The prognosis of functional limb weakness: a 14-year case-control study

Reliable data on the prognosis of functional motor disorder are scarce, as existing studies of the prognosis of functional motor disorder are nearly all retrospective, small and uncontrolled. In this study we used a prospectively recruited, controlled cohort design to assess misdiagnosis, mortality and symptomatic and health outcome in patients with functional limb weakness compared to neurological disease and healthy control subjects. We also carried out an exploratory analysis for baseline factors predicting outcome. One hundred and seven patients with functional limb weakness, 46 neurological and 38 healthy control subjects from our previously studied prospective cohort were traced for follow-up after an average of 14 years. Misdiagnosis was determined in a consensus meeting using information from records, patients and their GPs. Numbers and causes of death were collected via death certificates. Outcome of limb weakness, physical and psychiatric symptoms, disability/quality of life and illness perception were recorded with self-rated questionnaires. Outcome measures were compared within and between groups. Seventy-six patients (71%) with functional limb weakness, 31 (67%) neurological and 23 (61%) healthy controls were included in follow-up. Misdiagnosis was found in one patient in the functional limb weakness group (1%) and in one neurological control (2%). Eleven patients with functional limb weakness, eight neurological control subjects and one healthy control subject had died. Weakness had completely remitted in 20% of patients in the functional limb weakness group and in 18% of the neurological controls (P = 0.785) and improved in a larger proportion of functional limb weakness patients (P = 0.011). Outcomes were comparable between patient groups, and worse than the healthy control group. No baseline factors were independent predictors of outcome, although somatization disorder, general health, pain and total symptoms at baseline were univariably correlated to outcome. This study is the largest and longest follow-up study of functional limb weakness. Misdiagnosis in functional limb weakness is rare after long-term follow-up. The disorder is associated with a higher mortality rate than expected, and symptoms are persistent and disabling. It appears difficult to predict outcome based on common baseline variables. These data should help inform clinicians to provide a more realistic outlook of the outcome and emphasize the importance of active and targeted therapy.