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6 Patients affected by functional motor symptoms are not liars: an experimental deception study with the guilty knowledge task
  1. Benedetta Demartini,
  2. Roberta Ferrucci,
  3. Diana Goeta,
  4. Fabiano Ruggiero,
  5. Alberto Priori,
  6. Orsola Gambini


Objective The relationship between functional neurological symptoms (FNS) and feigning is not an easy one for many clinicians. Most neurologists do not see the two as entirely distinct and would rather not get involved in the uncomfortable business of distinguishing them. Research conducted in the past decades has tried to challenge a common clinicians’ view according to which patients affected by FNS are liars. Nevertheless, no study has systematically investigated deception in these patients.

Method Thirteen patients affected by functional motor symptoms and 14 healthy controls, matched for age and gender, underwent a modified version of the Guilty Knowledge Task (GKT), a computer-controlled procedure used to detect truthful and deceptive responses. All participants were also screened for depression (HAM-D), anxiety (HAM-A) and alexithymia

Results No significant difference was found between the two groups either in terms of reaction time (for true responses p=0.865, for false responses p=0.765), or in terms of accuracy (for true responses p=0.654, for false responses p=0.643). No significant correlation was found between responses at the GKT and HAM-D, HAM-A and TAS-20 score. Our data showed that patients affected by functional motor symptoms have the same capacity to lie than healthy controls. These results are reinforced by the fact that depression, anxiety and alexithymia did not correlate with the GKT responses, excluding they might represent confounding factors.

Conclusion Patients affected by functional motor symptoms are not liars. Clinicians should start considering these patients as genuine as patients with multiple sclerosis or Parkinson’s disease.

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