Skewness of Fractional Anisotropy Detects Decreased White Matter Integrity Resulting From Acute Optic Neuritis.

PURPOSE: Diffusion tensor imaging (DTI) has demonstrated optic nerve damage associated with optic neuritis (ON); however, the usefulness of mean fractional anisotropy (FA) specifically is varied in the literature. We wished to determine whether histogram analysis of FA better detects ON damage than mean FA.

METHODS

The ON patients (n = 24) underwent DTI within 1 month of symptoms and then 6 months later (n = 21). Twelve control subjects participated in one session. Mean FA and axial (AD), radial (RD), and mean (MD) diffusivities were compared between ON and fellow eyes, control eyes, and sessions. Values were sorted into bins, and coefficients of skewness of FA, AD, RD, and MD were compared between ON and fellow eyes, control eyes, and sessions.

RESULTS

Mean AD, RD, and MD of ON eyes were significantly reduced compared with fellow eyes (P < 0.04) within 1 month of symptoms, but did not differ at 6 months. Mean AD and RD of ON eyes were significantly lower than control eyes (P < 0.05). No differences were observed for mean FA. The coefficient of skewness of FA was significantly different between ON eyes and fellow eyes (P = 0.03) and control eyes (P = 0.04) within 1 month of symptoms, but did not differ at 6 months. No differences were observed for AD, RD, and MD.

CONCLUSIONS

Skewness of FA can detect white matter damage associated with ON and its recovery, which may further inform us of how DTI can measure white matter injury and repair.