Conversion disorder
Individuals diagnosed with CD presented with highly distressing neurological symptoms such as numbness, blindness, paralysis, or convulsions, none of which were consistent with a well-established organic cause and could be traced back to a psychological trigger.
[1] CD is no longer diagnosed and was superseded by functional neurologic disorder (FND), a similar diagnosis that notably removed the requirement for a psychological stressor to be present.
FNsD covers a similar range of symptoms found in conversion disorder, but does not include the requirements for a psychological stressor to be present.
There have been a number of theories about this, such as the relative involvement of cerebral hemispheres in emotional processing, or more simply, that it was "easier" to live with a functional deficit on the non-dominant side.
However, a literature review of 121 studies established that this was not true, with publication bias the most likely explanation for this commonly held view.
In a highly influential[18] study from the 1960s, Eliot Slater demonstrated that misdiagnoses had occurred in one third of his 112 patients with conversion disorder.
[22] Treatments for conversion disorder included hypnosis, psychotherapy, physical therapy, stress management, and transcranial magnetic stimulation (TMS).
[26] Other treatments such as cognitive behavioral therapy (CBT), hypnosis, EMDR, and psychodynamic psychotherapy, EEG brain biofeedback need further trials.
Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades.
In 1976, large scale psychiatric registers in the U.S. and Iceland found incidence rates of 22 and 11 newly diagnosed cases per 100,000 person-years, respectively.
[8] Although it is often thought that the frequency of conversion may be higher outside of the West, perhaps in relation to cultural and medical attitudes, evidence of this is limited.
[36] Many authors have found occurrence of conversion to be more frequent in rural, lower socio-economic groups, where technological investigation of patients is limited and people may know less about medical and psychological concepts.
[30][34][36] The first evidence of conversion disorder dates back to 1900 B.C., when the symptoms were blamed on the uterus moving within the female body.
"[41] In Greek mythology, hysteria, a similarly described condition, was thought to be caused by a lack of orgasms, uterine melancholy, and not procreating.
Hippocrates argued that a lack of regular sexual intercourse led to the uterus producing toxic fumes, causing it to move in the body.
[41] Donald Capps argues that the diseases Jesus allegedly healed, such as paralysis and blindness, were actually forms of conversion disorder.
Gerolamo Cardano and Giambattista della Porta believed polluted water and fumes caused the symptoms of hysteria.
Jean-Martin Charcot argued that hysteria was caused by "a hereditary degeneration of the nervous system, namely a neurological disorder".
[45] As Peter Halligan comments, conversion has "the doubtful distinction among psychiatric diagnoses of still invoking Freudian mechanisms".
[46] Pierre Janet, a highly noted psychologist during the early 20th century, argued that symptoms arose through the power of suggestion, acting on a personality vulnerable to dissociation.
Some support for the Freudian model comes from findings of high rates of childhood sexual abuse in conversion patients.
[48] Support for the dissociation model comes from studies showing heightened suggestibility in patients with conversion disorder.
It is evidence of non-communication, of a mutual misunderstanding ... We are, often, unwilling to tell the full truth or to admit to ignorance ... Evasions, even untruths, on the doctor's side are among the most powerful and frequently used methods he has for bringing about an efflorescence of 'hysteria'".
As researchers identify the mechanisms which underlie conversion symptoms, it is hoped they will enable the development of a neuropsychological model.
