Onset Patterns and Course of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Observed Findings

• Infection-related events preceded symptom onset in 64% of subjects; stressful incidents in 39%; environmental toxin exposure in 20%.
• For 38% of subjects, >6 months elapsed between first symptom and meeting full ME/CFS criteria.
• During worst illness periods, 48% of subjects reported complete inability to engage in any productive activity.
• At time of survey, 47% were unable to work; only 4% reported steady improvement with 59% describing fluctuating course.
• Cognitive symptoms showed greatest temporal stability compared to other symptoms, which declined in prevalence over time.

Inferred Conclusions

• ME/CFS frequently follows identifiable triggering events, most commonly infections, suggesting possible infectious etiologies warrant investigation.
• Symptom evolution is heterogeneous, with some symptoms remitting while others persist or emerge, indicating complex underlying pathophysiology rather than simple fatigue state.
• The predominantly fluctuating or worsening disease course in this cohort challenges models of passive symptom resolution and suggests active pathobiologic processes.
• High comorbidity rates (97% with ≥1 other diagnosed condition) and familial clustering (13-27%) suggest possible shared genetic or environmental predispositions.

Remaining Questions