Hypoglycaemia: Severe hypoglycaemia may cause cumulative cognitive deficits

Clinical bottom line (level 4)

  1. In patients with IDDM for >5years, a history of severe hypoglycaemia was correlated with an estimated decrease in IQ
Langan and Deary: Diabetologia 1991; 34: 337-344
Expires May 2003

The study

Case-control study with objective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: outpatients with IDDM of >5yrs duration in UK

100 patients (aged 40, 57% male) IDDM with age of onset >19yrs old

Excluded if
  • cerebrovascular disease
  • previous head injury
  • major psychiatric illness
  • medications that might alter cognitive functions
  • epilepsy
  • chronic excessive drinking of alcohol


    • Cases: 24 patients (58% male, mean age 37.9): patients with history of >5 episodes of severe hypoglycaemia
    Controls: 23 patients (48% male, mean age 38.5): patients with no reported history of severe hypoglycaemia


    Outcomes studied:

    The evidence

    • Difference in premorbid IQ and current IQ scores (premorbid IQ estimated with the NART test, current IQ by WAIS)
      • no severe hypoglycaemia episodes : 2.1 point decrement
      • repeated severe hypoglycaemia : 7.9 point decrement
    • Relationship between decrement in IQ and number of episodes of severe hypoglycaemia (r = -0.24 ; p<0.02 )
    • Severe hypoglycaemia was defined as an episode which required external assistance for recovery

    Comments

    1. No attempt made to control for confounding factors; are people who get hypoglycaemic more likely to have other factors for cerebral damage?

    Citation

    1. Langan SJ, and Deary IJ: Cumulative cognitive impairment following recurrent severe hypoglycaemia in adult patients with insulin-treated diabetes mellitus.. Diabetologia 1991; 34: 337-344
    Contributor: Matthew Taylor and Bob Phillips, May 1998
    Reviewer:

    Clinical Question.
    Patient adults with IDDM
    Intervention or Exposure does recurrent severe hypoglycaemia
    Outcome cause cognitive impairment