Impairments in cognitive performance in chronic fatigue syndrome are common, not related to co-morbid depression but do associate with autonomic dysfunction, by
Lucy J Robinson, Peter Gallagher, Stuart Watson, Ruth Pearce, Andreas Finkelmeyer, Laura Maclachlan, Julia L Newton in  PLoS ONE 14 (2) [Published: February 5, 2019]

Research abstract:

To explore cognitive performance in chronic fatigue syndrome (CFS) examining two cohorts. To establish findings associated with CFS and those related to co-morbid depression or autonomic dysfunction.

Identification and recruitment of participants was identical in both phases, all CFS patients fulfilled Fukuda criteria. In Phase 1 (n=48) we explored cognitive function in a heterogeneous cohort of CFS patients, investigating links with depressive symptoms (HADS). In phase 2 (n=51 CFS & n=20 controls) participants with co-morbid major depression were excluded (SCID). Furthermore, we investigated relationships between
cognitive performance and heart rate variability (HRV).

Cognitive performance in unselected CFS patients is in average range on most measures. However, 0-23% of the CFS sample fell below the 5thpercentile. Negative correlations occurred between depressive symptoms (HAD-S) with Digit-Symbol-Coding (r=-.507, p=.006) and TMT-A (r=-.382, p=.049). In CFS without depression, impairments of cognitive performance remained with significant differences in indices of psychomotor speed (TMT-A: p=0.027; digit-symbol substitution: p=0.004; digit-symbol copy: p=0.007; scanning: p=.034) Stroop test suggested differences due to processing speed rather than inhibition.

Both cohorts confirmed relationships between cognitive performance and HRV (digit-symbol copy (r=.330, p=.018), digit-symbol substitution (r=.313, p=.025), colour-naming trials Stroop task (r=.279, p=.050).

Cognitive difficulties in CFS may not be as broad as suggested and may be restricted to slowing in basic processing speed. While depressive symptoms can be associated with impairments, co-morbidity with major depression is not itself responsible for reductions in cognitive performance. Impaired autonomic control of heart-rate associates with
reductions in basic processing speed.

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