Bicaudate diameter--the most specific and simple CT parameter in the diagnosis of Huntington's disease.

In addition to the neurological findings, the functional capacity of 12 patients with Huntington's disease was evaluated quantitatively according to the Shoulson and Fahn scale [1]. This parameter was related to the following computed tomographic measurements: the greatest distance between the frontal horns (FH), the shortest distance between the heads of the caudate nuclei (bicaudate diameter, CC) and the quotient FH/CC. The ratio of the bicaudate diameter and the external diameter of the skull across the narrowest point of the heads of the caudate nuclei (CC/OTcc) was also used as well as the bicaudate diameter and the maximum internal diameter of the skull (CC/ITmax). The best correlation was found between the bicaudate diameter and functional capacity (r = -0.64, P less than 0.05). All the quotients containing the bicaudate diameter likewise showed a correlation with functional capacity, though to a less marked degree. Thus the bicaudate diameter appears to be the most specific and simple computed tomographic parameter for the differentiation of Huntington's disease from normal states or choreatic syndromes of different origin.