Methods: Some 960 adults with CFS were identified at four sites specializing in the diagnosis and treatment of CFS. Patients reported their demographics, CFS course, other medical diagnoses, and current functioning. We determined associations between: co-morbidities and a patient’s current health relative to their health when diagnosed with CFS; CFS symptom severity at onset and subsequent diagnosis with a co-morbid condition; and presence of a co-morbidity and functional ability. We also modeled the change in CFS symptom severity over time as it relates to the presence of a co-morbidity.
Results: Of the sample, 84% was diagnosed with one or more co-morbid conditions after CFS onset. Fibromyalgia, depression, anxiety, and hypothyroidism were the most common diagnoses. Nearly 60% of the sample reported a mental illness.
Conclusions: In general, co-morbid conditions reduced functional ability and were associated with the worsening of CFS symptoms over time. This study provides important new information on the prevalence of co-morbid conditions and their impact on the course of CFS.