Last updated: Mon, Jul 3, 2017
Conversion disorder is an impairment in the use of voluntary muscles or an impairment of sensation that resembles a recognized neurological or medical condtion. It is thought of as a subconscious loss of use of the muscles or senses, and in the past was sometimes called "hysterical" paralysis, deafness, etc. The two criteria for the condition are 1) the presence of the symptoms and 2) the examiner's judgment that psychological factors are important in its cause or continuation.
Weakness and sensory abnormalities that don't follow the dermatomes (called non-dermatomal sensory abnormalities or NDSAs) are very common among chronic pain patients. One study found that almost 40% of a group of chronic pain patients had NDSAs.1 Substantial evidence now exists that NDSAs are a function of the central physiology of pain. Strong or persistent activation of spinal synapses can activate neurons originating far apart in the body, thus creating the NDSA phenomenon. This has been verified in laboratory animals. PET studies have shown that NDSAs are accompanied by abnormalities in brain activation that are corrected once the pain has been controlled. In addition, NDSAs have been shown to occur only on the painful site or limb.
Muscle weakness is also associated with pain. A 20-30% reduction in strength is typical in a painful limb. Pain reduces both the maximal voluntary contraction and the endurance time for sub-maximal contraction. Studies of muscle activity show that muscle units fire more slowly when in pain. (See Inadequate Perception of Bodily States.)
This evidence indicates that the physical symptoms of conversion disorder (muscle weakness and sensory abnormalities) are strongly influenced by the presence of pain. This means that the diagnosis of “conversion disorder” in a pain patient must rest principally on the analyst's judgment of the importance of psychological factors. Or, as David Fishbain and his co-authors have put it:
Consequently and because the second criterion [that it is caused by pschological factors] is essentially a value judgment, it may be inappropriate to apply this diagnosis to any C[hronic]P[ain]P[atient] with these conversion symptoms, especially since there are medicolegal consequences in wrongfully applying this diagnosis.2
Ouch.