NADD Bulletin Volume I Number 4 Article 2

Complete listing

Diagnostic Dilemmas: The Diagnosis of Mental Illness in People with Mental Retardation

Geraldine Holt, Bsc, FRCPsych


The diagnosis of mental illness is complex , and is made after the clinician has taken a full history (often from other people as well as the patient), performed a physical and mental state examination, and perhaps proceeded to various investigations ( such as blood tests and EEG) and a period of behavioral observation. This can be a time-consuming process. It is also a controversial one. Kendell (1975) showed that clinicians presented with the same clinical material were liable to make different diagnoses. Yet given the many strands of information that need to be gathered together it would be unusual for different clinicians using the procedure described above to get identical sets of data on which to make a diagnosis and plan an intervention.

For those with mental retardation the complexities of making a diagnosis of mental illness are increased. This is reflected by the finding that mental illness in this population may go undetected (Moss and Patel, 1993). In this article I shall consider the reasons for this and how detection might be improved.

Possible contributors to missed diagnoses

There are a number of possible reasons why someone’s behavior might change, for instance a client may start slapping the side of his face because he has a physical problem such as toothache which he cannot explain to those who support him, this behavior may have been learned having been reinforced in the past by, for instance, staff viewing it as a sign of distress and allowing the client to avoid activities he does not like or by staff giving him more attention and reducing his boredom, it may also be a sign of distress in the context of a mental illness. If the client is to be helped to stop hurting himself then those that support him must be able to critically look at the situation and consider the various possibilities. Yet often staff in this situation have little experience of, or training in, mental health issues (Holt, 1995). It is, therefore, difficult for them to recognize mental illness or to know what action to take if they do.

All behavior occurs in a context, and it may be that a change in behavior as described above occurs in some settings, but not in others. Additionally, the same behavior may be viewed as a problem by some people and not by others.

In the general population mental health problems are sometimes identified by a person being less able to fulfill certain roles, for instance, mother, father, wife. People with mental retardation often do not have such roles and are not expected to carry out complicated activities, so that a slight change in their abilities may go undetected.

Some behaviors cause more concern than others. It is easy to understand that a client who becomes quieter and more withdrawn may not be viewed as distressed while the client who becomes physically aggressive to others is quickly identified as having a problem. Significant depression or anxiety may have no dramatic clearly defined outward manifestations, although distress to the person may be considerable.

If the possibility of mental illness has been recognized and the client is taken for a specialist mental health assessment there remain significant diagnostic issues. The communication difficulties of some people with mental retardation make understanding their distress a challenge. Even in those who have adequate speech, if they fall within the autistic spectrum of disorders they may be unable to describe their emotions. In the case of schizophrenia, the complexity of mental phenomena makes it unlikely that any but the most able of the developmentally delayed population can give a sufficiently clear account of symptoms for a confident diagnosis to be made.

Interpreting the information from an interview with someone with mental retardation can be further confounded by an increased tendency to acquiescence, with the client saying what he thinks the clinician wants to hear; and also the reduced attention span of some clients.

Given the significant difficulties of communication that many people with mental retardation have clinicians are more reliant on third party reports and observations. However, despite these issues it has been shown that interviewing the client reveals important and different information to reports from those who support them (Patel et al, 1993; Moss and Patel, 1993). Not surprisingly, support staff are more likely to be aware of symptoms with clear behavioral manifestations, than of personally experienced phenomena such as thought disorder or autonomic symptoms of anxiety (palpitations, tightness in chest, etc.). Also, while they may be aware of a person hearing voices, they are less likely to know what the nature of these is (which can be diagnostically crucial). They are also much less likely than clients to give clear accounts of worry, loss of interest, social withdrawal and irritability. Depending on the exact constellation of symptoms these differences in perspective may have a crucial impact on the diagnostic conclusions.

Improving the situation

It is vital to increase the awareness of those who support people with mental retardation with mental health issues. This can be achieved through training. Such awareness would alert them to the increased vulnerability of people with mental retardation to mental health difficulties (Menolascino, 1990) and increase their skills at anticipating likely precipitants, such as, changes in routine, bereavements, some medications, etc. This would enable them to take preventative action and to be responsive to a client’s distress. A training package with these aims has been developed in the U.K. (Bouras and Holt, 1997). It includes the PAS-ADD Checklist which is an instrument which support staff can use to screen for the possible presence of mental illness, and is described more fully below. If a mental illness is suspected, their training should have informed them as to how to access specialist mental health services and facilitate joint working.

There is also a need to improve the reliability and validity of diagnostic methods. Recent years have seen the development of a number of instruments designed to improve detection and diagnosis of psychiatric disorders in people with mental retardation. These include materials such as the Psychopathology Instrument for Mentally Retarded Adults (Kazdin et al, 1983; Senatore et al, 1985) and the Reiss Screen (Reiss, 1987). Researchers at the Hester Adrian Research Center at Manchester University in the U.K. have developed a multi-level approach to the assessment of mental health needs in those with mental retardation. The first two levels of the assessment process- the PAS-ADD Checklist and the Mini PAS-ADD- can be regarded as “filters” through which to identify people in the community whose mental health problems may have been hitherto unrecognized. The full PAS-ADD forms the final stage and is an in-depth mental state interview, and like the Mini PAS-ADD is designed for use by people who have undergone the appropriate training.

I. The PAS-ADD Checklist

As discussed earlier this is the first level of the assessment process. It is an observational screen of behaviors and symptoms commonly associated with mental health problems. It can be used to: (a) identify those at risk of mental health problems, (b) enable support staff to monitor changes and patterns in client behavior by routinely keeping standardized records, and (c) provides background information for subsequent psychiatric assessment. The PAS-ADD Checklist is designed primarily for use by support staff and family caregivers. It is quick and easy to complete. It is written in non-technical language, and no specific knowledge of mental illness is required. The Checklist covers eight broad areas of psychiatric disorder: depression, phobic anxiety, other anxiety disorders, hypomania, obsessive-compulsive disorder, schizophrenia, dementia and pervasive developmental disorders. It consists of twenty nine items, each referring to an observable psychiatric symptom. Caregivers record the presence or absence of symptoms observed during the previous four weeks on a four point scale: “has not happened”, “has happened but has not been a problem”, “ has been a problem for the person in the last four weeks”, “has been a serious problem”.

This provides three scores relating to different types of mental health problems: affective or neurotic disorder, possible organic condition (including dementia), and psychotic disorder. Thresholds are provided for each score. People who score over the threshold for any of the three scores should have their potential problem assessed further. The Checklist is designed to be over-inclusive so that all potential cases are recognized.

II. The Mini PAS-ADD

This provides a more detailed assessment of the mental state than the Checklist. It is a schedule aimed primarily at professionals such as psychologists, community nurses and social workers. It is completed either when a person has fulfilled enough criteria on the Checklist to indicate that further assessment would be beneficial or when a more detailed mental health assessment is warranted by some other means of referral. The Mini PAS-ADD provides a systematic framework within which to collect detailed information. Like the Checklist, assessment of a person’s mental health is based on observation of behaviors over the past four weeks. The person completing the Mini PAS-ADD is required, firstly, to decide whether a particular symptom is present or not and, if present, to decide, according to specific criteria set out in the rating instructions, whether the symptom is mild, moderate or severe. The schedule has eleven sections, comprising 69 items relating to the same eight psychiatric disorders as the Checklist. However, the Mini PAS-ADD is not an interview. It is for the systematic collection of information which is already known to a professional, or collectively by a group of professionals. It is advisable to consult with people who know the client well, and to make more detailed observations of the person’s behavior if there is uncertainty about symptom ratings. Like the Checklist the Mini PAS-ADD is designed primarily to identify persons with symptoms that indicate a need for further specialist psychiatric assessment, rather than to give a diagnosis. Upon completion, the Mini PAS-ADD provides scores and suggested thresholds. If the score attained is above the threshold then further assessment is recommended.


The PAS-ADD is a clinical interview for use by psychiatrists, which combines information from clients and their caregivers to produce an ICD-10 diagnosis. It provides standardized criteria and solutions aimed at overcoming specific problems of interviewing people with mental retardation. The PAS-ADD involves interviewing the client, followed by a similar interview of a key informant. Either interview can detect symptoms and produce diagnoses, so it can be used for those persons whose communication abilities do not permit a clinical interview. Administration of the instrument is guided by the number of psychiatric symptoms present. It consists of a number of filter items followed by more detailed questions if the item scores positively. It is semi-structured in format. The interview with each participant takes at least half an hour.


It is often difficult to understand the significance of behavioral change in someone with mental retardation. Sometimes, but not always, they are the result of mental illness, and this may go unrecognized. Those who provide support: staff and family, need to be aware of the vulnerability of people with mental retardation to mental health problems and what to do if they suspect mental illness. Training programs have a key role to play here. The use of the PAS-ADD Checklist helps staff to be more confident in their assessment of the situation.

Clinicians, in order to make an accurate diagnosis and appropriate treatment plan , need access to good quality information from people who know the individual well. This can be a time consuming process and it is often difficult to decide how to combine information from a variety of sources, and which may sometimes conflict. The Mini PAS-ADD is a useful tool to cope with these issues.

It is clear that the validity and reliability of diagnostic methods for this population needs to be improved. The PAS-ADD is described as an instrument designed to provide an ICD-10 diagnosis based on a semi-structured interview with the client and a key informant.


Bouras, N. & Holt, G. (1997) (eds): Mental Health in Learning Disability Training Package, 2nd. Edition. Pavilion Publishing: Brighton.

Holt, G. (1995): Training staff working in the community about the needs of people with a dual diagnosis. NADD Newsletter.

Kazdin, A., Matson, J. & Senatore, V. (1983): Assessment of depression in mentally retarded adults. American Journal of Psychiatry. Vol. 140, 1040-3.

Kendell, R. (1975): The role of diagnosis in psychiatry. Blackwell: Oxford.

Menolascino, F. (1990): The nature and types of mental illness in the mentally retarded. In Handbook of Developmental Psychopathology. Ed. Lewis, M. & Mill, S. Plenum Publishing corporation.

Moss, S. & Patel, P. (1993): Prevalence of mental illness in people with learning disability over 50 years of age, and the diagnostic importance of information from carers. Irish Journal of Psychology. Vol. 14, 110-129.

Patel, P., Goldberg, D. & Moss, S. (1993): Psychiatric morbidity in older people with moderate and severe learning disability (mental retardation). Part II: The prevalence study. British Journal of Psychiatry. Vol. 163, 481-491.

Reiss, S. (1987): Reiss Screen for Maladaptive Behaviour. International Diagnostic Systems, Inc.: Chicago.

Senatore, V., Matson, J. & Kazdin, A. (1985): An inventory to assess psychopathology of mentally retarded adults. American Journal of Mental Deficiency. Vol. 89, 459-66.

For further information contact:

Geraldine Holt, Bsc, FRCPysch
Division of Psychiatry & Psychology
UMDS-Guy’s Hospital
London, UK SE1 9RT