NADD Bulletin Volume V Number 2 Article 2

Complete listing

Neuropsychological Assessment of Individuals With Dual Diagnosis

Michael Harvey, Psy.D.


Neuropsychological assessment of individuals with dual diagnosis presents challenges due to limited normative data and cognitive limitations in this population. This paper will present information on various models of neuropsychological assessment and will offer specific strategies for resolving referral questions for individuals with dual diagnosis.


Research shows that a majority of consumers with developmental disabilities exhibit identifiable abnormalities in brain function and that the prevalence, extent and nature of these neuropsychological deficits increases with the degree of cognitive limitations (Spreen, Risser, & Edgell, 1995). Neurological studies have shown that only 2.5 percent of children with moderate and severe mental retardation are free of neurological findings, while in contrast children in the mild range of intellectual disability exhibit fewer signs of neuropathology (p. 453). The incidence of seizure disorder increases in individuals with developmental disabilities as their level of measured IQ decreases (Barnhill, 1999). It is important to note that some form of identifiable neuropathology is found in a high proportion of individuals in the mild range of mental retardation (Spreen et al., 1995) and that the prevalence of diagnosed neuropsychiatric disorders is higher in consumers with dual diagnosis (Margolis, McInnis, Rosenblatt, & Ross, 1999).

The Historical Perspective: The “Flat Profile” Bias

Historically, professionals involved in the assessment of cognitive and neuropsychological functioning have assumed that individuals with intellectual disabilities exhibit relatively global deficits or flat depressed profile scores across all areas of functioning (Spreen et al., 1995). The assumption of global cognitive deficits in consumers with mental retardation arose in the context of the search by neuropsychologists and neurologists for instruments that would distinguish those individuals with “organicity” from normal populations (Lezak, 1995; Luria, 1973). This notion of a homogeneous population of individuals with “organicity” has been discarded in neuropsychology as research consistently showed individuals with differing etiologies for and areas of damage to the brain exhibited discrete profiles of relative strengths and impairment on neuropsychological tasks, and advanced neuroimaging techniques indicated that many cognitive abilities to be disassociable and involved increased metabolic activity and coordination between specific areas of the brain (e.g., Gourovitch et al., 2000; Crosson et al., 1999).

Although data clearly indicate that intellectual disabilities result from a wide array of etiologies (e.g., genetic, perinatal, hormonal, nutritional, metabolic, environmental, CNS insult, etc.) with differing neuropsychological profiles (Das, Naglieri, & Kirby, 1994; Cornish, Munir, & Cross, 1998; Gabel, 1986; Hooper, Boyd, Hynd, & Rubin, 1993; Klein & Mervis, 1999; McCaffery & Isaac, 1985; Munir, Cornish, & Wilding, 2000; Pulsifer, 1996; Spreen et al., 1995; Uecker & Nadel, 1998; Wang, 1996; Wang & Bellugi, 1994), the assumption that consumers with intellectual disabilities represent a homogeneous group continues to be reflected in the field. For example, the most current technical manual for the adult Wechsler scales (WAIS -III - WMS - III Technical Manual, 1997) reports little variability and global deficits for their restandardization sample of individuals with mental retardation. There was no consideration in the manual that took into account the relative insensitivity of IQ scores to neuropsychological impairment, potential sampling bias in the way consumers with intellectual disabilities were chosen for participation, and a lack of inclusion of working memory index scores in the study when working memory has consistently been found to be impaired relative to other areas of cognitive ability in consumers with mental retardation (e.g., MacKenzie & Hulme, 1987). Most published neuropsychological studies specifically exclude individuals with IQ scores < 70. This bias in the field and the reluctance of neuropsychologists to include consumers with mental retardation in their studies has served to slow research and limited the normative information available for this population.

Current Status of Neuropsychological Assessment: Issues of Sensitivity and Specificity

When considering neuropsychological assessment, it is important for professionals and consumers to be aware of the degree to which it may be sensitive to detecting various forms of disorder, such as dementia, and the degree to which it is specific in aiding clinicians in establishing a particular diagnosis and excluding others. A recent review by the Psychological Assessment Working Group of the American Psychological Association (Meyer et al., 2001) sought to examine the validity of psychological assessment and to compare the power of various psychological tests with medical diagnostic testing procedures through meta analysis. Results indicated that evidence for psychological test validity is strong and compelling. Specifically, neuropsychological assessment falls in the upper range of procedures (r = .68) and is more powerful diagnostically than many medical tests including the use of MRI imaging procedures to detect dementia (r = .57), the ability of CT imaging to detect metastases from head and neck cancer (r = .64), ultrasound results and identification of deep venous thrombosis (r = .60), and exercise ECG results and identification of coronary artery disease (r = .58) (p. 142 - 143). It is also clear that neuropsychological assessment is able to provide evidence for functional impairment in brain areas that current neuroimaging does not have the resolution to detect such as diffuse axonal injury after a traumatic brain injury (Lucas, 1998).

Integrative neuropsychological assessment, in the hands of a skilled and well-trained clinician, can be a key component in clarifying and developing a comprehensive understanding of the relationship between the functional abilities/deficits, personality structure, and interaction with the environment for consumers with dual diagnosis. It can be an extremely useful tool in developing effective treatment plans and strategies for dealing with complex challenging behaviors. This approach towards an integrative assessment can aid in diminishing the degree to which consumers with dual diagnosis and their care givers are likely to experience frustration, pain, or suffering.

Models of Neuropsychological Assessment

There are several models of neuropsychological assessment that offer more or less utility for the determination of functional abilities in consumers with dual diagnosis with varying degrees of cognitive impairment. The Empirical Normative Approach, often associated with the use of the Halstead-Reitan test battery (e.g., Jarvis & Barth, 1994), compares the performance of individuals on various neuropsychological tests with normative data. Demographic variables, in particular age, gender and education, have been found to have a significant influence on performance on many neuropsychological tasks. Given the limited norms available for individuals with intellectual disability, this approach is perhaps most valid and best utilized for consumers in the mild range of mental retardation.

The Boston Process Approach is based on detailed observation of the steps an individual takes in dealing with the demands of a task and the characteristics of the types of errors they make during their performance (Kaplan, 1988). Often data gathered in this approach involve testing the limits after standardized administration to effectively determine and specify the type of impairment an individual is exhibiting. For example, providing a multiple-choice response format for items failed on the WAIS-III information subtest to assess for the possibility of retrieval deficits. This testing paradigm has the advantage of flexibility and is not limited to normally distributed variables of neuropsychological performance. For example, developmental data have been gathered on strategies individuals use in completing copy, and recall conditions for the Rey Complex Figure and clock drawing. One disadvantage is the high degree of training and skill required of the examiner administering testing tasks. This approach may be useful and valid for consumers at all levels of intellectual disability and is only limited by the skill and ingenuity of the examiner.

The Hypothesis Testing Approach, formulated by Lezak (1995), determines the strategies for neuropsychological assessment on the basis of the referral question. Assessment of neuropsychological functioning in the Hypothesis Testing Approach may involve either normative or process methods of evaluation. Often they are combined together. This method of neuropsychological testing is flexible; hypotheses are developed on the basis of patterns and pathognomic signs noted in test responses and specific assessment instruments or procedures are used to evaluate them. This approach combines the best of both the empirical and process methods and places the examiner in the role of being a “detective” in regard to investigating potential neuropsychological issues. As Lezak (1995) notes for individuals with severe to profound mental retardation, possible solutions are to administer tests designed for use with children, elderly adults suspected of having brain damage, and to utilize qualitative tasks, such as those developed by Christensen and Luria, “to discern and discriminate functions at low performance levels that cannot be reduced to numbers” (p. 135).

It is important for clinicians engaged in the neuropsychological assessment of consumers with dual diagnosis to be trained in the evaluation of personality structure and this is an area that does not receive enough emphasis. The understanding of the interaction between an early onset of developmental disability, specific areas of neuropsychological impairment and life events in determining subsequent personality structure is key in developing an integrative conceptualization that can effectively inform treatment planning for consumers with dual diagnosis (e.g., Lezak, 1995; Rothstein, Benjamin, Crosby, & Eisenstadt, 1988; Sohlberg & Mateer, 2001). Increasingly, training programs in neuropsychology are turning away from developing clinical skills in personality assessment or psychotherapy, moving towards a cognitive neuroscience model rather than an integrative one. If specific recommendations are to be effective, it is important for clinicians engaged in neuropsychological assessment with consumers with dual diagnosis to have a comprehensive understanding of development, neuropsychology, personality structure, psychiatric disorders, life event and environmental factors that can influence adaptive functioning and the course of psychotherapy.

A Clinical Perspective: Distinguishing Developmental From Neuropsychological Issues

It is vital for clinicians engaged in the neuropsychological assessment of individuals with intellectual disability to do their best to distinguish between functional deficits that are the result of a failure to develop and impairments that result from a loss of brain function. As Denis (1988) points out, developmental failures result in the lag, detour and/or shortfall of age appropriate skills whereas brain insult or pathology results in a loss, or more accurately the suppression (see Stein, 1988) of an already established level of functionality.

Often individuals with dual diagnosis exhibit both types of difficulties. On an emotional level this differentiation is manifest in the struggle of consumers to come to terms with what Lacan (1981) termed “lack” versus “loss”. Lack can be conceptualized psychologically around issues consumers with dual diagnosis have with being “retarded” or “damaged from birth”. This sense of “lack” cannot effectively be put into words and is “something on the order of the non-realized ... the unborn” (p. 22 - 23). Certainly developmental disability represents a narcissistic injury to the parents’ hopes, dreams and aspirations for their child that, unless mourned and worked-through, results in a parental struggle with guilt that will impact subsequent personality development. Frequently this material emerges in the course of psychotherapy around the extreme ambivalence individuals with dual diagnosis have in regard to fantasies around reproduction, pregnancy and parenting, for example the notion that: “I damaged my mother because I was born retarded and if I have a child I will be destructive in making them retarded and forcing them to suffer the way I have”.

There are likely to be core conflicts for individuals with dual diagnosis in having to depend on others for aspects of their ego functioning that result in a dynamic that Levitas (1998) termed “the mediated self”. Consumers with dual diagnosis struggling with issues of “lack”, especially in the absence of a favored care giver who acts as a surrogate ego, may manifest a sense of perplexity, confusion, and the kind of psychic deflation, narcissistic in nature, that can be differentiated from the morbidity and self-reproach involved in a depressive process.

Loss involves a trauma to the individual that necessarily involves grieving and a process of working-through via mourning and letting go. People who experience neuropsychological insult may initially have a limited awareness of their loss that can result from a mixture of psychological denial and damage to specific areas of the brain (Sohlberg & Mateer, 2001). Over time, most individuals with neuropsychological impairment come to recognize their deficits and issues of grieving become salient. Consumers with dual diagnosis struggling with sadness over their losses may exhibit depressive symptoms, including excessive irritability, aggressive outbursts, self-reproach, and morbid thinking.

In completing a comprehensive neuropsychological assessment, then, it is important for the clinician to delineate and to specify the impact of each developmental failure from subsequent issues of loss of neuropsychological functioning over an individual’s life history. A review of case records and interviews with caretakers is vital in establishing these kinds of links within a time line. In this way an integrative framework for understanding a consumer’s current level of adaptive functioning, cognitive abilities, and personality structure can be effectively developed and used to formulate specific recommendations for habilitative services and psychotherapy.

Guidelines for Consumers and Care Givers

Make copies of important records and keep a developmental history so that they can be shared with professionals involved in assessment and/or caring for the consumer in the future.

Advocate for a comprehensive assessment of cognitive abilities, adaptive and neuropsychological functioning and personality structure. Having baseline data available for comparison with testing results in the future can improve the ability of a clinician to detect genuine neuropsychological as opposed to developmental impairment.

Know the qualifications and experience of professionals who may undertake a neuropsychological evaluation. Feel free to ask questions and to express your concerns.

Make sure the results of a comprehensive neuropsychological evaluation are used to formulate specific recommendations for habilitative services and psychotherapy that can be easily understood by caregivers, staff, the consumer and clinicians.


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For further information:

Michael Harvey, Psy.D.
Mountain Regional Services
P.O. Box 6005
Evanston, WY 82931-6005
(307) 789-0715; fax (307) 789-4774