Medical Matters: No lazy assumptions about patients with intellectual disability
By 2020, the number of people with intellectual disability aged over 65 is projected to double from estimates made in the 1990s. Photograph: Thinkstock
We have come a long way in the past 50 years in our attitudes to people with intellectual disability. Thanks to organisations such as St Michael’s House, people formerly labelled as having mental handicap are no longer hidden from public view or, as was the case for some, locked away.
Our first formal lecture on mental disability in medical school was given by the late Dr Barbara Stokes, the director of St Michael’s House. A paediatrician, she explained the various categories of mental disability, which were then largely based on cognition in the form of the person’s IQ. In general, an IQ score of less than 70 was the cut-off point for a diagnosis of mental handicap.
This somewhat sterile definition seemed at odds with my personal experience of intellectual disability. I was told that a close relative, now in her 60s, was moderately mentally handicapped. Yet she has a sharp sense of humour and an excellent memory. It seemed the IQ classification system in use when she was growing up took no account of these attributes.
Now, of course, intellectual disability is measured not just by IQ but also by assessing the person’s functional skills in everyday living. An adaptive behaviour rating scale is used to assess their communication, self-help and interpersonal skills.
We were also taught as medical students that people with an intellectual disability did not usually live much beyond 50. Possibly due to a focus on those with a genetic cause for their disability, such as Down’s syndrome, this prognosis has happily proved untrue.
Life expectancyAccording to the Irish Longitudinal study on Ageing (Tilda), life expectancy for those with intellectual disability continues to improve. In 2014 there were 27,887 people with intellectual disability in Ireland, and, as in other developed countries, they are now living longer. By 2020, the number of people with intellectual disability aged over 65 is projected to double from estimates made in the 1990s.
The main causes of intellectual disability are: genetic syndromes; problems during pregnancy such as foetal alcohol spectrum disorder or infection in the womb caused by viruses like rubella or zika; problems at birth, for example, when the baby is starved of oxygen; and diseases early in childhood such as measles, whooping cough and meningitis.
Researchers from Trinity College Dublin (TCD) who are working on the intellectual disability arm of Tilda highlight the issue of polypharmacy among older adults with intellectual disabilities. Writing in the journal BMJ Open, they say people with intellectual disabilities are likely to be exposed to multiple medicines to treat multiple chronic conditions; some 20 per cent of participants used 10 or more medicines while more than 30 per cent used between five and nine.
PolypharmacyLed by Prof Mary McCarron, the principal investigator for IDS-Tilda and dean of the faculty of health sciences at TCD, the researchers acknowledge that polypharmacy, when used appropriately, plays a critical role in maintaining health, but note “there is clear evidence that it is also associated with increased prescribing errors, and a higher prevalence of drug-related adverse effects as more drugs are prescribed”. Antipsychotics were the most commonly reported medicines (43 per cent) used by participants in the study followed by drugs to treat epilepsy (39 per cent) and laxatives (38 per cent).
These findings tie in with a study published in the current issue of the British Journal of General Practice. Compared with the general population, it found that patients with intellectual disability had a markedly higher prevalence of epilepsy, severe mental illness and dementia as well as moderately increased rates of hypothyroidism and heart failure. The prevalence of coronary heart disease and cancer was about 30 per cent lower than the general population.
These research papers show the importance of looking at the particular needs of patients with intellectual disability. Otherwise we risk repeating the lazy assumptions of the “mental handicap” years.