lists alcohol consumption measures and other demographic and clinical variables. All groups were equivalent on age [F(2,55) = 0.83, P = 0.44] but not on education [F(2,55) = 12.1, P = 0.001], with nsLDs having more education than both nsADIs and sADIs (both P < 0.003). nsADIs and sADIs consumed a similar average number of alcoholic drinks per month over 1 and 3 years prior to enrolment (P > 0.48). However, nsADIs began drinking at heavy levels (i.e. >100 drinks/month) at older age (30.4 ± 11.7 versus 19.5 ± 3.5, P = 0.001) and had fewer drinks per month over lifetime than sADIs (162 ± 86 versus 271 ± 168, P = 0.02). nsADIs did not differ from sADIs on self-reported measures of depressive, anxiety and withdrawal symptomatology, haemoglobin, haematocrit and red blood cell counts (all P > 0.34). In both alcohol-dependent individual groups, the liver enzymes γ-glutamyltransferase and aspartate-aminotransferase levels were elevated at baseline but normalized before follow-up, whereas their red blood cell counts were below normal at both assessments. Pre-albumin was within normal range for both nsADIs and sADIs, suggesting no gross malnourishment.
Demographics, alcohol consumption and clinical variables (mean ± SD)
The sADI Fagerstrom score was 5.2 ± 2.2, indicating medium to high levels of nicotine dependence. The sADI participants smoked on an average 20.6 ± 11.6 cigarettes per day for 20.8 ± 12.4 years, resulting in 24 ± 22 pack-years. Most nsADIs were overweight or obese (BMI > 25), whereas sADIs were generally at normal weight or overweight (20 < BMI < 30; ). These group characteristics were similar in the smaller cohort used for longitudinal analyses.
According to a clinical neuroradiologist’s review of study MRI, five nsADIs (31%) and nine sADIs (45%) demonstrated white matter signal hyperintensity (χ2 = 0.71, P = 0.40). Specifically, three nsADIs and two sADIs had punctate foci, two nsADIs and four sADIs had early confluence of white matter signal hyperintensities, and three sADIs (but no nsADIs) had large confluent areas of white matter signal hyperintensities. The presence of these white matter signal hyperintensities did not affect our DTI results as they segmented as grey matter or CSF, and thus, did not contribute to our white matter MD and FA measures. The smaller sample used in longitudinal analyses had demographics, clinical indices and white matter signal hyperintensity distribution similar to the larger cross-sectional cohort at baseline.
Cross-sectional group comparisons at baseline
This analysis tested the first hypothesis that MD is highest and FA is lowest in sADIs, followed by nsADIs and nsLDs.
Comparison of frontal white matter MD using Generalized Linear Model indicated significant group differences [χ2(2) = 10.45, P = 0.03]. Follow-up group comparisons revealed that nsADIs had 3.9% higher (P = 0.005, ES = 0.96) and sADIs 2% higher (P = 0.05, ES = 0.62) frontal white matter MD than nsLDs, with a trend for 1.9% higher MD in nsADIs than in sADIs (P = 0.10, ES = 0.44). Among the hypothesized group differences, nsADIs demonstrated higher MD than nsLDs in the temporal (3.1%, P = 0.005, ES = 0.88) and parietal lobes (3.3%, P = 0.003, ES = 0.96), but sADIs were not significantly different from nsLDs (ES < 0.4). No group differences were apparent for any of the lobar FA measures (P > 0.20); the effect sizes were consistently larger for comparisons between nsADIs and nsLDs than for comparisons between sADIs and nsLDs, consistent with MD results.
Lobar white matter volumes were insignificantly different between the three groups (<3%, P > 0.09, ES < 0.3). Among metabolites and after using age and BMI as covariates, the MANCOVA comparing NAA between groups was marginally significant [F(8,80) = 1.81, P = 0.09]. However, among the hypothesized contrasts, NAA was 9% lower in frontal white matter of sADIs than in nsLDs (P = 0.03, ES = 0.85) and 10% lower in parietal white matter of nsADIs as compared with nsLDs (P = 0.05, ES = 0.87), with a trend for 8% lower NAA in parietal white matter of sADIs relative to nsLDs (P = 0.08, ES = 0.71). Also, lobar white matter Cho, creatine and m-inositol concentrations did not differ significantly between groups (all P > 0.44, ES < 0.35).
Finally, all the differences between nsADIs and sADIs reported above were not explained by group differences in alcohol consumption. Furthermore, the results reported in this paragraph were not appreciably affected by excluding participants with co-morbid depressive disorders, cardiovascular disease or history of drug abuse/dependence. Same patterns of group differences were observed within the subsample re-scanned at follow-up.
Changes over 1 month of abstinence from alcohol
This analysis tested the second hypothesis that reductions of MD and increases in FA, volumes and increases in concentrations of NAA and Cho with abstinence from alcohol will be more pronounced in nsADIs than in sADIs. The results are depicted in .
Figure 3 Patterns of longitudinal frontal white matter changes in (A) MD, (B) FA, (C) volume and (D) NAA concentration observed in participants who were scanned at baseline and follow-up: the P-values pertain to longitudinal changes. Please, note the significant (more ...)
The omnibus dMANOVA comparing lobar FA in nsADIs and sADIs between baseline and follow-up demonstrated a significant effect for time [F(4,16) = 4.04, P = 0.019] and a trend for an interaction between smoking status and time [F(4,16) = 2.43, P = 0.09]. The follow-up ANOVAs demonstrated a significant effect for time [F(1,19) = 12.9, P = 0.002] and an interaction between smoking status and time [F(1,19) = 10.57, P = 0.004] in temporal white matter. These findings appeared to be driven by significant increases in temporal white matter FA of nsADIs (3.5 ± 2.6%, P = 0.003). nsADIs also showed a trend for increasing FA in the frontal white matter (1.5 ± 3.0%; P = 0.06), whereas sADIs demonstrated no FA changes over the same interval (P > 0.16, per cent changes <0.57%). Covariation for group differences in total lifetime consumption of ethanol did not appreciably alter these findings.
dMANOVA yielded no main effects or interactions for smoking status or time. Although the follow-up repeated measures ANOVAs pointed to some effects for time and/or time by smoking status interactions, they were not significant after correction for multiple comparisons. Importantly and consistent with FA changes, only nsADIs demonstrated a pattern of MD decrease in white matter of frontal (−1.5 ± 2.3%, P = 0.04, uncorrected), temporal (−1.8 ± 2.0%, P = 0.01, uncorrected), parietal (−1.8 ± 2.3%, P = 0.02, uncorrected) and occipital lobes (−2.6 ± 4.0%, P = 0.03, uncorrected). No corresponding changes over the same interval were observed among sADIs (P > 0.16, uncorrected, per cent changes <0.34%). Covariation for group differences in total lifetime consumption of ethanol did not appreciably alter these patterns.
The omnibus dMANOVA yielded a significant interaction between smoking status and time [F(4,15) = 3.05, P = 0.05]. This result reflected pattern of volume increases in frontal (1.2 ± 1.5%, P = 0.01, uncorrected) and temporal white matter (1.5 ± 2.1%, P = 0.03, uncorrected) of sADIs, with no patterns of volume changes in nsADIs (P > 0.27, uncorrected, percent change <0.5%). Finally, we have obtained similar patterns using monthly rates of changes. This assures that the observed differences in recovery between nsADIs and sADIs are not a consequence of the numerically larger inter-scan interval in nsADIs (37.5 days) compared with sADIs (31.2 days).
dMANOVAs for NAA, Cho and m-inositol concentrations did not yield any significant effects of time (P > 0.27) or time by smoking status interactions (P > 0.55).
Finally, additional comparisons indicated that none of the above results were appreciably influenced by participants with co-morbid conditions.
Cross-sectional group differences at 5-week follow-up
In the smaller longitudinal sample of 21 sADIs and nsADIs, the group differences between nsADIs and sADIs at 5-week follow-up and nsLDs re-scanned after 1 year did not reach statistical significance for lobar white matter MD and FA, lobar white matter volumes or mean lobar metabolite concentrations [all F(8,46) < 1.57, all P > 0.23], possibly due to normalization of magnetic resonance measures and/or low statistical power.
Relationships between outcome measures at baseline
We tested the hypotheses that in alcohol-dependent individuals (nsADIs and sADIs combined) at 1 week of abstinence (baseline) higher lobar MD is associated with lower FA, smaller white matter volumes and lower concentrations of NAA within the same white matter regions.
At baseline, larger white matter volumes were moderately related to lower MD and higher FA, but these associations did not survive corrections for multiple comparisons. Greater age in alcohol-dependent individuals was associated with higher MD in all regions (0.40 < r < 0.57, P < 0.03) and lower FA in frontal and temporal white matter (r < −0.46, P < 0.01). After correction for age, higher FA was associated with lower MD in total white matter and all lobar regions (r < −0.70, P < 0.004); smoking status did not affect these relationships. These patterns remained significant when participants with co-morbid mood disorders, hypertension or white matter lesions were excluded from analyses. In addition, when participants with co-morbid mood disorders only were excluded, we observed a positive statistical association between frontal white matter volume and frontal NAA concentration (r = 0.66, P = 0.008). Finally, a higher amount of alcohol consumed over lifetime (in kilograms) was associated with higher MD (r = 0.29, P = 0.04) and lower FA (r = −0.34, P = 0.02) in total white matter, and surprisingly, later onset of heavy drinking was associated with higher total white matter MD (r = 0.35, P = 0.02). Otherwise, the FA and MD measures in alcohol-dependent individuals were not related to the average numbers of drinks per month over 1, 3 and 8 years, prior to enrolment or with any measures of smoking severity in sADIs.
Relationships between outcome measures changes over 1 month of abstinence from alcohol
We hypothesized that over 1 month of abstinence from alcohol, decreasing lobar white matter MD is associated with corresponding increases in FA, white matter volumes and NAA concentrations, whereas increasing Cho is associated with increasing white matter volumes in the same regions.
Over the month of abstinence from alcohol and within alcohol-dependent individuals, the MD decreases were associated with FA increase in total white matter (r = −0.44, P = 0.02) and among lobes in frontal (r = −0.56, P = 0.016), temporal (r = −0.49, P = 0.048) and occipital white matter (r = −0.53, P = 0.024), supporting our hypothesis. There were no patterns of associations between longitudinal changes of markers obtained with different magnetic resonance modalities within the same regions and no such correlation survived corrections for multiple comparisons. Additionally, when participants with white matter lesions were excluded from the statistical analyses, the volume increase in frontal white matter correlated with Cho increase (r = 0.65, P = 0.044). Later onset of heavy drinking was associated with faster FA recovery in total white matter (r = 0.52, P = 0.008) and temporal white matter (r = 0.53, P = 0.024). Finally, none of the correlations was appreciably affected by exclusion of participants with depressive disorders, cardiovascular disease or history of drug abuse/dependence. The associations of volumetric and spectroscopic changes with cognitive measures and their changes with abstinence will be reported elsewhere in a larger cohort.