Effect of Case Management Interventions for Patients with Substance Use Disorders: A Systematic Review

Background Substance use disorder (SUD) is an important health problem that requires a complex range of care because of the chronic nature of the disorder and the multiple psychosocial problems involved. Current outpatient programs often have difficulties in delivering and coordinating ongoing care and access to different health-care providers. Various case management (CM) models have been developed, first for patients in other psychiatric domains and then for patients with SUD, in order to improve treatment outcomes. Aim This paper aims to assess the effectiveness of CM for patients with SUD. Methods We performed a systematic review of CM interventions for patients with SUD by analyzing randomized controlled studies published on the subject between 1996 and 2016 found on the electronic database PubMed. Results and conclusion Fourteen studies were included in the analysis. Differences between studies in outcome measures, populations included, and intervention characteristics made it difficult to compare results. Most of these studies reported improvement in some of the chosen outcomes. Treatment adherence mostly improved, but substance use was reported to decrease in only a third of the studies. Overall functioning improved in about half of the studies. The heterogeneity of the results might be linked to these differences between studies. Further research is needed in the field.

entering alcohol and drug outpatient clinics than patients with only SUD (6). This group of patients seems to have less access to aftercare services (7) and higher use of acute services, such as emergency room treatment and hospital services (8).
The period after discharge is characterized by a high risk of relapse, with most cases occurring within the first week of inpatient treatment (9). There is also an important risk of drug-related death (either accidental or intended) following a longer period of abstinence because of lower drug tolerance (10,11). These patients have multiple psychosocial problems for which they need support. Patient needs often remain unmet in current outpatient treatment programs (2), although the provision of help with legal advice, basic needs, and family services may improve patients' psychosocial functioning. Treatment continuity has been related to higher overall abstinence rates (12,13) and less frequent readmissions to hospital units (14). Between hospital and community care, treatment continuity is supposed to improve comprehensive support for patients.
Different strategies have been developed to improve treatment adherence and drug-related outcomes (15); among them, case management (CM) has been identified as potentially beneficial as suggested in early clinical studies (16). The definition of CM and its practice varies from place to place. In general, CM can be defined as a "coordinated integrated approach to service delivery, ongoing supportive care and help to access resources for living and functioning in the community" (17). This approach has been widely implemented in many different areas, such as insurance programs, education, and health care.
Given the complex, chronic, and relapsing nature of mental health disorders and SUDs, they require a broad and continuous approach such as can be offered by CM (17). Since the 1980s, this practice has been adapted for persons with SUD (18), but to date, only a few studies have described CM models for persons with SUD in Europe.
The aim of this study was thus to assess the effectiveness of CM for patients with SUD. We searched for published articles in which clinical CM was described for patients with SUD to help maintain treatment continuity and coordinate care after a patient was discharged from hospital or prison (transitional CM) or when a patient entered a treatment program.

MeTHOD
The electronic database PubMed was searched for empirical studies published between January 1996 and May 2016. The following keywords were used: "case management" AND "addiction"; "case management" AND "substance use disorder"; "case management" AND "substance abuse. " The inclusion criteria were as follows: randomized controlled trial, adult participants over the age of 18 years with SUD, and a CM intervention compared to treatment as usual (TAU).

ReSULTS
After checking for the inclusion criteria and for duplicates, we analyzed 14 studies (Figure 1). Details about the included studies are described in Table 1. One paper (19) was reviewed but excluded. It compared assertive community treatment to another form of CM intervention. In absence of a TAU comparison group, the study was not included.
The names of CM interventions varied in different studies. They were labeled "intensive, " "community, " or "assertive CM" (20)(21)(22); "strengths-based" (23)(24)(25)(26), "clinical" (27), and "transitional CM" (28); or "coordinated care management" (29) and "probation CM" (30). Although the names and interventions varied, certain common characteristics could be found. CM services were conducted by case managers with a professional background in nursing, social work, or mental health care (22). CM services were delivered mainly in the patients' communities and not at the treatment center or hospital (20)(21)(22). The length of interventions varied from 1 month (25) to 3 years (20), although 6 months to 1 year was the most common. The intensity of the CM intervention was rarely noted.

Study Populations
In some studies, the population had SUD and no further differentiation was made, whereas other studies considered specific subgroups such as patients in methadone programs (27), women with SUD (22,31,32), and participants with court judgments who were either incarcerated or in court-ordered treatments (23,28,30). Most studies were done in the United States, except for the one by Prendergast et al. (28) in Canada and Lindhal et al. (23) in Sweden.

Outcome Measures
The most frequently used outcome measures were change in drug or alcohol use, as well as adherence to SUD treatment (frequently measured in attendance rates) and linkage to other health-care providers. The other important outcome measures were healthcare use in terms of days of hospitalization, emergency ward visits, or health costs. On a more general level, some studies measured global functioning; employment rates; reduction of social, legal, and family problems; and client satisfaction. Two studies concerning incarcerated or court-ordered individuals also used the number of post-enrollment arrests as an outcome measure (28,30).
Most studies considered only SUD as an inclusion criterion. Surprisingly, the importance of comorbid mental health disorders or high service use was not defined as an inclusion criterion in most studies. Slesnick and Erdam's study (32) included only homeless mothers, and Morgenstern et al. 's studies (22,29,31) analyzed patients receiving welfare [in one study (22), only women were included]. Only Essock et al. 's study (20) used high service use, severe comorbid mental health disorder, unstable housing, and poor living skills as inclusion criteria. Some studies even excluded psychotic disorders (22,24), and Morgenstern et al. 's study (29) excluded patients who had been hospitalized more than once for mental health reasons in the past year. Five studies showed that substance use decreased (20,22,23,27,32), two papers (22,26) showed that the likelihood of initiating SUD treatment increased, and four publications (22,23,27,33) showed greater treatment retention when a case manager was involved in treatment. Four studies (23,24,33,34) showed improved access to health care and/or linkage between health-care providers. One research showed fewer days spent in hospital (20) but others reported an increased number of days in hospital, which is explained by the higher treatment retention (34). Seven publications showed better global functioning, which was described as more employment days (25,31,35). This was further differentiated in Morgenstern et al. 's study of 2008 (29), which showed that women were more likely than men to find employment when assisted by CM, to have fewer legal (21,35) and family problems (21), and to have better housing stability (32). Lindahl et al. measured very high patient satisfaction with the treatment and 100% treatment retention compared to TAU (23).

DiSCUSSiOn
In most studies, significant improvements were reported in the outcome measures. Substance use decreased in only five papers (20,22,23,27,32), but treatment adherence and linkage between health-care providers seemed to improve in most surveys, which is an important issue for this population and one of the main aims of CM. Overall functioning improved in more than half of the studies, which is in general linked to higher life satisfaction.
The two publications (28, 30) that did not find significant improvements in one of the outcome measures were both performed with incarcerated or paroled patients. In Guydish et al. 's paper (30), the important factor was the limited face-to-face time. Only 53.6% of participants had seen their CM once or more during the first 6 months. For those participants who had seen their CM two or more times in the first 6 months, there was an improvement in substance use and social problems. This finding shows how important treatment intensity of CM is for the outcome. The Proportion of women enrolled in SUD treatment or incarcerated was not statistically different for both groups. All other measures were not statistically different between groups. At 6 months, 53.6% of PCM participants met face-to-face with case manager once or more and at 12 months 43.5% did. In CG, this was 11.6 and 8.5%, respectively. This shows that the dosage was often a lot less than twice a month, as described in the intervention. The participants who had two or more contacts with case manager were more likely to have lower ASI rates and lower social severity rates Participants in both treatment conditions improved over time in multiple outcome domains, and few differences were found between the two models. Decreases in substance use were greater than would be expected given time alone. At the site that had higher rates of institutionalization, clients who received standard CM were more likely to be institutionalized. However, in the site that had lower rates of institutionalization, no differences in the rate of institutionalization were found between the two treatment conditions. At one site, the IG received a significantly higher dose (time and activities) of services than did the CG.  There were no significant differences between parolees in the TCM group and the SR group on outcomes related to participation in drug abuse treatment, receipt of social services, or drug use, crime, and HIV risk behaviors. For specific services (e.g., residential treatment, mental health), although significant differences were found for length of participation or for number of visits, the number of participants in these services was small and the direction of effect was not consistent   other study with a negative outcome, by Prendergast et al. (28), showed no improvement in treatment participation for parolees with SUD who were receiving CM. However, this finding cannot be generalized, as the case manager's adherence to the protocol and the intervention was not standardized. Moreover, the case manager seemed to have limited contact with the parolee and the parolees did not enroll voluntarily in the project. The studies are heterogeneous in their clinical approach, which limits our ability to generalize specific implications for practice. Different types of populations with different risk levels seem to account for the variation in readmission rates (36). For example, the study populations varied in illness severity (comorbidities and service use), which would most likely have an effect on the study outcome. Some comorbid populations were also excluded from surveys. The CM model is a specific intervention that seems more useful to specific subgroups who are unable to use existing health-care services. A large number of patients find adequate health care in the usual care programs, as shown in research on CM interventions that involve psychiatric patients with psychosis. Patients who benefit from CM have been shown to be those with greater social and psychosocial needs, more psychiatric symptoms, and higher service use (37), with others not needing this specific intensive care (38). If CM is applied to a large group, the effect on a smaller subgroup would likely be diluted and not as visible in the outcome measures. It will be important to further specify these subgroups in future in order to refer patients to the appropriate programs.
The intensity of application of CM differs in these studies, which also limits our ability to generalize the effects (39). These examples show the importance of face-to-face time with patients, which can be managed only with small caseloads. This seems to have been a limiting factor in the two studies (28, 30) mentioned above. In addition, the adherence to the model by the case manager and the voluntary participation of the patients seem to affect the outcome.
The majority of the studies were performed in the United States, which is a limiting factor in generalizing these findings to other countries such as those in Europe, where health systems differ in organization and funding. A further limitation of this research was that the data search was performed only on the PubMed database and possibly that unpublished negative studies were not taken into account. Furthermore, we did not differentiate between alcohol use disorder and other SUDs.

COnCLUSiOn
Most of the analyzed studies showed improvement in the chosen outcome measures, although these varied in different studies. Treatment adherence mostly improved, but substance use decreased in only a third of the studies. Overall functioning improved in about half of the studies. The differences in chosen outcome measures make it difficult to compare the results. The type of intervention and intensity of treatment also varied.
The heterogeneity of these results might be linked to the different types of populations studied. The specific CM intervention seems to be helpful only for specific subpopulations with SUDs. Further studies are necessary to determine inclusion criteria for CM treatment for patients with SUD in order to orientate those most likely to benefit from this approach to the specific CM programs.
Only a few studies on this intervention and SUD have been published. Further research is needed to examine the effect of treatment intensity of the CM intervention. Longitudinal studies are also needed in Europe to ensure the effectiveness of these treatments.

AUTHOR COnTRiBUTiOnS
LP, AM, and YK designed the strategy for the present review and drafted the manuscript. AM and LP searched for the references and read the manuscripts. LP, AM, and YK discussed the results. All authors reviewed the manuscript and helped with the final writing.