306 Dissociative Disorders
about 15% of all cases of depersonalization/derealization disorder, the symptoms are pre-
cipitated by ingestion of such substances. If the symptoms persist for some time in the ab-
sence of any further substance or medication  use, the diagnosis of depersonalization/
derealization disorder applies. This diagnosis is usually easy to establish since the vast ma-
jority of individuals with this presentation become highly phobic and aversive to the trig-
gering substance and do not use it again.
Mental disorders due to another medical condition. Features such as onset after age
40 years or the presence of atypical symptoms  and course in any individual suggest the
possibility of an underlying medical condition. In such cases, it is essential to conduct a
thorough medical and neurological evaluation, which may include standard laboratory
studies, viral titers, an electroencephalogram, ve stibular testing, visual testing, sleep stud-
ies, and/or brain imaging. When the suspicion of an underlying seizure disorder proves
difficult to confirm, an ambulatory electr oencephalogram may be indicated; although
temporal lobe epilepsy is most commonly implicated, pariet al and frontal lobe epilepsy
may also be associated.
Comorbidity
In a convenience sample of adults recruite d for a number of depersonalization research
studies, lifetime comorbidities were high for unipolar depressive disorder and for any
anxiety disorder, with a signific ant proportion of the sample having both disorders. Comor-
bidity with posttraumatic stress disorder was low. The three most commonly co-occurring
personality disorders were avoidant, borderline, and ob sessive-compulsive.
Other Specified Dissociative Disorder
300.15 (F44.89)