[Steroid-responsive demyelinating peripheral neuropathy associated with chronic lymphoproliferative disorders of natural killer cells].

We herein report the findings of a 67-year-old woman with steroid-responsive multiple mononeuropathy associated with chronic natural killer (NK) cell lymphocytosis. The patient developed progressive, asymmetric weakness and numbness in all four extremities in the course of a three-month period. Nerve conduction studies revealed asymmetric demyelination in both the motor and sensory nerves, and a biopsy specimen of the sural nerve showed a conspicuous difference in the demyelination between the neighboring fascicles and the infiltration of NK cells in the endoneurium. We considered the multiple mononeuropathy in this patient to have been caused by NK cell infiltration in the endoneurium, and the observed asymmetry might have been due to differences in the NK cell intrusion among the fascicles. Corticosteroid administration resulted in a rapid neurological, electrophysiological and hematological improvement. The rapid clinical amelioration that was observed after corticosteroid therapy suggested that the neuropathy in this case had been mainly caused by the mechanical compression of the endoneurial NK cells or the inflammatory cytokines that had been released by them.