Guamanian neurodegenerative disease: electrophysiologic findings

Amyotrophic lateral sclerosis (ALS), parkinsonism and/or dementia are highl y prevalent among the Chamorro population of Guam. The incidence of Guamani an ALS has markedly declined in recent years, but these incidence figures m ay reflect underascertainment of subclinical disease. Guamanian Chamorro pa tients have not been systematically studied using modern clinical neurophys iological techniques. Electromyography (EMG: needle exam and nerve conducti on studies) was used to study 29 patients with the major subtypes of Guaman ian neurodegenerative disease, as well as 11 neurologically normal Guamania n Chamorro subjects. Central conduction was assessed by somatosensory evoke d potentials (SEP's) in 16 patients. EMG evidence of peripheral neuropathy, (often subclinical) was found in 45% of Guamanian patients but no Chamorro control subjects. Diabetes mellitus, which is highly prevalent in this pop ulation, was present in some, but not all of these cases. Clinically unsusp ected motor neuron disease was identified by EMG in only one of the 23 Guam anian patients with parkinsonism and/or dementia and in none of the 11 Cham orro control subjects. Two of seven patients with the clinical phenotype of Guamanian ALS had a more benign EMG pattern on the needle electrode exam w ith absence of fibrillation and fasciculation potentials. Three of 16 patie nts tall with parkinsonism and dementia) had mildly abnormal tibial SEP's. No patient had EMG evidence of myopathy or a defect of neuromuscular transm ission. We conclude: (1) peripheral neuropathy may be a manifestation of Gu amanian neurodegenerative disease; (2) the declining prevalence of ALS on G uam is not associated with the development of a subclinical form of motor n euron disease; (3) the substantial overlap of Guamanian ALS with parkinsoni sm-dementia reported in prior decades is no longer apparent; (4) abnormal c entral conduction, as assessed by tibial SEP's, is present in some patients with Guamanian parkinsonism-dementia. (C) 1999 Elsevier Science B.V. All r ights reserved.