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Assessment and Differential Diagnosis
To diagnose any of the cannabis-related disorders, it is impor-tant to obtain a detailed history of the individual’s pattern of substance abuse (including abuse not only of cannabis but of other substances) and to attempt to substantiate this report with toxicology screening for drugs of abuse. Individuals who smoke cannabis regularly can have substantial accumulations of THC in their fat stores. Thus, for weeks after cessation of smoking, de- tectable levels of cannabinoids may be found in urine (Johnson, 1990). However, a positive response on toxicology screening for cannabinoids cannot establish any of the cannabis-related diag-noses; it is useful only as an indicator that these diagnoses should be considered.
It is uncommon to see patients who exhibit cannabis depend-ence as their only diagnosis because such individuals rarely seek treatment as they generally do not acknowledge that they have a problem and are unaware that treatment is available. However, some patients with this disorder will respond to offers for treat-ment because they realize that they are unable to stop use on their own and because they notice the deleterious effect of compulsive use (Roffman and Barnhart, 1987). Therefore, the diagnosis of cannabis dependence will most often be made in patients who present with other psychiatric problems, such as mood and anxi-ety disorders, and other substance use disorders. Another manner in which individuals with cannabis dependence may come to the attention of psychiatrists is when they are arrested for possession of the substance or some crime related to cannabis abuse, such as driving under the influence of the drug. Nevertheless, cannabis dependence is probably underdiagnosed in both psychiatric and general medical populations because it is not considered.
The diagnosis of cannabis dependence cannot be made without obtaining a history indicating that the cannabis use is impairing the patient’s ability to function either physically or psychologically. Areas to inquire about include the patient’s per-formance at work, ability to carry out social and family obliga-tions, and physical health. It is also important to find out how much of the patient’s time is spent on cannabis-related activities and whether the patient has tried unsuccessfully to stop or cut down on use in the past. Although it has been our experience that people who have used cannabis daily over a period of years almost invariably report tolerance to many of the effects of can-nabis and to experience an unpleasant withdrawal state if use is discontinued, neither tolerance nor withdrawal is necessary for the diagnosis of cannabis dependence. When this diagnosis is made, it can be described further by the following specifiers: with or without physiological dependence, early full or partial remission, sustained full or partial remission, or in a controlled environment. These diagnostic distinctions must be based on the pattern of use reported by the patient.
Most individuals who are diagnosed with cannabis abuse have only recently started using cannabis. As with cannabis depend-ence, cannabis abuse is unlikely to be diagnosed unless some additional condition or circumstance brings the individual to medical attention. Teenagers often fall into this category because they spend time in supervised environments like school and home where responsible adults may intervene. Also, teenagers are more likely to have motor vehicle accidents while intoxicated because they are inexperienced drivers, and are more likely to be arrested for possession because they have a greater tendency to participate in risky behaviors of all types.
Although virtually all individuals with cannabis depend-ence meet the inclusion criteria for cannabis abuse, they cannot be given this diagnosis because the presence of cannabis depend-ence is an exclusion criterion. Undoubtedly, the vast majority of people with cannabis dependence would have been given the diagnosis of cannabis abuse until they developed dependence.
It is probable that individuals qualifying for a diagnosis of can-nabis abuse will either cease use or develop cannabis dependence. The criteria for cannabis abuse focus on adverse consequences of cannabis use that could potentially re-sult from just a single use such as failure to fulfill obligations at work, school, or home, participating in potentially dangerous activities like driving while intoxicated with cannabis, having cannabis-related legal problems, or social or interpersonal dif-ficulties. Even though these adverse consequences can occur following a single episode of cannabis use, the consequences must be recurrent, requiring multiple episodes of use. Since the number of episodes necessary for “recurrent” is not defined, and the pattern of use is often dependent on patient self-report, it is often difficult to distinguish between abuse and dependence. This difficulty is easier to recognize if one looks at the extremes. On one end of the continuum, a high school student who actually has only used cannabis twice, but who was unfortunate enough to be caught and suspended from school on both occasions, would appropriately be diagnosed with cannabis abuse. At the other end of the continuum, a high school student who had actually been using cannabis every day for three years and met the criteria for dependence, who was also caught and suspended from school twice but denied symptoms of dependence, would incorrectly be diagnosed with cannabis abuse.
The difference between people with cannabis abuse and those with cannabis dependence is that the people with depend-ence have been using more regularly (one or more times per day) and for a longer duration (one or more years), and the acute prob-lems associated with abuse have turned into the chronic problems associated with dependence. For example, what started as failure to fulfill obligations at work or school has resulted in dropping out of school or working at jobs with extremely low expectations. Multiple car accidents or arrests have led to chronic injuries (of-ten associated with obtaining SSDI), loss of licenses, probation and even periods of time in prison. Social or interpersonal prob-lems have resulted in isolation or at least separation from people who are not regular cannabis users. If there is a committed rela-tionship where the partner is typically cannabis dependent, and if children are involved, chronic neglect is present if caring for children while intoxicated with cannabis represents neglect.
There are four criteria necessary to make this diagnosis (see DSM-IV criteria for intoxication). The first is that recent use of cannabis must be established. This cannot be done with toxicol-ogy screening because the result may be negative after a single episode of smoking or, alternatively, may be positive even if the individual has not used the drug for a time much longer than the period of intoxication (see section on Cannabis botany and phar-macology). Thus, the recent use of cannabis must be reported by the patient or another person who witnessed the patient’s use. In addition, the symptoms resulting from cannabis use must pro-duce “clinically significant maladaptive behavioral or psycho-logical changes”. Thirdly, the patient must exhibit some physical signs of cannabis use. DSM-IV-TR requires the patient to have at least two of four signs – conjunctival injection, increased ap-petite, dry mouth and tachycardia – within 2 hours of cannabis use. Fourthly, symptoms cannot be accounted for by a general medical condition or another mental disorder. There is a specifier, “with perceptual disturbances”, that can be used if the patient is experiencing illusions or hallucinations while not delirious and while maintaining intact reality testing.
There has been extensive research on the effects of acute cannabis intoxication. In addition to the symptoms and signs required for a DSM-IV-TR diagnosis, many psychological and physiological effects have been reported. Awareness of these may enhance the psychiatrist’s ability to recognize cannabis intoxica-tion. Physiological effects are listed in Table 37.2, and are divided into commonly observed effects and rare effects that have been described only after the use of very high doses of cannabis (Hall and Solowij, 1998; Ameri, 1999; Perez-Reyes, 1999). Cannabis has low toxicity, and to our knowledge, no deaths from canna-bis overdose have been reported (Hall and Solowij, 1998). Simi-larly, psychological effects are listed in Table 37.3, divided into commonly observed effects and uncommon effects. Most people find the commonly experienced psychological effects enjoyable. However, some individuals, especially women (Thomas, 1996)
and inexperienced users in an unfamiliar environment, find them frightening and experience anxiety and even have panic reactions (Hall and Solowij, 1998; Johns, 2001; Thomas, 1996). Although all of these effects typically persist only for the period of acute intoxication, some reports have described individuals who report “flashbacks” of cannabis intoxication long after use, and deper-sonalization persisting long after acute intoxication (Keeler et al., 1968, 1971; Levi and Miller, 1990; Annis and Smart, 1973; Stanton and Bardoni, 1972). At this time there is insufficient evidence to ascertain whether these reports are attributable to cannabis itself, to confounding factors such as the concomitant use of other drugs, or the presence of other Axis I disorders (Johns, 2001).
In addition, cannabis use produces deficits in a number of neuropsychological functions, both during acute intoxication and after up to a week or more of abstinence in chronic, long-term users. These tasks include short-term memory, sustained or divided attention, and complex decision-making (Ehrenreich et al., 1999; Pope et al., 1995, 1997, 2001a; Pope and Yurgelun-Todd, 1996; Schwartz et al., 1989; Solowij et al., 1991, 1995; Solowij, 1995, 1998). A study of chronic, long-term users found that these deficits were reversible after 28 days of abstinence (Pope et al., 2001a). However, a few studies have found that sub-tle electrophysiologic changes, of uncertain clinical significance, may persist even after years of abstinence (Solowij, 1995, 1998; Struve et al., 1998).
We have not located any original reports of this entity, although it is mentioned in various reviews and is included in DSM-IV. Thus, if cannabis intoxication delirium does occur in neurologi-cally intact individuals, it is probably a rare complication. If the delirium does not resolve within 24 to 48 hours, it is almost cer-tainly a result of an underlying neurological or medical condi-tion. Therefore, in a patient with delirium, even if recent cannabis use has been reported, a full diagnostic work-up should be per-formed to rule out a concomitant, treatable neurological condi-tion (Halikas, 1974; Johns, 2001).
The following two substance-induced conditions are not generally diagnosed unless the symptoms are in excess of those usually associated with the intoxication or withdrawal state and are sufficiently severe to warrant independent clinical attention.
There are two subtypes of cannabis-induced psychotic disor-der: one featuring delusions, the other hallucinations. The di-agnosis of this disorder is readily made in individuals who have psychotic symptoms that appear immediately after ingestion of cannabis. However, a careful history is required to establish whether the individual has a preexisting psychotic disorder (as is often the case in such situations) or whether the symptoms arose de novo after cannabis consumption. There is little evi-dence that cannabis-induced psychotic disorders can arise in previously asymptomatic individuals (Gruber and Pope, 1994). Therefore, if psychotic symptoms persist for 24 to 48 hours af-ter the period of acute intoxication, they are likely due to an underlying psychiatric disorder which must be diagnosed and treated (Hall and Degenhardt, 2000; Johns, 2001, Gruber and Pope, 1994).
This disorder may be further described by the following specifiers: with generalized anxiety, with panic attacks, with
obsessive–compulsive symptoms and with phobic symptoms. The literature contains papers that report individuals who have anxiety, panic reactions and paranoid ideation during the period of acute intoxication, but we are unaware of any papers that re-port obsessive–compulsive or phobic symptoms. People who ex-perience anxiety after using cannabis are typically inexperienced users who react to the novel experiences of perceptual distortions and intensified sensations with anxiety and even panic reactions, rather than enjoyment (Thomas, 1996; Johns, 2001; Szuster et al., 1988). Women are more likely than men to experience canna-bis-induced anxiety (Thomas, 1996). As with cannabis-induced psychotic disorders, we have been unable to find clear cases of cannabis-induced anxiety disorders in individuals without a preexisting Axis I disorder. Again, if symptoms of severe anxiety or panic persist for 24 to 48 hours after the period of acute intoxi-cation, they are likely due to an underlying psychiatric disorder that must be diagnosed and treated (Johns, 2001).
A diagnostic decision tree for cannabis use disorders is presented in Figure 37.1.
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