Neuromyelitis optica with intraspinal expansion of Schwann cell remyelination

We report a case of neuromyelitis optica (NMO) with an unusual pattern of remyelination in the spinal cord. A Japanese woman complained of pain and numbness in the left thumb at the age of 36 years. She mainly presented with optic and spinal symptoms and was initially diagnosed as multiple sclerosis (MS). Her bilateral eyesight decreased, which led to light perception only in the right eye. She became unable to walk without a wheelchair. In spite of steroid pulse therapy, plasma exchange therapy and immunosuppressive therapy, her symptoms gradually worsened. After 33 years of a relapsing-remitting course, she died of septic urinary tract infection at the age of 69 years. Autopsy revealed prominent demyelination in the optic tract and the spinal cord. The optic nerve showed extensive demyelination accompanied by axon depletion. The spinal cord lesions were found in C8 to L2 level (contiguous 15 segments), especially Th5 to Th11 level. The thoracic spinal cord showed extensive remyelination spreading from the entry zone of peripheral nerves to the central portion. Regenerative myelin showed immunopositivity for Schwann/2E, a marker of Schwann cells and myelin of the peripheral nervous system. Expressions of glial fibrillary acidic protein and aquaporin 4 (AQP4) were weakened in the area of Schwann cell remyelination, suggesting that the essential pathogenesis of this case was disturbance of astrocytes. Inhibition of gliosis probably led to cystic cavities, and destruction of basal lamina may have permitted Schwann cells of peripheral nerves to enter the spinal cord and proliferate within empty spaces. Compared with the optic tract and the spinal cord lesions, a large part of the brain plaques was vague and inactive. We pathologically diagnosed this case as NMO for optic neuritis, myelitis, a contiguous spinal cord lesion and loss or decrease of AQP4 expression.