What is the clinical evidence from this study?

Study design: Observational. Population: Chronic fatigue syndrome (n=119). Intervention: Chronic fatigue syndrome vs. Community controls. Primary outcome: Digit-Symbol Substitution (symbols per minute) (MD 7.52, 95% CI 2.78-13.25, p=0.004).

February 5, 2019Open Access

Impairments in cognitive performance in chronic fatigue syndrome are common, not related to co-morbid depression but do associate with autonomic dysfunction

Key Result

Chronic fatigue syndrome without co-morbid depression was associated with significant impairments in psychomotor speed, including fewer digit-symbol substitutions per minute compared to controls (MD 7.52, p=0.004).

Study Design

Type

Observational (n=119)

Multicenter

Structured PICO

Population

119 participants across two cohorts, including 99 patients with chronic fatigue syndrome and 20 community controls, assessed for cognitive performance and autonomic dysfunction.

Comparator

Community controls (for Cohort 2)

Outcome

Cognitive performance across multiple domains (psychomotor speed, memory, executive function) and its relationship with depressive symptoms and heart rate variability (HRV)surrogate

Cognitive difficulties in chronic fatigue syndrome are primarily related to slowed basic processing speed, which persists independent of major depression and correlates with reduced autonomic function.

Main Result

Mean Difference: 7.52 (95% CI 2.78–13.25)

Absolute Event Rate: 35.2% vs 42.7%

p-value: p=0.004

Limitations

Sub-threshold depressive symptoms were not recorded in cohort 2
Cohort 1 and 2 described depressive symptomatology using different tools
CFS remains a poorly defined heterogenous condition with subjective diagnostic criteria
Correlative nature of the heart rate variability findings without error correction applied to the analyses

Abstract

OBJECTIVES: 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. METHODS: 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 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). CONCLUSION: 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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