On the decline and etiology of high-incidence motor system disease in West Papua (southwest New Guinea). 
The etiology of a high-incidence focus of amyotrophic lateral sclerosis and parkinsonism-dementia (ALS/P-D) in south West Papua (Irian Jaya, Indonesia), first described in the 1960s and 1970s, has been attributed to mineral deficiencies, hyperparathyroidism, and metal neurotoxicity arising from reliance on drinking water obtained from springs and shallow wells.  More recent visits (1987 and 1990) to the south West Papua focus of neurodegenerative disease cast doubt on this explanation by revealing changes in disease prevalence in communities with an unchanged water supply.  These communities have experienced a dramatic decline in ALS and a reversal in the relative prevalence of ALS and parkinsonism.  The extrapyramidal disorder can be distinguished from Parkinson disease by pyramidal features (and dementia) reminiscent of Guam P-D. Topical use of cycad seed (termed kurru) gametophyte to treat large skin lesions is advanced as a plausible but unproven etiologic factor.  Medicinal use of untreated cycad seed (Cycas sp.)  has also been linked with ALS foci in Japan (oral use) and Guam (topical use), with the additional consumption on Guam of food items prepared from Cycas sp.  seed or animals that consume cycad seed components.