No change in total length of white matter fibers in Alzheimer's disease.

White matter changes have been reported as part of Alzheimer dementia. To investigate this, the total subcortical myelinated nerve fiber length was estimated in postmortem brains from eight females (age 79-88 years) with severe Alzheimer's disease (AD) and compared with brains from 10 female control subjects (age 74-92 years). A stereological method for estimating myelinated brain fibers includes sampling systematically, randomly from the white matter, and counting fibers in unbiased counting frames using light microscopy at approximately 6000x magnification. The diameter of each counted fiber was measured to obtain the diameter distribution of myelinated fibers in both groups. The mean total myelinated fiber length was 81,554 km in the AD group and 78,896 km in the control group (P=0.63). All other measured parameters were also unaffected in the AD brains: The mean fiber length density was 248 km/cm3 in the AD group and 247 km/cm3 in the control group; the volume of white matter was 329 cm3 (AD) and 321 cm3 (control) and the volume density of myelinated fibers to white matter tissue volume was 0.30 in AD group and 0.31 in the control group. This is the first study of subcortical brain white matter fiber length using a stereological method on postmortem brains from AD patients and control subjects.