Fatigue in immune-mediated polyneuropathies. European Inflammatory Neuropathy Cause and Treatment (INCAT) Group.

To determine the prevalence and severity of ongoing fatigue and to investigate the internal consistency, reliability, and validity of the Fatigue Severity Scale (FSS) in patients with immune-mediated polyneuropathies. The FSS was assessed in 113 patients who either experienced Guillain-Barré syndrome in the past or currently have a stable, chronic, inflammatory demyelinating polyradiculoneuropathy or a polyneuropathy associated with a monoclonal gammopathy of undetermined significance, and in 113 age- and sex-matched healthy controls. Data on four additional scales (Medical Research Council sumscore, functional grading scale [f-score], INCAT sensory sumscore, medical outcome study 36-items health survey [SF-36]) were obtained in all patients. SF-36 also was assessed in 59 controls. "Severe" fatigue (FSS scores > or =95th percentile values in controls) was present in 80% of the patients. Fatigue was not significantly related to general strength, sensory deficits, f-score, and duration of symptoms. Severe fatigue was reported in 81% to 86% of patients with normal strength or sensation. Eighty percent of the patients (controls, 12%) reported their fatigue being among the three most disabling symptoms. SF-36 health status scores in the patient group were significantly lower than the obtained values of the controls and partially related to the FSS scores. Good internal consistency, significant reliability, and validity were obtained for the FSS. Fatigue is a major symptom in patients with immune-mediated polyneuropathies and may persist for years after apparent recovery. The Fatigue Severity Scale seems appropriate for assessing fatigue in these patients because good internal consistency, reliability, and validity were demonstrated.