Exclusion of neurological disease => Conversion disorder presents with symptoms that typically resemble a neurological disorder such as stroke, multiple sclerosis, epilepsy or hypokalemic periodic paralysis. The neurologist must carefully exclude neurological disease, through examination and appropriate investigations. However, it is not uncommon for patients with neurological disease to also have conversion disorder.
In excluding neurological disease, the neurologist has traditionally relied partly on the presence of positive signs of conversion disorder, i.e. Certain aspects of the presentation that were thought to be rare in neurological disease but common in conversion. The validity of many of these signs has been questioned, however, by a study showing that they also occur in neurological disease. One such symptom, for example, is la belle indifférence, described in DSM-IV as "a relative lack of concern about the nature or implications of the symptoms". In a later study, no evidence was found that patients with functional symptoms are any more likely to exhibit this than patients with a confirmed organic disease. In DSM-V, la belle indifférence was removed as a diagnostic criteria.
Another feature thought to be important was that symptoms tended to be more severe on the non-dominant (usually left) side of the body. 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. Although agitation is often assumed to be a positive sign of conversion disorder, release of epinephrine is a well-demonstrated cause of paralysis from hypokalemic periodic paralysis.
Misdiagnosis does sometimes occur. In a highly influential study from the 1960s, Eliot Slater demonstrated that misdiagnoses had occurred in one third of his 112 patients with conversion disorder. Later authors have argued that the paper was flawed, however, and a meta-analysis has shown that misdiagnosis rates since that paper was published are around 4%, the same as for other neurological diseases.
Exclusion of feigning => Conversion disorder is unique in ICD-10 in explicitly requiring the exclusion of deliberate feigning. Unfortunately, this is likely to be demonstrable only where the patient confesses, or is "caught out" in a broader deception, such as a false identity. One neuroimaging study suggested that feigning may be distinguished from conversion by the pattern of frontal lobe activation; however, this was a piece of research, rather than a clinical technique. True rates of feigning in medicine remain unknown. However, it is believed that feigning of conversion disorder is no more likely than of other medical conditions.
Psychological mechanism => The psychological mechanism of conversion can be the most difficult aspect of a conversion diagnosis. Even if there is a clear antecedent trauma or other possible psychological trigger, it is still not clear exactly how this gives rise to the symptoms observed. Patients with medically unexplained neurological symptoms may not have any psychological stressor, hence the use of the term "functional neurological symptom disorder" in DSM-V as opposed to "conversion disorder", and DSM-V's removal of the need for a psychological trigger.
Conversion disorder begins with some stressor, trauma, or psychological distress. Usually the physical symptoms of the syndrome affect the senses or movement. Common symptoms include blindness, partial or total paralysis, inability to speak, deafness, numbness, difficulty swallowing, incontinence, balance problems, seizures, tremors, and difficulty walking. These symptoms are attributed to conversion disorder when a medical explanation for the afflictions cannot be found. Symptoms of conversion disorder usually occur suddenly. Conversion disorder is typically seen in individuals aged 10 to 35, and affects between 0.011% and 0.5% of the general population.
Conversion disorder can present with motor or sensory symptoms including any of the following:
Motor symptoms or deficits:
- Impaired coordination or balance
- Weakness/paralysis of a limb or the entire body (hysterical paralysis or motor conversion disorders)
- Impairment or loss of speech (hysterical aphonia)
- Difficulty swallowing (dysphagia) or a sensation of a lump in the throat
- Urinary retention
- Psychogenic non-epileptic seizures or convulsions
- Persistent dystonia
- Tremor, myoclonus or other movement disorders
- Gait problems (astasia-abasia)
- Loss of consciousness (fainting.
Sensory symptoms or deficits:
- Impaired vision (hysterical blindness), double vision
- Impaired hearing (deafness)
- Loss or disturbance of touch or pain sensatio.
Conversion symptoms typically do not conform to known anatomical pathways and physiological mechanisms. It has sometimes been stated that the presenting symptoms tend to reflect the patient's own understanding of anatomy and that the less medical knowledge a person has, the more implausible are the presenting symptoms. However, no systematic studies have yet been performed to substantiate this statement.