WHAT IS MENTAL RETARDATION INTELLECTUALLY DISABLED?
The DSM-1V2 defines mental retardation as follows:
- Significantly subaverage intellectual functioning-ie, an IQ of approximately 70 or below.
- Deficits or impairments in adaptive functioning.
- Onset before age 18 years.
Mental retardation is subdivided into levels of severity based on IQ and associated features (Table 1).
Individuals with mental retardation represent 1% to 3% of the general population. Mental retardation is approximately 1.5 times more common in boys than in girls.
Until recently, a significant proportion of individuals with mental retardation were cared for in residential facilities such as state-run training schools. Currently, however, the vast majority of the developmentally disabled live in the community and use community resources for treatment.
Mental retardation is highly heterogeneous as to cause. More than 250 biologic causes are known, most of which can be grouped under the general categories of chromosomal abnormalities, other genetic factors, prenatal and perinatal factors (eg, anoxia), acquired childhood disorders, environmental factors (eg, lead),3and sociocultural factors.
Knowing the cause in a particular case can sometimes provide important clues for understanding an individual's presentation; however, only approximately 25% of cases of mental retardation have a known biologic cause; in the remaining 75% of cases, the cause is unknown or is traceable to nonbiologic (eg, psychosocial) factors.
MENTAL RETARDATION AND PSYCHIATRIC DISORDERS
It has been estimated that 40% to 70% of individuals with mental retardation have diagnosable psychiatric disorders.4 This subgroup of individuals, however, are not the only ones who come in contact with psychiatrists. Like anyone else, a developmentally disabled person may present with emotional, behavioral, interpersonal, or adjustment problems that do not constitute major psychiatric disorders but that may benefit nonetheless from psychiatric input. Psychiatrists should remember that in clinical settings they do not have the opportunity to see people with mental retardation living and working in the community in a normal, non-problematic manner. As a result, they often do not have a baseline with which to compare current functioning.
Psychiatrists called on to evaluate and treat developmentally disabled individuals in either an emergency or inpatient setting need to be aware of special considerations that set this population apart. These considerations occur mainly in two areas: (1) working as part of a team with the patient's regular caregivers; and (2) characteristics of mental retardation that may confound the usual procedures for psychiatric diagnostic assessment and treatment planning.
Levels of Severity of Mental Retardation
Levels IQ Precentage of Mentally Retarded Population
50-55 to 70
35-40 to 50-55
20-25 to 35-40
Psychiatric care of individuals with mental retardation is most effectively rendered when the psychiatrist uses an interdisciplinary team model.5 The psychiatrist must take into account not only the acute problem but also the patient's relationship to long-term caregivers. These professionals tend to be deeply involved in the life of the patient, who they care a great deal about and see as their "client." They will likely contribute critically important diagnostic information and play a crucial role in implementing the treatment plan.
At the same time, referring caregivers sometimes distrust doctors and medications.4'6 This aversion may lead them to delay getting a consultation until they are "at the end of their rope" and feel as if they can no longer cope with the patient, whose condition may have worsened in the interim. They may simultaneously harbor unrealistic expectations, such as that the psychiatrist will be a magical rescuer. This ambivalence can have disruptive consequences. A successful treatment outcome may depend in part on how well the psychiatrist can bridge the gap between different conceptual models (medical versus habilitative), clinical languages, and organizational styles.
Special Diagnostic Issues
Mental retardation may obscure the standard diagnostic indicators of psychiatric disorders. For one thing, especially for the psychiatrist unaccustomed to the normal manifestations of mental retardation, those manifestations may overshadow symptoms attributable to psychiatric illness.7 Moreover, impairments in cognitive and verbal skills make it difficult for many developmentally disabled individuals to articulate abstract or global concepts such as a depressed mood. Most DSM-IV diagnoses require that the patient describe his or her internal state. Asking a person with an IQ below 40 about hallucinations, delusions, or guilt is seldom productive. On the other hand, the person's disorganized behavior may have diagnostic significance.8
These are the challenges that people with mental retardation often pose for psychiatric diagnosis. Sovner 9 identified four aspects of mental retardation that may influence diagnosis:
- Intellectual distortion - emotional symptoms are difficult to elicit because of deficits in abstract thinking and in receptive and expressive language skills.
- Psychosocial masking - limited social experiences can influence the content of psychiatric symptoms (eg, mania presenting as a belief that one can drive a car).
- Cognitive disintegration - decreased ability to tolerate stress, leading to anxiety-induced decompensation (sometimes misinterpreted as psychosis).
- Baseline exaggeration - increase in severity or frequency of chronic maladaptive behavior after onset of psychiatric illness.
To allow for these possible distortions, Sovner9 proposed that the standard diagnoses for mania and depression be modified, when applied to the developmentally disabled, to focus on biologic signs and symptoms and behavioral equivalents to subjective states.