Subtyping Patients with Myalgic Encephalomyelitis (ME) and Chronic Fatigue Syndrome (CFS) By Course of Illness

Past research has subtyped patients with Myalgic Encephalomyelitis (ME) and Chronic Fatigue Syndrome (CFS) according to factors related to illness onset, illness duration, and age. However, no classification system fully accounts for the wide range of symptom severity, functional disability, progression, and prognosis seen among patients. This study examined whether illness trajectories among individuals with CFS were predictive of different levels of symptomology, functional disability, and energy expenditure. Of the participants (N=541), the majority described their illness as Fluctuating (59.7%), with 15.9% Constantly Getting Worse, 14.1% Persisting, 8.5% Relapsing and Remitting, and 1.9% Constantly Getting Better. The illness courses were associated with significant differences in symptomology on select domains of the DSQ, functioning on select subscales of the SF-36, and on overall levels of energy expenditure. The significant symptomatic and functional differences between groups suggest that subtyping patients with CFS according to illness course is a promising method for creating more homogeneous groups of patients. Keywords: Myalgic Encephalomyelitis; Chronic Fatigue Syndrome; Subtypes; Illness Course