Tongue fat and its relationship to obstructive sleep apnea

Abstract

Study objectives: The objective of this study was to determine whether tongue fat is increased in obese sleep apneics compared to obese subjects without sleep apnea. We hypothesized that excess fat is deposited in the tongue in obese patients with sleep apnea.

Design: Case-control design.

Setting: Academic medical center.

Patients: We examined tongue fat in 31 obese controls (apnea-hypopnea index, 4.1 ± 2.7 events/h) and 90 obese apneics (apnea-hypopnea index, 43.2 ± 27.3 events/h). Analyses were repeated in a subsample of 18 gender-, race-, age-, and BMI-matched case-control pairs.

Interventions: All subjects underwent a MRI with three-point Dixon magnetic resonance imaging. We used sophisticated volumetric reconstruction algorithms to study the size and distribution of upper airway fat deposits in the tongue and masseter muscles within apneics and obese controls.

Measurements and results: The data supported our a priori hypotheses that after adjustment for age, BMI, gender, and race, the tongue in apneics was significantly larger (P = 0.001) and had an increased amount of fat (P = 0.002) compared to controls. Similar results were seen in our matched sample. Our data also demonstrate that within the apneic and normal tongue, there are regional differences in fat distribution, with larger fat deposits at the base of the tongue.

Conclusions: There is increased tongue volume and deposition of fat at the base of tongue in apneics compared to controls. Increased tongue fat may begin to explain the relationship between obesity and obstructive sleep apnea.

Keywords: obstructive sleep apnea; tongue fat.

Figure 1

Comparison of tongue fat using standard T1-weighted spin echo MR imaging vs. fat-weighted Dixon MR imaging sequences in an apneic patient. Anatomic definitions of the upper airway regions are demonstrated: retropalatal (RP)—from level of hard palate to caudal margin of soft palate; and retroglossal (RG)—from caudal margin of soft palate to base of tongue. Soft palate, tongue, tongue fat, and airway are denoted with arrows. Both sagittal images are mid-sagittal and axial images are shown at same level of (mid) tongue. Note that fat deposits in tongue are more easily visualized using Dixon MR imaging sequence than the spin echo sequence.

Figure 2

Representative three-dimensional volumetric reconstruction of tongue (red) and fat within tongue (yellow) from series of 3-mm contiguous axial MR images superimposed on a midsagittal image; 8 sections of apneic tongue (red) including tongue fat (yellow), 4 within RP (retropalatal) region and 4 within RG (retroglossal) region of tongue. There is substantially more fat at base of tongue.

Figure 3

The mean and 95% confidence intervals for our primary outcomes of interest are shown for cases and controls, both in our overall sample and for the age, BMI, gender, and race-matched pairs. * After adjustment for age, BMI, gender, and race, we observe significant differences between cases and controls for tongue volume and tongue fat, both in the overall population (P = 0.001 and P = 0.002, respectively) and in our matched sample (P = 0.022 and P = 0.010, respectively). There were no significant differences in masseter fat between the apneics and controls. In all subjects tongue fat % is greater than masseter fat %.

Figure 4

Representative three-dimensional volumetric reconstructions of tongue (red) and fat within tongue (yellow) from series of 3-mm contiguous axial MR images superimposed on midsagittal images in BMI-matched post-menopausal female patient with OSA (left) and post-menopausal female control subject (right) (subjects also matched for age and ethnicity). The apneic tongue is much larger and there is increased tongue fat deposition throughout the apneic tongue.

Figure 5

Graphical box and whisker plot comparison of tongue fat distribution within apneics and controls. The gray box represents the interquartile range (IQR = 75^th Percentile – 25^th Percentile), with the black line within the box showing the median value. The “whiskers” extend from the box either to the respective minimum or maximum value, or 1.5 × IQR from the 25^th and 75^th percentiles if points lie outside this range. After adjustment for age, gender, BMI, and race, the percentage of intramuscular fat in the lower mid RG (P = 0.003) and lower RG (P < 0.001) regions of tongue is significantly greater in apneics than in controls. RP = retropalatal and RG = retroglossal.