Reversible intellectual impairment: an internist's perspective.

A review of the relevant literature was stimulated by recent publications urging extensive laboratory assessment of elderly patients presenting with intellectual impairment. Published data regarding reversible causes of impairment are limited and exist only for hospitalized patients, with rare exceptions. The frequencies of azotemia, hyponatremia, volume depletion, hypoglycemia, cardiac arrhythmia, cerebrovascular disease, sensory impairment, hypercarbia, congestive heart failure, infections, subdural hematoma, and chemical intoxications as causes of the intellectual impairment are entirely unknown. It is reported that 8 per cent of patients hospitalized for dementia are depressed; alcoholism is causative in 8 to 13 per cent of patients with mental impairment; normal pressure hydrocephalus is reported in 7 to 12 per cent. The frequency of the latter conditions in outpatients is not known. While estimates exist for the frequencies of hypothyroidism, hyperparathyroidism, neurosyphilis, and vitamin B12 and folate deficiencies among the elderly, no prevalence data exist for these disorders among the intellectually impaired.