Multiple sclerosis prevalence among Sardinians: further evidence against the latitude gradient theory

A descriptive epidemiological survey was extended to the whole province of Sassari, northern Sardinia between latitudes 40 degrees 30' N and 41 degree s N. Results showed a crude total prevalence rate of 144.4 per 100 000 on p revalence day (31 December 1997), and an onset-adjusted prevalence rate of 149.7 per 100 000. The total average annual incidence rate was 4.9 per 100 000 for the whole time interval studied (1968-1997), having increased from 2.0 in 1968-1972 to 6.8 in the last quinquennium considered. A substantial improvement in MS case ascertainment due to the introduction of new diagnos tic procedures might account for such rates in Sardinia as well as in other Italian regions. However, when comparing our data with those obtained in t he province of Ferrara, in the same time frames (1968-1997), a nine-fold ve rsus a five-fold increase of MS prevalence was detected in Ferrara and Sass ari, respectively. MS incidence temporal trend also notably increased in Sa ssari, but remained substantially stable in Ferrara. The progressive shorte ning of the time interval between clinical onset and diagnosis, and the pro portion of benign-mild MS cases, were similar in both studies, thus suggest ing a similar diagnostic accuracy. In our opinion, the repeatedly assessed increase of MS frequency in our province, at least partially does represent an actual rise of MS risk among Sardinians, thus disproving the latitude g radient-based theory (i.e. prevalence rates correlate with geographical lat itudes) and supporting the hypothesis of a "Sardinian focus" of MS in a gen etically susceptible population.