Demographics

The demographic, epidemiological and electrophysiological data described in this and subsequent chapters are based on 664 patients with definite or probable amyotrophic lateral sclerosis (ALS) as defined by the El Escorial criteria (Brooks, 1994). All of the patients were examined by one of the authors (AE) between 1984 and 1996 (Table 1.1). The data are representative of typical populations of ALS patients as reported previously (Brooks, 1996). It is well established that the age-adjusted incidence of the neurodegenerative disorders (Alzheimer's disease (AD), Parkinson's disease (PD) and ALS) rises sharply with ageing and, as shown in Figure 1.1, this is true for our own data.

Gender

The overall male:female ratio of our cohort was 1.33:1. Epidemiological studies of sporadic ALS unanimously agree that the disease is more frequent in men, although the male:female ratios quoted are variable. In older patients, particularly those over 65 years, the male:female ratio begins to approach 1:1 (Chancellor et al., 1993a). Based on our own data, there is a significant negative correlation between age and the male: female ratio of ALS. This is shown in Figure 1.2, and it probably reflects the greater longevity enjoyed by women. However, this benefit is limited because of an increased risk of developing ALS. In younger patients (those less than 40 years) there is a much higher frequency of ALS amongst young men (Christensen, Hojer-Pedersen and Jensen, 1990; Strong, Hudson and Alvord, 1991; Eisen et al., 1993c).