ALS Incidence Increasing in New Zealand Province
For unknown reasons, the incidence of amyotrophic lateral sclerosis (ALS) has increased steadily during the last 2 decades in a New Zealand province. This conclusion was reached by investigators who performed a prospective study in the country's North Canterbury region, from 1985 to 2006. Study results were published in this week's issue of Neurology.
The incidence rate of definite or probable ALS was found to increase by 3% per year, from 1.6 to 3.3 per 100,000 persons, during the course of 22 years, and could not be explained by the aging of the population. Median survival of patients from the time of symptom onset was 27.6 months and was not affected by interventions like percutaneous endoscopic gastrostomy (n = 57) or riluzole therapy (n = 7).* Survival was adversely affected by age (older than 50 years) and bulbar symptoms or male sex in older patients.
Studies in the northern hemisphere have consistently demonstrated a stable ALS incidence of 1.5-2.5 per 100,000 and a mean survival of 25-39 months from symptom onset.
Some 4000 miles northwest of New Zealand, on Guam, a very high incidence (eg, >100 per 100,000) of a malignant ALS/Parkinson-dementia complex (PDC) has long been noted in the local Chamorro population, beginning in the 1940s. The incidence of Guamanian ALS/PDC, however, has declined substantially over the years. A historically favored explanation is the reduced consumption, either directly or indirectly, of a proposed neurotoxin (beta-methylamino L-alanine) in Cycas micronesica, an indigenous "false palm" plant; however, this theory was recently considered to be "lacking in scientific merit" by Canadian investigators.
The incidence of ALS/PDC has also been observed to be unusually high on the Kii peninsula of Japan and in West Papua (New Guinea).
In related news, a multicenter, phase 3, randomized, double-blind, placebo-controlled study of 330 ALS patients showed no benefit (per manual muscle testing, tracheostomy-free survival, or functional rating) of subcutaneous human recombinant insulin-like growth factor type 1 (IGF-1).
* Only 7 patients received riluzole therapy because it is not publicly funded in New Zealand.
Photo of Rakaia River, which separates North Canterbury from Mid Canturbury in New Zealand, by Greg Hewgill at Flickr.
