Topography of remyelinated chronic spinal cord lesions in herpes simplex virus type 2 infections of mice.

Six-week-old outbred mice were infected intracerebrally with a low dose of the MS strain of herpes simplex virus type 2. About 1% of neurologically abnormal survivors developed paralysis or severe leg weakness during the first three weeks of infection. Weakness persisted with little subsequent improvement. Five to 8 months later, 4 such mice were killed, and each spinal cord was examined in Epon sections in a series of transverse sections along their lengths. All cords had 2 or more major white matter lesions which were typically greatly elongated in the rostrocaudal dimension, as seen in multiple sequential sections. While a lesion's appearance frequently suggested some degree of tract association, its size, contour and position frequently varied from level to level in a manner which is not characteristic of tract degeneration. Further, axons were preserved in these lesions, and had been remyelinated. This was accomplished by a combination of oligodendrocytes and Schwann cells. The only evidence of Wallerian degeneration in these spinal cords was a modest reduction in the cross-sectional area of a white matter column associated with the most severe lesions. These pathological findings are consistent with previous ones in this model. Rostrocaudal elongation of spinal cord lesions may be seen in other animal models of virus-induced demyelination; this and other features reported here have been described in multiple sclerosis.