Peripheral nervous system pathology in relapsing experimental allergic encephalomyelitis.

A recurrent type of primary demyelination was found in the anterior roots and dorsal root ganglia of strain 13 guinea-pigs with relapsing experimental allergic encephalomyelitis. Single nerve fibre studies revealed a predominant nodal--paranodal distribution of the destruction of myelin in these nerves. Damage of the Schwann cell--axolemmal junction was found in the majority of the abnormal nodes of Ranvier. This was accompanied by the formation of supernumerary adaxonal Schwann cell processes which further altered the normal myelinating cell--axon relationship. It is concluded that variations in antigenic composition may play a role in the selective involvement of the anterior roots. The pathogenesis of the observed nodal changes is discussed.