Peripheral neuropathy associated with chronic natural killer cell lymphocytosis

We report a patient with steroid-responsive peripheral neuropathy which developed with chronic natural killer cell lymphocytosis (CNKL). A 70-year-old female with a 2-week history of progressive motor and sensory neuropathy showed a marked increase of natural killer (NK) cells in the blood, and was diagnosed as having CNKL. Nerve conduction studies (NCS) revealed a mixed axonal and demyelinating neuropathy. A sural nerve biopsy revealed infiltration of NK cells into the nerve fascicles, and demyelinating changes with axonal degeneration. The infiltrating NK cells were adjacent to myelinated fibers, showing damage of Schwann cell membrane. Treatment with oral prednisolone resulted in rapid improvement of the sensory disturbance and weakness with a significant decrease of NK cells in the blood and disappearance of the conduction blocks in NCS. This is the first case of CNKL associated neuropathy in which infiltration of NK cells was demonstrated in the nerve fascicles. Our observations suggest that the infiltrating NK cells may directly damage myelin and Schwann cells, thus causing demyelination.