320 Somatic Symptom and Related Disorders
vance of this stress or trauma may be sugges ted by a close temporal  relationship. However,
while assessment for stress and trauma is im portant, the diagnosis should not be withheld
if none is found.
Conversion disorder is often associated wi th dissociative symptoms, such as deperson-
alization, derealization, and dissociative amne sia, particularly at symptom onset or during
attacks.
The diagnosis of conversion disorder does not require the judgment that the symptoms
are not intentionally produced (i.e., not feigne d), as the definite ab sence of feigning may
not be reliably discerned. The phenomenon of la belle indifférence  (i.e., lack of concern about
the nature or implications of the symptom)  has been associated wi th conversion disorder
but it is not specific for conver sion disorder and should not be  used to make the diagnosis.
Similarly the concept of secondary gain  (i.e., when individuals derive external benefits such
as money or release from respon sibilities) is also not specific to conversion disorder and
particularly in the context of definite evid ence for feigning, the diagnoses that should be
considered instead would include factitious disorder or malingering (see the section “Dif-
ferential Diagnosis” for this disorder).
Prevalence
Transient conversion symptoms are common, but the precise prevalence of the disorder is
unknown. This is partly because the diagnosis usually requires assessment in secondary
care, where it is found in approximately 5% of referrals to neurology clinics. The incidence
of individual persistent conversion sympto ms is estimated to be 2–5/100,000 per year.
Development and Course
Onset has been reported throughout the life course. The on set of non-epileptic attacks