• Neuropsychiatry
• Hysteria
• Movement Disorders
• Tourette Syndrome
• Myoclonus

In 2012, the upstate New York town of LeRoy became something of a neuropsychiatric battleground when it witnessed an outbreak of cases of sudden-onset tic-like behaviour in high-school age girls, many from a single school.1 The ‘Tourette's epidemic’, as it was dubbed by a fascinated world media, attracted different explanations: for every claim that this was ‘mass hysteria’ (ie, conversion disorder), there was an outraged counter-claim to the effect that such a diagnosis was missing a real organic cause of these tics and jerks, variously thought to be PANDAS (a rare and still controversial apparent autoimmune response to streptococcal infection), a response to human papilloma virus (HPV) vaccination or even the result of an environmental toxin.

While the dust has yet to settle on the diagnostic facts of the matter, interviews with patients, their families and many experts made abundantly clear how unpalatable a diagnosis of conversion disorder can be. The implication seems to be that these symptoms are somehow ‘less real’, ‘exaggerated’ or, worse, the product of some kind of deception.

In their serendipitously timed study, Heintz et al2 report on the neuropsychological profile of a series of 26 patients with ‘psychogenic jerky movement disorders’ (PMD), comparing this relatively understudied patient group with a neurological control group with Tourette syndrome and healthy controls. Unexpectedly, no major cognitive impairments were found in the PMD group despite a higher reported level of cognitive complaints in daily life. Although the test battery was somewhat limited and so more subtle cognitive deficits cannot be definitively ruled out, this is consistent with an emerging view that a deficit in the perception of or attention to one's abilities or bodily states, rather than a primary dysfunction in, for example, movement or cognition, may drive the maintenance of functional neurological symptoms.3 ,4

Interestingly, the PMD group performed worst on a test of symptom validity. These tests, designed to detect underachievement, are widely used in the diagnosis of malingering and have a role in forensic settings. Do these results imply that the patients in the study of Heintz et al were deliberately faking their symptoms? By implication, are the fears of patients and families who recoil from the diagnosis of conversion disorder in fact justified? Almost certainly not. Rates of non-credible responding are elevated in multiple other conditions including mild traumatic brain injury, chronic pain, psychogenic non-epileptic seizures and even ‘pure’ epileptic seizures. The nature of this list suggests that a simple distinction between ‘feigning’ and ‘not feigning’ is insufficiently fine-grained, in medicine generally and in the area of functional neurological symptoms specifically.5

A recent review of the traumatic brain injury literature by Jonathan Silver in this journal outlines a number of subtle (and, crucially, often ignored) psychosocial processes that may underlie poorer-than-expected performance on cognitive tasks.6 Particularly salient is the possibility that expectation, leading to increased attention to task demands, results in paradoxically poorer performance, in a situation analogous to ‘choking’ in professional sports. Clinically, a similar ‘blocking’ phenomenon is frequently encountered in the examination room when patients with functional neurological symptoms are asked to perform relatively simple tasks; this has been interpreted as further evidence for the primacy of attentional processes in the maintenance of these symptoms.7 The authors of the current paper acknowledge that perhaps the most that can be said is that their patients have put less effort than required into the tasks; according to Silver's analysis at least, even this may be saying too much. It is complexity of this kind that has motivated the call for the removal from DSM-V of the criterion, currently in DSM-IV, which demands that feigning be excluded before a diagnosis of conversion disorder is made.8

Further work also needs to be done on whether symptom validity tests have any diagnostic utility when assessing patients with possible functional neurological symptoms. It is unlikely that, when the next LeRoy-style outbreak occurs, a diagnosis of conversion disorder will be any easier to explain to patients or their family. But with sufficient thought given to the possibility of non-credible responding, the diagnosis might be that bit easier to make.