The interuncal distance in Alzheimer disease and age-associated memory impairment

To examine the value of measurement of the interuncal distance in the diagnosis of mild to moderate Alzheimer disease.

We measured interuncal distance from coronal MR scans acquired on a 1.5-T imager. We estimated interuncal distance from a total of 141 subjects: 54 patients diagnosed according to the National Institute of Neurological and Communicative Disorders and the Alzheimer's Disease and Related Disorders Association criteria of probable Alzheimer disease, 40 subjects fulfilling the National Institute of Mental Health criteria of age-associated memory impairment, 27 healthy cognitively normal older control subjects, and 20 control subjects younger than 50 years of age. For comparison we normalized interuncal distance for a horizontal line drawn through the inner cranium at the level of the uncus (interuncal distance/intracranial width ratio), for the brain area (interuncal distance/brain area) and for the intracranial area (interuncal distance/intracranial area).

The standard interuncal distance and the interuncal distance/intracranial width differed between the young control subjects and the other groups, but did not differ among the control, age-associated memory impairment, and Alzheimer disease groups. The Alzheimer disease group had significantly greater interuncal distance/intracranial area and interuncal distance/brain area compared with age-matched controls. A considerable overlap was found, however, in the values of patients with Alzheimer disease and control subjects. The cutoff point of 30 mm for interuncal distance yielded 37% sensitivity and 72% specificity to distinguish patients with Alzheimer disease from nondemented elderly subjects. Interuncal distance was not significantly related to the clinical severity of Alzheimer disease as assessed by Clinical Dementia Rating Scale and Mini-Mental Status Examination. Instead, there was a strong correlation between standard and normalized interuncal distance and age in the whole study population and in nondemented subjects.

Our results showed that in a series of 54 patients with mild to moderate Alzheimer disease, interuncal distance was not a reliable diagnostic tool. The study also confirmed the strong age dependence for interuncal distance.