Table 1.

Water diffusivity changes found in previous studies by comparing DTI metrics between OSA and control groups

Groups, sex	AHI (events/hr)	Age (yr/old)	FA	MD	RD	AD	Interpretation by the authors
Macey et al. (2008)			↓	n/a	n/a	n/a	Extensive altered white matter diffusion properties in OSA were observed and could potentially reflect damage from hypoxia, oxidative stress, and inflammation.
41 OSA, 7 W Recruited through a sleep disorders laboratory	≥15; 35.7 ± 18.1	46.3 ± 8.9
69 controls, 25 W	n/a	47.5 ± 8.8
Macey, Kumar, Yan‐Go, Woo, and Harper (2012)			↓	n/a	n/a	n/a	An OSA by sex interaction was observed. Women with OSA showed lower FA compared to controls, while this difference was not found in men. This could be representative of different psychological symptomatologies such as depression and anxiety, and/or cardiovascular symptoms in women with OSA specifically.
20 M OSA	≥15; 25.5 ± 2.9	48.9 ± 1.7
10 W OSA Recruited through a sleep disorders laboratory	≥15; 22.5 ± 4.1	52.6 ± 2.4
30 M controls	n/a	49.2 ± 1.4
20 W controls	n/a	50.3 ± 1.7
Kumar et al. (2012)			n/a	↓	n/a	n/a	Reduced global and regional MD with OSA in multiple brain regions suggests acute tissue injury and cytotoxic edema, probably as a result of hypoxia and cardiovascular changes.
23 OSA, 3 W Recruited through a sleep disorders laboratory	≥15; 34.9 ± 24.1	44.4 ± 9.3
23 controls, 3 W	n/a	45.3 ± 11.0
Kumar et al. (2014)			n/a	n/a	↓	↓	Reduced global and widespread regional RD and AD in OSA may indicate acute axonal and myelin injury, respectively, that could be the result of axonal and myelin swelling.
23 OSA, 3 W Recruited through a sleep disorders laboratory	≥15; 34.9 ± 24.1	44.4 ± 9.3
23 controls, 3 W	n/a	45.3 ± 11.0
Castronovo et al. (2014)			↓	↓	n/a	n/a	Before treatment, OSA subjects had lower FA and MD that were concomitant with cognitive impairments, mood alterations, and sleepiness. After 3‐month and 1‐year treatments, a near complete reversal of white matter altered integrity was progressively shown. This reversal was present with recovery to normal levels of cognitive functions.
13 M OSA, before and after 3‐month and 1‐year CPAP treatments	≥30; 61.4 ± 9.8	43.2 ± 7.6
15 M controls	<5; 1.6 ± 1.5	42.2 ± 6.6
Chen et al. (2015)			↓	Ø	↑	Ø	Altered white matter diffusion properties that suggested demyelination in OSA were correlated with leukocyte early apoptosis that is a marker of systemic inflammation.
20 OSA, 2 W Recruited through a sleep center	≥30; 58.9 ± 14.5	38.6 ± 9.9
14 controls, 3 W	<5; 2.9 ± 1.3	38.2 ± 9.9
Lee et al. (2019)			↓	↑	↑	Ø	White matter diffusion properties in OSA suggested reduced axonal number and density and/or altered organization. The tracts with increased FA could account for altered structural brain network properties.
135 OSA, 96 W Recruited in a prospective community‐based cohort	≥5; 12.5 ± 10.0 (76% mild OSA)	59.0 ± 5.9
165 controls, 119 W	<5; 1.9 ± 1.5	58.0 ± 6.0
Koo, Kim, Kim, Seong, and Joo (2019)			↓	↑	n/a	n/a	Localized white matter FA reductions in the uncinate fasciculus correlated with a lower performance to a working memory task, suggesting that white matter alterations may underlie cognitive function in OSA.
38 M OSA Recruited through a sleep clinic	≥30; 56.8 ± 26.2	45.0 ± 6.6
41 M controls	<5; 2.3 ± 2.2	37.2 ± 10.7
(B. Zhang et al., 2019) 20 OSA, 16W			↓	↑	↑	Ø	The authors investigated white matter microstructure of the corpus callosum, and found that in the anterior corpus callosum, alterations were associated with worse prospective memory and sustained attention in OSA.
Recruited through a sleep disorders hospital	≥15; 49.0 ± 22.5	43.1 ± 10.5
24 controls, 15W	n/a	40.7 ± 10.0

Abbreviations: AD, axial diffusivity; AHI, apnea–hypopnea index; CPAP, continuous positive airway pressure treatment; DTI, diffusion tensor imaging; FA, fractional anisotropy; MD, mean diffusivity; M, men; OSA, obstructive sleep apnea; n/a, nonapplicable or nonavailable; RD, radial diffusivity; W, women; Ø, no between‐group differences.