PERIPHERAL NERVOUS-SYSTEM INVOLVEMENT IN HUMAN AND EXPERIMENTAL CHRONIC AMERICAN TRYPANOSOMIASIS

An electrophysiological and histological study of the muscle and the p eripheral nervous system (PNS) was carried out in chronic human Americ an trypanosomiasis (Chagas' disease) and in an experimental Chagas' di sease (Chd) mouse model. Altogether 995 patients with chronic Chd and 261 mice, experimentally infected with RA and CA-I parasite strains, w ere investigated. Results were compared with matched controls. Techniq ues employed in humans were: clinical assessment, conventional electro myography (EMG), estimated number of motor units, motor and sensory ne rve conduction velocities, repetitive nerve stimulation and muscle and sural nerve biopsies. In mice conventional EMG, sciatic nerve conduct ion time, sciatic nerve action potential amplitude, in vitro miniature end-plate potentials (MEPPs) and end-plate potentials (EPPs) recordin gs, muscle, nerve and spinal cord histology and identification of cell phenotypes within the inflammatory infiltrates were the employed proc edures. Out of 511 patients submitted to clinical examination, 52 disc losed signs and symptoms of mixed peripheral neuropathy. By employing electrophysiological techniques, it could be shown that about 30 % of the investigated patients had one or more of the following features. d iminished interference pattern, most of the remainder motor unit poten tials being (MUPs) polyphasic; reduced number of functional motor unit s in the thenar, hypothenar, soleus and/or edb muscles, slow sensory a nd motor nerve conduction velocities; low sensory action potential amp litude and impairement of neuromuscular transmission. In mice, MUPs du ration and amplitude were increased at later stages of the infection, nerve conduction was slow, nerve action potentials were of low amplitu de, mepps were of low amplitude and double epps were frequently found. Muscle histology in humans with chronic Chd showed type I and type II grouping, atrophic angular fibers and targetoid muscle fibers. In mic e perivascular mononuclear cells infiltrates, small round fibers, musc le fibers necrosis, atrophic angular fibers, type II muscle fibers gro uping and grouped muscle fibers atrophy were found. Sural nerve sample s showed segmental and paranodal demyelination and axonal loss. The sa me features were observed in mice nerves, also in this model mononucle ar cells infiltrates at the nerve, dorsal root ganglia and meninges su rrounding the spinal cord were observed. Muscle and nervous tissues in filtrates were mainly composed of T lymphocytes with predominance of C D8 or CD4 subsets according to the parasites strain employed for infec ting the animals. These findings suggest that the skeletal muscle and the PNS may be involved in chronic american trypanosomiasis.