The task of determining whether a patient is suffering from a substance-induced disorder or an independent psychiatric disorder can be complicated. Substances of abuse can cause a wide range of psychiatric symptoms. Clinicians evaluating such patients need to determine whether the disturbance is independent of substance use or related to intoxication or withdrawal. For example, when examining a patient who has a long history of alcohol dependence and depressive symptoms, it can be difficult to determine whether the depressive symptoms result from the direct pharmacological effects of alcohol, the many losses experienced as a result of the alcohol use, feelings of discouragement about the inability to stop drinking, or an independent mood disorder. Other etiologies, such as metabolic disturbances, head trauma, and personality disorders, must also be considered in the differential diagnosis of depressive symptoms in alcohol-dependent patients (Jaffe & Ciraulo, 1986).
Given these considerations, one could ideally establish diagnostic rules to assist in determining whether a psychiatric syndrome is due to substance use or represents a separate and independent disorder. For example, some clinicians may establish a rule that a patient must be abstinent from alcohol and drugs for at least 4 weeks before they can make a diagnosis. Unfortunately, one does not always have the luxury of observing such lengthy abstinent periods (either by historical report or in the present) to assess this. In such circumstances, guidelines, as opposed to strict rules, can be helpful. For example, several studies have indicated that for alcoholics with major depression, treating the depression can have a positive impact on drinking (Cornelius et al., 1997; Greenfield et al., 1998). Thus, while DSM-IV-TR (American Psychiatric Association, 2000) criteria for substance-induced mood disorder suggest at least 4 weeks of observation during abstinence before a clinician can diagnose an independent psychiatric disorder, it also recommends that clinicians should diagnose an independent disorder if the symptoms are qualitatively or quantitatively not what one would expect, given the amount and duration of the substance use. Certain disorders, such as eating disorders and PTSD, can be diagnosed readily, even in the context of substance use or withdrawal, since their symptoms do not closely resemble substance-related syndromes. Indeed, for a diagnosis such as PTSD, which tends to be underdiagnosed in SUD patients, the greater danger is to delay diagnosis; waiting for a period of abstinence may prevent needed treatment for the co-occurring disorder (Najavits, 2004).
Finally, clinicians should consider whether the patient's symptoms are what would be expected upon discontinuation of the abused substance. If there is considerable overlap between the observed symptoms and what one would expect from the drug discontinuation syndrome, then the clinician should wait until either (1) the symptoms resolve, or (2) the symptoms no longer are consistent with what one would expect from drug cessation (i.e., the syndrome one would expect to see after 1 week vs. 1 month of alcohol abstinence). Alternatively, if there is little overlap between the symptoms observed and the expected abstinence syndrome (e.g., bulimia nervosa in an opioid-dependent patient), then the diagnosis can be made without waiting.
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