE-FM score.

CST integrity may be a dynamic change and its predictive value for motor recovery may be different at various stages after stroke. We look forward to more precise prediction models that would help us answer those challenging prognostication questions.