LEARNING DISABILITIES

Health Evidence Bulletins - Wales

Literature searches completed on: 18th May 2000

 3:Epidemiology of Psychiatric Illness in Adults with Intellectual Disability

This bulletin is a supplement to, not a substitute for, professional skills and experience. Users are advised to consult the supporting evidence for a consideration of all the implications of a recommendation.

The Statements The Evidence
3.1 Psychiatric Illness
3.1a. Studies into the prevalence of psychiatric illness among adults with intellectual disability report a wide range, between 10% - 39%, depending on the sample selection; definition of psychiatric illness (some included and some excluded diagnoses such as behavioural disorders, pervasive developmental disorders, Rett syndrome and dementia); the diagnostic criteria used; and the diagnostic methods usedi. i. Borthwick-Duffy SA. Epidemiology and prevalence of psychopathology in people with mental retardation. Journal of Consulting & Clinical Psychology 1994; 62(1): 17-27
(Type V evidence – expert review of 8 observational studies between 1975 and 1985 involving adults with intellectual disability in both the hospital and community settings)
3.1b. It is not clear whether or not the rate of psychiatric illness increases with the severity of intellectual disabilityi,ii,iii.
It is difficult to decide with any degree of certainty whether mental illness in general but schizophrenia in particular is present in people with severe and profound intellectual disabilityiv.
i. Corbett J. Psychiatric morbidity and mental retardation. In Psychiatric Illness and Mental Handicap. (eds. FE James and RP Snaith). London: Royal College of Psychiatrists, Gaskell Press, 1979. pp.11-25
(Type IV evidence – cross-sectional study of psychiatric morbidity in a population-based sample of 140 children and 402 adults with intellectual disability in London)
ii. Göstason R. Psychiatric illness among the mentally retarded. A Swedish population study. Acta Psychiatrica Scandinavica, Supplementum 1985; 318:1-117
(Type IV evidence - cross sectional study of 51 severely and 64 mildly intellectually disabled adults and 64 control cases. Assessed using Comprehensive Psychopathological Rating Scale (CPRS) and DSM3 diagnostic criteria)
iii. Lund J. The prevalence of psychiatric morbidity in mentally retarded adults. Acta Psychiatrica Scandinavica 1985; 72(6): 563-70
(Type IV evidence – cross-sectional cohort study of 302 adults with intellectual disability, identified from the Danish National Register. It also draws comparisons with eight previous cross-sectional studies)
iv. Reid AH. Psychiatry and learning disability. British Journal of Psychiatry 1994; 164: 613-8
(Type V evidence - expert opinion)

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3.2 Psychiatric Illness in Elderly People
3.2a. Psychiatric morbidity is found in 61.9% of adults with intellectual disability aged over 65 years i. Among adults aged 50 years and over, the prevalence of psychiatric disorder excluding dementia is 11.4% and the prevalence of dementia is 11.4%ii. i. Cooper S-A. Psychiatry of elderly compared to younger adults with intellectual disabilities. Journal of Applied Research in Intellectual Disabilities 1997; 10(4): 303-311
(Type IV evidence - cross sectional study of 134 people over 65 years of age with intellectual disabilities)
ii. Patel P, Goldberg D, Moss S. Psychiatric morbidity in older people with moderate and severe learning disability. II. The prevalence study. British Journal of Psychiatry 1993; 163: 481-491
(Type IV evidence - cross sectional study of 105 people with intellectual disabilities aged 50 years and over, using PAS-ADD diagnostic interview)
3.3 Association of Psychiatric Illness with Other Disorders
3.3a. The rates of psychiatric illness as well as behavioural disorder in adults with intellectual disabilities and epilepsy are not significantly different from those in non-epileptic adults with intellectual disabilitiesi,ii. i. Deb S. Mental disorder in adults with mental retardation and epilepsy. Comprehensive Psychiatry 1997; 38(3): 179-84
(Type IV evidence – case-controlled study of 150 epileptic and an age-, sex- and IQ-matched control group of 150 non-epileptic adults with intellectual disabilities)
ii. Deb S, Joyce J. Psychiatric illness and behavioural problems in adults with learning disability and epilepsy. Behavioural Neurology 1998; 11(3): 125-9
(Type IV evidence - cross-sectional study of 143 adults with intellectual disabilities and epilepsy)
3.3b. The rate of functional psychiatric illness (excluding dementia and behavioural problems) in adults with severe intellectual disabilities but not Down syndrome is six times higher than adults with intellectual disabilities and Down syndromei.

Controversial evidence exists as to the higher rate of depressive illness reported among people with Down syndrome compared with non Down syndrome adults with an intellectual disabilityi,ii.

i. Haveman MJ, Maaskant MA, van Schrojenstein HM, Urlings HFJ, Kessels AGH. Mental health problems in elderly people with and without Down’s syndrome. Journal of Intellectual Disability Research 1994; 38(3): 341-55
(Type IV evidence - cross sectional study comparing 209 severely and 59 mildly intellectually disabled adults with Down syndrome with 477 severely and 1255 mildly intellectually disabled adults without Down syndrome)
ii. Collacott RA. Cooper SA. McGrother C. Differential rates of psychiatric disorders in adults with Down's syndrome compared with other mentally handicapped adults. British Journal of Psychiatry 1992; 161:671-4
(Type IV evidence – case-controlled study of 371 adults with Down syndrome compared with 371 matched adults with intellectual disabilities of causes other than Down syndrome)

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3.4 Prevalence of Specific Psychiatric Illnesses in Adults with Intellectual Disability
3.4a. Studies into the prevalence of specific psychiatric illnesses amongst adults with intellectual disability indicate that some conditions are more prevalent than others in people with intellectual disabilityi,ii,iii,iv.
The point prevalence of schizophrenia is reported as between 1.3% and 3.7%.
The point prevalence of affective disorders including depressive illness and mania are reported as between 1.2% and 6%.
The point prevalence of anxiety related neurotic disorders is found in around 16.4% adults (20-64 years).
i. Turner TH. Schizophrenia and mental handicap: an historical review, with implications for further research. Psychological Medicine 1989; 19(2): 301-14
(Type V evidence – expert review of 9 English language studies published between 1968 and 1985)
ii. Lund J. The prevalence of psychiatric morbidity in mentally retarded adults. Acta Psychiatrica Scandinavica 1985; 72(6): 563-70
(Type IV evidence – cross-sectional cohort study of 302 adults with intellectual disability, identified from the Danish National Register. It also draws comparisons with eight previous cross-sectional studies)
iii. Hagnell O, Öjesjö L, Otterbeck L, Rorsman B. Prevalence of mental disorders, personality traits and mental complaints in the Lundby study. Scandinavian Journal of Social Medicine. Supplementum. 1993; 21(Suppl.50): 1-76
(Type IV evidence – cross-sectional study of a geographically defined total population of 2612 over a 25 year period)
iv. Cooper SA. Psychiatry of elderly compared to younger adults with intellectual disability. Journal of Applied Research in Intellectual Disability 1997; 10(4): 303-11
(Type IV evidence - cross sectional study of 134 people over 65 years of age with intellectual disability, and 73 people aged 20-64 years with intellectual disability)
3.4b. The prevalence of attention deficit hyperactivity disorder (ADHD) amongst adults with severe and profound intellectual disability (15%) is similar to children with severe intellectual disability (18%), but higher than in children with average intelligence (3%-5%)i. i. Fox RA, Wade EJ. Attention deficit hyperactivity disorder among adults with severe and profound mental retardation. Research in Developmental Disabilities 1998; 19(3): 275-80
(Type IV evidence - cross sectional study of 86 adults with severe to profound intellectual disability from a community setting, using the Conner’s (1990) Hyperactivity Index)

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3.4c. There is an association between depression and aggression with 40% of adults, adolescents and children with both intellectual disability and depression exhibiting aggressioni. i. Reiss S, Rojahn J. Joint occurrence of depression and aggression in children and adults with mental retardation. Journal of Intellectual Disability Research 1993; 37(3): 287-94
(Type IV evidence - cross sectional study of 528 adults, adolescents and children using Reiss scale)
3.5 Services for people with Psychiatric Illness and Intellectual Disability
3.5a. Up to 5 years after community resettlement, people with intellectual disability show little change in the prevalence of psychiatric diagnoses or behavioural disturbancei.
(Health gain notation – 4 "unknown")
i. Kon Y, Bouras N. Psychiatric follow-up and health services utilisation for people with learning disabilities. British Journal of Developmental Disabilities 1997; 43(1): 20-26
(Type IV evidence - cross sectional study with 1 and 5 year follow ups of 74 adults with intellectual disability following resettlement in the community)
3.5b. Outreach treatment represents an effective and efficient alternative to hospital treatment for people with intellectual disability and psychiatric disordersi,ii.
(Health gain notation – 2 "likely to be beneficial")
Assertive community outreach treatment or intensive care (caseload, 10-15) significantly decreased the bed use and hospital admission in people with borderline intelligence and psychiatric illness when compared with those who receive standard community care (caseload 25-35)iii.
i. van Minnen A, Hoogduin CAL, Broekman TG. Hospital vs. outreach treatment of patients with mental retardation and psychiatric disorders: a controlled study. Acta Psychiatrica Scandinavica 1997; 95: 515-22
(Type II evidence - 28 week follow-up of 50 patients with intellectual disability referred for psychiatric admission: patients randomly allocated to outreach or hospital inpatient treatment)
ii. Holden P, Neff JA. Intensive outpatient treatment of persons with mental retardation and psychiatric disorder: a preliminary study. Mental Retardation 2000; 38(1): 27-32
(Type III evidence – non-randomised controlled study of 28 adults with intellectual disability and severe psychiatric disorder)
iii. Tyrer P, Hassiotis A, Ukoumunne O, Piachaud J, Harvey K. UK 700 Group. Intensive case management for patients with borderline intelligence. Lancet 1999; 354: 999-1000
(Type II evidence – randomised controlled trial of 708 patients, followed up for two years)
3.5c. 17% of all referrals to psychiatrists of people with intellectual disability were considered emergenciesi.
The majority of emergency referrals present as behavioural problems such as severe physical aggression and self-injurious behaviour.
i. Kohen D. Psychiatric emergencies in people with a mental handicap. Psychiatric Bulletin 1993; 17: 587-9
(Type IV evidence - 12 month prospective study of referral patterns in a London borough)

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