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Introduction
Mood disorders in those with intellectual disabilities (ID) can be thought of as “under-recognized yet over-treated.” They are under-recognized in that clinicians and caregivers can fail to recognize signs of mood disorders in those with ID. Instead, their behaviors are attributed to their disability, and when they are treated, because of misdiagnosis and the late stage at which they are addressed, the main treatment is medication, with polypharmacy being a risk. This chapter describes the main clinical features of mood disorders in people with ID and the similarities and differences in clinical presentation that occur when compared to the general population. It also reviews what is known about etiology and treatment for mood disorders in the ID population.
Diagnostic features
The Diagnostic Manual – Intellectual Disability (DM-ID; Fletcher et al., 2007) makes very limited adaptations to the standard diagnostic criteria, but does provide useful behavioral descriptions of symptoms of each disorder. In contrast, the Diagnostic Criteria for Psychiatric Disorders for Use with Adults with Learning Disabilities/Mental Retardation (DC-LD; Royal College of Psychiatrists, 2001) makes significant modifications to include symptoms commonly reported in individuals with ID not featured in the standard diagnostic criteria, such as the onset of or increase in aggression or other problem behaviors.
Depression
Individuals with ID are a highly heterogeneous group in relation to cognitive, communication, and social skills, even when comparing individuals with the same level of ID (Harris, 1998). The existing body of literature suggests that individuals at higher levels of intellectual ability present with psychiatric symptoms typically seen in the general population. The diagnosis in those with more severe levels of disability, however, is more complicated and is also more reliant on caregiver report due to challenges in communication. Consequently, the observational skills of the caregiver greatly affect the accuracy of the diagnosis. For example, Hurley (2008) found that depressed mood was infrequent as the chief complaint for patients with ID who were diagnosed with depression. It was instead the behavioral disturbance that prompted referral for psychiatric assessment. This suggests that caregivers may fail to recognize symptoms of depression and not seek psychiatric consultation in the absence of disturbed behavior.
The DM-ID (Charlot et al., 2007a), thus, recommends using a developmental approach to support diagnosis of depression, as has been done for children without ID. Such an approach considers how one’s developmental level impacts how depression is manifested, and includes irritable mood, for example, as a diagnostic symptom.
Mild/moderate ID
There is a general consensus that people with mild ID show a full range of mood symptoms and can be assessed with minimal adjustment to diagnostic criteria, providing the clinician has an understanding of the developmental level and adaptive skills of the individual, as even within the mild ID population, individual differences exist in the ability to identify and report internal states and thoughts. Furthermore, although individuals with mild and moderate ID are often grouped together in research studies, individuals with moderate ID may have significantly more difficulty reporting cognitive symptoms such as diminished ability to concentrate or excessive guilt compared to individuals with mild ID.
Severe/profound ID
Identification of depressive symptoms in individuals with severe or profound disability can be very challenging due to the intrinsic cognitive and communication limitations and atypical presentation of this population. Cognitive symptoms such as feelings of guilt, hopelessness, or suicidal ideation are rarely described (Ross and Oliver, 2003), and consequently these individuals are less likely to meet the full diagnostic criteria (Cain et al., 2003; Charlot et al., 2007b). Behavioral (or depressive) equivalents have been proposed as atypical symptoms of depression in individuals with severe disabilities. Self-injury, screaming, and aggression were identified as distinct symptoms of depression in Marston et al. (1997), but this finding has not been replicated (Tsiouris et al., 2003; Sturmey et al., 2010a). Furthermore, externalizing behaviors do not appear to be specific to mood disorders and research in this area suggests caution in using symptoms substitution. Instead, improving the reliability at the assessment level is recommended (Charlot et al., 2007b), with focus on core diagnostic features that can be observed (all symptoms excluding cognitive ones). Alterations in mood can manifest as a person crying every day, a decrease in laughing/smiling, and/or vegetative symptoms such as changes in eating (weight), sleeping, and motor activity (Lowry, 1998). Tsiouris et al. (2003) identified eight most frequently reported depressive symptoms in a research study where nearly half the subjects had severe/profound ID. These symptoms included: anxiety, depressed affect, irritability, loss of interest, social isolation, lack of emotion, sleep disturbance, and lack of confidence.
Bipolar disorders
Individuals with ID are more frequently diagnosed with a rapid cycling form of bipolar disorder (four or more episodes per year) than the general population. Abnormal mood states in individuals with ID diagnosed with bipolar disorder appear to be correlated with aggression. Given the recent inclusion of a new disorder of disruptive mood dysregulation (DSM-5) to mitigate overdiagnosis of bipolar disorder in young children, and the importance of considering developmental effects on mood disorders, there is a clear need to further investigate the course and nature of bipolar symptomatology in individuals with ID.
Mild/moderate ID
Similar to the presentation of depressive disorders, it appears that individuals with mild ID and good expressive language skills will show a full range of symptoms, and minimal adjustments to the diagnostic criteria will be required. The content of cognitive symptoms of mania (inflated self-esteem or grandiosity) may be simplified reflecting the developmental stage of the individual, such as a belief that the person can drive or is getting married when they do not have a partner. The mood may also be more irritable than expansive.
Severe/profound ID
The diagnosis of bipolar disorder is more difficult in individuals with severe or profound ID and affective symptoms may be difficult to distinguish from those related to developmental disabilities (Evans et al., 1995). The challenge is to “detect syndrome-specific affective behavior against a background of nonspecific behavioral responses triggered by a multiplicity of physiological, psychological, and social stimuli” (Sovner and Pary, 1993). While further work on symptom identification in this population is needed, a picture of core clinical features is slowly emerging. For example, psychomotor agitation, disturbed sleep patterns, and changes in mood and aggression correlated with the diagnosis of mania in a group of 15 adults with ID diagnosed with a bipolar disorder (Matson et al., 2007). Similarly, Sturmey et al. (2010b) found that a decreased need for sleep, restlessness, agitation, and irritability were associated with mania in adults with ID.
In this group, full diagnostic criteria for bipolar disorder will likely not be met due to limitations in verbal and cognitive abilities. Diagnosis could be made, however, based on observable criteria/behavioral correlates (Lowry, 1998). For instance, pressured speech may appear as increased vocalization or gesturing, and distractibility as moving from one activity to another, or not being able to complete activities of daily living.
Epidemiology
Considerable heterogeneity exists in the reported prevalence estimates of mood disorders among individuals with ID. Studies have reported prevalence rates of mood disorder ranging from 1.7% to 6.6% (Corbett, 1979; Lund, 1985; Cooper and Bailey, 2001; Cooper et al., 2007). A recent large-scale population-based Australian study with improved design found the prevalence rate of unipolar depression to be lower (0.9%; Morgan et al., 2008) than previously reported rates (2.2% –Deb et al., 2001; 4.1% – Cooper et al., 2007). An accurate assessment of psychopathology in ID is challenging for various reasons, and existing epidemiological studies suffer from significant methodological limitations, which impair generalizability of findings. Examples of such limitations include: (i) failure to report differences in the rates among mood disorders and its subtypes; (ii) failure to report if the rates are point prevalence or lifetime prevalence; (iii) inadequate or unclear case ascertainment; (iv) application of inadequate or variable screening instruments; and (v) variable composition and size of the study population. In a Scottish epidemiological study (Cooper et al., 2007), the prevalence rate increased when an ID-specific diagnostic instrument, the DC-LD (Royal College of Psychiatrists, 2001), was used, rather than relying on clinical diagnosis.
Some studies have suggested that mood disorders are more common in those with ID than those without ID (Richards et al., 2001), and that prevalence increases with age (Lund, 1985). However, other studies have not supported these findings (Deb et al., 2001; Cooper et al., 2007; Morgan et al., 2008)). The prevalence of depression is higher in women than men (Cooper et al., 2007), as has been found for the general population. No association has been reported between level of ID and depression (Cooper et al., 2007).
The reported prevalence of bipolar disorder (1.3%) is within general population estimates (Morgan et al., 2008). The prevalence of cyclothymia is about 0.3% (Cooper et al., 2007). A recent study examining hospitalized bipolar patients reported that compared to bipolar patients without ID, patients with ID tend to be younger and have significantly longer length of stay (Wu et al., 2013).
There is a considerable dearth of studies examining prevalence rates of mood disorders in children. Existing studies report varying prevalence rates of depression ranging from 1.5% to 4.4% (Dekker and Koot, 2003; Emerson, 2003); thus, very similar to the adult prevalence rates. No parallel epidemiological research has been conducted with regard to bipolar disorder in children.
Suicide. Existing studies clearly support the existence of suicidal behavior and completed suicide among individuals with ID (Lunsky, 2004; Lunsky et al., 2012), albeit the rates tend to be lower than in the general population (see Merrick et al., 2006 for review). Common methods include poisoning or cutting/stabbing. Individuals with ID who attempt suicide tend to be younger and are more likely to visit emergency departments than those who only express suicidal thoughts (Lunsky et al., 2012). Risk factors for attempted/threatened suicide in this population include female gender, a higher level of functioning, previous history of self-harm behaviors (Lunsky et al., 2012), unemployment, perceived stress, loneliness, depression, and anxiety (Merrick et al., 2006).
Etiology
Biological
The etiopathogenesis of mood disorders in ID is yet to be understood. Unfortunately, this has been generally a largely neglected topic in the contemporary psychiatric neuroscience research. The previously hypothesized direct association (Hurley et al., 2003) between ID and depression is yet to be confirmed. Important leads have mainly come from genetic research, and a few genetic syndromes have so far been associated with mood disorder in ID such as Fragile X syndrome, 22q11 deletion syndrome, tuberous sclerosis, Rubinstein–Taybi syndrome, Down syndrome, neurofibromatosis, phenylketonuria (Hassiotis et al., 2014), Prader–Willi syndrome, and Smith–Magenis syndrome (Kerner, 2014). Both depression and bipolar disorder have been associated with these genetic syndromes and, at this point, it is unclear if any of these syndromes has a specific association with any mood disorder subtypes. A recent literature review conducted by Walker et al. (2011) questioned the previous suggestion that depression is more common in people with Down syndrome.
Psychosocial
Psychosocial variables play an important role in the onset of mood disorders. Symptoms of depression have been associated with negative life events, low social support and stressful interpersonal relationships, and poor self-esteem (Esbensen and Benson, 2006). Negative social experiences including stigmatization, peer rejection, infantilization, and restricted access to employment opportunities have also been identified as risk factors for depression in the ID population (Morin et al., 2010). Trauma, more prevalent in those with ID than in those without, may also be a precursor to mood disorders (Wigham et al., 2011)
Assessment
The diagnosis of mood disorder depends on accurate identification of aspects of feeling and thinking, and observable behavior. Establishing baseline functioning, gathering information from multiple sources about diagnostically relevant changes in the mental status or behavior, and allowing a longer period of time for assessment, especially for bipolar disorder, are essential for accurate diagnosis of mood disorders in individuals with ID, particularly in those who cannot self-report. Use of assessment tools validated in the ID population is recommended.
Instruments for assessment of symptoms of depression
Several assessment measures have been developed to assess depressive symptoms specifically in individuals with ID. Two recent exhaustive reviews (Perez-Achiaga et al., 2009; Hermans and Evenhuis, 2010) compared psychometric properties of existing measures, including self-reporting, informant-based, and observation schedules. They concluded that most instruments require further research, particularly regarding sensitivity and specificity in the ID population; however, several promising instruments were highlighted.
Self-reporting
The Glasgow Depression Scale for people with a Learning Disability (GDS; Cuthill et al., 2003)is a 20-item scale for adults with mild to moderate ID. It also has a 16-item Carer Supplement (GDS-CS) that provides additional clinical information.
The Self-Report Depression Questionnaire (SRDQ; Reynolds and Baker, 1988) is a 32-item self-report questionnaire developed for individuals with mild ID.
Informant-based
Informant-based depression scales tend to be encompassed in instruments assessing broader psychopathology:
The Reiss Screen for Maladaptive Behaviour (RSMB; Reiss, 1998) is a 38-item questionnaire of psychiatric symptoms in adolescents and adults with mild to severe ID with two 5-item depression subscales, behavioral signs, and physical signs.
The Assessment of Dual Diagnosis (ADD; Matson and Bamburg, 1998) is a 79-item screen for psychiatric disorders in individuals with mild to moderate ID with an 8-item depression scale.
The Psychiatric Assessment Schedule for Adults with Developmental Disabilities Checklist (PAS-ADD Checklist; Moss et al., 1998) is a broad screen for mental health problems in individuals with ID with a 25-item affective/neurotic subscale.
Note: Instruments designed for use with the general population have been used with and without modifications with individuals with ID; however, their validation in this population is limited (Hermans and Evenhuis, 2010).
Instruments for assessment of symptoms of mania/affective disorder
There are several informant-based measures including the six-item Mania subscale of the Assessment of Dual Diagnosis (ADD; Matson and Bamburg, 1998); the five-item Manic/Hyperactive Behaviour subscale of the Anxiety, Depression and Mood Scale (ADAMS; Esbensen et al., 2003), suitable for all levels of ability; and the seven-item Mania scale of the Diagnostic Assessment for the Severely Handicapped–Revised (DASH-II; Matson, 1995), for use with individuals with severe/profound ID. Tools such as the Monthly Sleep Chart (Carr et al., 1998) and the Bipolar Mood Chart (Sovner and Desnoyers-Hurley, 1990) can also aid in the diagnostic process by documenting fluctuations in sleep and mood.
In addition, structured or semi-structured interviews based on the ICD or DSM criteria such as the Psychiatric Assessment Schedule for Adults with Developmental Disabilities (PAS-ADD; Moss et al., 1997) and the Mood and Anxiety Semi-Structured interview (MASS; Charlot et al., 2007a) can assist clinicians in evaluating both depressive and bipolar disorders.
Intervention and treatment
Pharmacological
See also Chapter 14.
Robust evidence of efficacy or safety regarding use of individual agents is lacking, as individuals with ID are either under-represented or excluded from clinical trials. Furthermore, it has been suggested that idiosyncratic and paradoxical reactions tend to occur at a higher rate in people with ID (Antochi and Stavrakaki, 2004; Stavrakaki et al., 2004), and recognition of adverse effects can be difficult in those who have limited communication abilities. Due to these factors, pharmacotherapy should be used cautiously and referral to specialist services should be considered for all complex cases.
The UK’s National Institute for Health and Care Excellence (NICE) recommends that when treating individuals with mild ID for depression, where possible offer the same evidence-based interventions utilized in the general population. Due to the favorable risk–benefit ratio, selective serotonin reuptake inhibitors (SSRIs) should be used as the first line of treatment for unipolar depression. Among SSRIs, the efficacy and safety of citalopram and fluoxetine are supported by open-label clinical trials in adults with ID (Howland, 1992; Verhoeven et al., 2001). The efficacy of paroxetine in the treatment of depressed adolescents with ID was also supported in one open-label study (Masi et al., 1997). With regard to bipolar disorder, the main treatment options include mood stabilizers and atypical antipsychotics. There is some evidence through case series that clozapine might be well tolerated and efficacious. Among mood stabilizers, valproic acid/divalproex has the most anecdotal support through case series and chart reviews (Buzan et al., 1998; Ruedrich et al., 1999; see also Chapter 13).
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