Brain putamen volume changes in newly-diagnosed patients with obstructive sleep apnea

Abstract

Obstructive sleep apnea (OSA) is accompanied by cognitive, motor, autonomic, learning, and affective abnormalities. The putamen serves several of these functions, especially motor and autonomic behaviors, but whether global and specific sub-regions of that structure are damaged is unclear. We assessed global and regional putamen volumes in 43 recently-diagnosed, treatment-naïve OSA (age, 46.4 ± 8.8 years; 31 male) and 61 control subjects (47.6 ± 8.8 years; 39 male) using high-resolution T1-weighted images collected with a 3.0-Tesla MRI scanner. Global putamen volumes were calculated, and group differences evaluated with independent samples t-tests, as well as with analysis of covariance (covariates; age, gender, and total intracranial volume). Regional differences between groups were visualized with 3D surface morphometry-based group ratio maps. OSA subjects showed significantly higher global putamen volumes, relative to controls. Regional analyses showed putamen areas with increased and decreased tissue volumes in OSA relative to control subjects, including increases in caudal, mid-dorsal, mid-ventral portions, and ventral regions, while areas with decreased volumes appeared in rostral, mid-dorsal, medial-caudal, and mid-ventral sites. Global putamen volumes were significantly higher in the OSA subjects, but local sites showed both higher and lower volumes. The appearance of localized volume alterations points to differential hypoxic or perfusion action on glia and other tissues within the structure, and may reflect a stage in progression of injury in these newly-diagnosed patients toward the overall volume loss found in patients with chronic OSA. The regional changes may underlie some of the specific deficits in motor, autonomic, and neuropsychologic functions in OSA.

Keywords: 3D surface morphometry; 3D, Three dimensional; AHI, Apnea–hypopnea index; Autonomic; BAI, Beck Anxiety Inventory; BDI-II, Beck Depression Inventory II; Basal ganglia; CSF, Cerebrospinal fluid; Cognition; ESS, Epworth Sleepiness Scale; FA, Flip angle; FOV, Field of view; GRAPPA, Generalized autocalibrating partially parallel acquisition; Intermittent hypoxia; MNI, Montreal Neurological Institute; MPRAGE, Magnetization prepared rapid acquisition gradient-echo; MRI, Magnetic resonance imaging; Magnetic resonance imaging; Motor; OSA, Obstructive sleep apnea; PD, Proton density; PSQI, Pittsburgh Sleep Quality Index; TE, Echo time; TIV, Total intracranial volume; TR, Repetition time.

Fig. 1

Global putamen volumes of OSA and control subjects. Both left and right putamen volumes were significantly increased in recently-diagnosed, treatment naïve OSA over control subjects, controlling for age, gender, and TIV (left, p = 0.043; right, p = 0.027).

Fig. 2

Areas of regional putamen volume increase and decrease in OSA compared to control subjects, with areas shown from a dorsal perspective (Left), and a ventral perspective (Right). The color coding represents ratios of radial distance of each surface point from control reference values, with warm colors (orange to red) indicating volume losses and cool colors (blue to purple) representing volume increases; those corresponding sites are labeled with letters (a–q). Bilateral sites with increased putamen volume in the OSA group included mid and caudal-ventral portions, based on OSA to control group ratios, and decreased volumes emerged in bilateral rostral and mid-dorsal regions, extending to ventral areas (a–q).