Patients show a heightened responsiveness to verbal suggestion

Patients with functional neurological disorder (FND) — defined as neurological symptoms unexplained by and incompatible with other neurologic or medical conditions — were more suggestible than other people, a meta-analysis suggested.

The results “corroborate the hypothesis that FND is characterized by heightened responsiveness to verbal suggestion,” wrote Devin Terhune, PhD, of the Goldsmiths’ College in London and co-authors, in the Journal of Neurology, Neurosurgery and Psychiatry. “Atypical suggestibility may confer risk for FND and be a cognitive marker that can inform diagnosis and treatment of this condition.”

FND appears to be common in neurology outpatient practice; a 2010 study found 16% of new referrals were for functional and psychological symptoms, second only to headache (19%). Suggestibility may be general (assessed by standardized behavior scales rating responses to general verbal suggestions) or related to specific symptoms (assessed by noting responsiveness to attempts to elicit symptoms using varied methods).

The meta-analysis included 11 studies of patients with FND that measured general suggestibility using standardized behavioral evaluation methods (FND n=316; control n=360) and 11 studies that assessed symptom suggestibility (FND n=1,285; control n=1,409).

Standardized mean differences showed that persons with FND had greater suggestibility than controls on standardized behavioral scales (SMD 0.48, 95% CI 0.15-0.81) and more responsiveness to suggestive symptom induction (SMD 1.39, 95% CI 0.92-1.86).

Induced symptoms were more frequent with FND than controls (49% versus 6%, respectively). “Suggestive symptom induction displayed high specificity (94%) although sensitivity is poor (49%), indicating that this technique is insufficient as a standalone diagnostic procedure,” Terhune and co-authors noted.

In an accompanying editorial, Stoyan Popkirov, MD, of Ruhr University in Bochum, Germany, and Timothy Nicholson, PhD, of King’s College London in England, noted that the “propensity for an idea to ’take possession of the mind and lead to its own fulfillment’ was considered a central element in FND pathophysiology by 19th-century neurologists.”

“Contemporary neurocomputational accounts have reformulated and reframed this concept: symptoms result from ’overly precise priors’ that can override contradictory sensory inputs, and the maladaptive tendency to drift towards such priors is a cardinal feature of FND,” they added. “Considering how integral these ideas are to our understanding of embodied cognition in general, and FND in particular, it is surprising how rarely suggestibility has been explored experimentally in patients with FND,” they wrote.

“The authors have succeeded in aggregating enough studies from a period of four decades in order to allow for a statistically sound assessment of this issue,” Popkirov and Nicholson wrote. “The results of the meta-analyses confirm what clinical practice has long suggested: compared with clinical and non-clinical controls patients with FND are indeed, as a group, moderately more suggestible in general, and their symptoms are much more likely to be induced through specific suggestive techniques.”

Suggestion has been studied in multiple psychiatric disorders including dissociative, stress, and somatoform disorders. A 2002 study found a correlation between hypnotic susceptibility and number of conversion complaints. Heterogeneity has been described; one earlier study posited two highly suggestible subtypes: a dissociative subtype with a predisposition to psychopathology and a subtype without clear deficits in functioning.

“The overlapping symptom profiles of these conditions imply an association between suggestibility and dissociative psychopathology,” the researchers noted.

A recent shift in diagnostic criteria for FND emphasized positive symptoms and de-emphasized an identifiable stressor preceding onset of symptoms. With this change, emerging theoretical models have distinguished when correspondence between the experience of symptoms and objective physiology in an individual is likely and when it is not. A 2012 model accounted for functional motor and sensory symptoms as an imbalance between prior beliefs and immediate sensory evidence.

Terhune and colleagues conducted their literature search in November 2019. Studies for general suggestibility included in the analysis were published between 1984 and 2009. Mean percentage of women in these studies was 86% for FND and 46% for controls. Mean age for FND was 31 and for controls 37.

Induced symptom studies included in the analysis were published between 1994 and 2018. Mean percentage of women in these studies was 77% for FND and 61% for controls. Mean age for FND was 33 and 37 for controls.

Study quality evaluation revealed multiple criteria were not reliably met. Only 5 of 22 studies (23%) documented that the experimenter was blind to group, and 3 (14%) demonstrated demographic comparability for patients and controls. No evidence of publication bias was found.

The most common FND diagnosis was non-epileptic seizure, with smaller numbers for mixed conversion disorder, somatization disorder, and psychogenic tremor.

“Results underscore the importance of personal, medical and social narratives in the manifestation of FND,” the editorialists observed.

“Suggestions can be formulated explicitly by a hypnotist making your arm feel heavy, but they can also be conveyed implicitly by a physician ordering an emergency brain scan or overemphasizing incidental findings,” they pointed out. “Clinicians need to be aware of the dense feedback loops that make up medical interactions and shape acute physiology as well as overarching illness narratives.”

Limitations of the meta-analysis include significant methodological variability across studies.

  1. Patients with functional neurological disorder (FND) — defined as neurological symptoms unexplained by and incompatible with other neurologic or medical conditions — were more suggestible than other people, a meta-analysis suggested.

  2. FND appears to be common in neurology outpatient practice; a 2010 study found 16% of new referrals were for functional and psychological symptoms, second only to headache (19%).

Paul Smyth, MD, Contributing Writer, BreakingMED™

The researchers reported no disclosures.

The editorialists reported no dsclosures.

Cat ID: 130

Topic ID: 82,130,130,192,925