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Background: Patients with chronic fatigue syndrome (CFS) and post-Lyme syndrome (PLS) share many features, including symptoms of severe fatigue and cognitive difficulty., Objective: To examine the neuropsychiatric differences in these disorders to enhance understanding of how mood, fatigue, and cognitive performance interrelate in chronic illness., Methods: Twenty-five patients with CFS, 38 patients with PLS, and 56 healthy controls participated in the study. Patients with CFS met 1994 criteria for CFS and lacked histories suggestive of Lyme disease. Patients with PLS were seropositive for Lyme disease, had met the Centers for Disease Control and Prevention criteria, or had histories strongly suggestive of Lyme disease and were experiencing severe fatigue that continued 6 months or more following completion of antibiotic treatment for Lyme disease. All subjects completed self-report measures of somatic symptoms and mood disturbance and underwent neuropsychological testing. All patients also underwent a structured psychiatric interview., Results: Patients with CFS and PLS were similar in several somatic symptoms and in psychiatric profile. Patients with CFS reported more flulike symptoms than patients with PLS. Patients with PLS but not patients with CFS performed significantly worse than controls on tests of attention, verbal memory, verbal fluency, and motor speed. Patients with PLS without a premorbid history of psychiatric illness did relatively worse on cognitive tests than patients with PLS with premorbid psychiatric illness compared with healthy controls., Conclusions: Despite symptom overlap, patients with PLS show greater cognitive deficits than patients with CFS compared with healthy controls. This is particularly apparent among patients with PLS who lack premorbid psychiatric illness.

Fatigue is a prominent disabling symptom in a variety of medical and neurologic disorders. To facilitate research in this area, we developed a fatigue severity scale, subjected it to tests of internal consistency and validity, and used it to compare fatigue in two chronic conditions: systemic lupus erythematosus and multiple sclerosis. Administration of the fatigue severity scale to 25 patients with multiple sclerosis, 29 patients with systemic lupus erythematosus, and 20 healthy adults revealed that the fatigue severity scale was internally consistent, correlated well with visual analogue measures, clearly differentiated controls from patients, and could detect clinically predicted changes in fatigue over time. Fatigue had a greater deleterious impact on daily living in patients with multiple sclerosis and systemic lupus erythematosus compared with controls. The results further showed that fatigue was largely independent of self-reported depressive symptoms and that several characteristics could differentiate fatigue that accompanies multiple sclerosis from fatigue that accompanies systemic lupus erythematosus. This study demonstrates (1) the clinical and research applications of a scale that measures fatigue severity and (2) helps to identify features that distinguish fatigue between two chronic medical disorders.