The importance of classifying initial co-morbidity in evaluating the outcome of diabetes mellitus

Abstract

The associated co-morbid diseases present at the time of discovery of adult maturity-onset diabetes mellitus have not hitherto been quantitatively related to the subsequent course of the patients. From existing medical records and other solicited data, complete 5-yr follow-up was obtained for an ‘inception cohort’ of 188 patients who were treated during the years 1959–1962 at the West Haven VA Hospital and whose diabetes was first diagnosed within 6 months before ‘zero time’, which was the date of discharge for the ailment that had provoked hospitalization. A special classification was developed for categorizing the zero-time co-morbidity of the patients as prognostically cogent or non-cogent, and for dividing cogent co-morbidity into vascular and nonvascular types, with functional severity graded as none, moderate, and severe. The fatality rate at 5 yr after zero time was 40 per cent (76/188) for all patients, but distinctive gradients of fatality were noted for age, for type of co-morbidity, and particularly for severity of co-morbidity. The 5-yr fatality rate after zero time was 7 per cent in forty-one patients with no cogent co-morbidity, 33 per cent in seventynine patients with moderate co-morbidity and 69 per cent in sixty-eight patients with severe co-morbidity. Of the sixty-eight patients with severe initial co-morbidity, 53 per cent later died of the same or a related ailment; in the seventy-nine patients with moderate co-morbidity, the analogous death rate was 13 per cent. Death was due to ‘vascular causes’ in 52 per cent of seventy-seven patients who initially had vascular co-morbidity, in 7 per cent of seventy patients with nonvascular co-morbidity, and in 2 per cent of forty-one patients with no cogent co-morbidity. Among 5-yr survivors, the occurrence rate of new vascular events (or ‘diabetic complications’) was directly related to the same features of age and co-morbidity that seemed to affect fatality. These data indicate that the outcome of patients with maturity-onset diabetes mellitus depends on the type and functional severity of the co-morbid diseases present when the diabetes is detected. An appropriate analysis of co-morbidity, although omitted from existing statistical studies of diabetes, is pre-requisite to evaluating the results of different modes of therapy.