Phencyclidine (PCP)-Related Psychiatric Disorders Workup
- Author: Alan D Schmetzer, MD; Chief Editor: Iqbal Ahmed, MBBS, FRCPsych(UK) more...
Always obtain a urine drug screen for a person with agitation or psychosis, unless the patient is so well known to the treating physician and staff that there is no question at all regarding the cause of the abnormalities observed. Even then, if the clinical picture seems at all different from the usual presentation, a drug screen may be useful. Serum levels of specific drugs also may be available in some emergency departments. However, be aware that specific urine or serum levels may have little correlation with clinical manifestations, especially in the case of PCP intoxication.
Phencyclidine is excreted in the urine, both in unchanged form and as conjugated metabolites. The usual laboratory test for PCP is an enzyme immunoassay technique that detects both PCP and its metabolic analog, 1-[1-(2-thienyl)-cyclohexyl]-piperidine (TCP). This is a qualitative screening test; that is, it tells whether the drug is present or absent. Gas chromatography coupled with mass spectrometry (GC/MS), as with other drugs, is the confirmatory test providing the highest confidence level for PCP.
Because rhabdomyolysis is a potential complication of PCP intoxication, serum enzyme levels may be useful, particularly skeletal muscle creatine phosphokinase (CPK).
Imaging studies have not proved clinically useful as yet in delineating PCP-induced psychosis from other causes of such disorders. Brain imaging studies in small numbers of adult chronic PCP users suggest that they may have decreased right cerebral cortical blood flow and frontal glucose metabolism. Such abnormalities are similar to those found in patients diagnosed with schizophrenia. Eventually it is hoped that diagnostic clues to PCP psychosis may be found from more complex imaging techniques than those currently available.
PCP use may begin as recreational and intermittent, but some evidence suggests that people can progress to abuse and finally, possibly, to dependence.
In addition, assess for stage of change. This includes whether the patient is in the "precontemplation," "contemplation," "planning," "action," or "maintenance/relapse" phase of decision making (as described by Prochaska and DiClemente) regarding his or her use of PCP.
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