Myalgic encephalomyelitis/chronic fatigue syndrome and overlapping post-acute infection syndromes: international expert consensus framework for diagnostic standardization

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) lacks validated objective diagnostic criteria, leading to delayed diagnosis and inconsistent management. We aimed to establish an international expert consensus framework integrating measurable, risk-stratified assessments across seven core symptom domains. Using a modified nominal group technique with 19 multidisciplinary experts, consensus was achieved for all domains (participation 89.5–100%; agreement 94.7–100%). The framework defines provisional parameters for post-exertional malaise (PEM), autonomic dysfunction, cognitive impairment, functional decline, sleep disturbances, pain, and hypersensitivities. A tiered, color-coded clinical pathway was developed that prioritizes patient safety by escalating testing only when clinically essential. The framework provides provisional cut-offs for subjective and objective tools, emphasizing that thresholds currently lack prospective validation against fatigued disease controls. Because thresholds are provisional, these measures should currently support research standardization and cautious clinical exploration rather than definitive diagnosis. The framework provides a pragmatic, safety-first approach for standardizing functional assessment in ME/CFS and overlapping post-infectious conditions. Not applicable.