Spinal cord gray matter demyelination in multiple sclerosis-a novel pattern of residual plaque morphology

Abstract

The extent and pattern of gray matter (GM) demyelination in the spinal cord in multiple sclerosis (MS) has not been examined in detail. Human autopsy material was obtained from 36 MS cases and 12 controls. Transverse sections were taken from five levels of the spinal cord (upper cervical, lower cervical, upper thoracic, lower thoracic and lumbar levels) and the extent of GM and white matter (WM) demyelination evaluated using proteolipid protein immunohistochemistry (IHC). The proportion of the GM that was demyelinated (33%) was significantly greater than the proportion of demyelinated WM (20%) (P < 0.0001). Similarly, demyelination was more extensive in the GM than in the WM at each of the five cord levels. The extent of GM demyelination was not significantly different between the five cord levels while WM demyelination was greatest at the upper cervical level. Morphologically, the borders of a proportion of the GM plaques show a strict respect for the GM/WM boundary. We demonstrate that extensive demyelination occurs in the GM of the spinal cord in MS. Myelin protein IHC reveals a novel pattern of residual plaque morphology challenging previous work suggesting that MS plaques display a total disregard for anatomical boundaries.

Figure 1

Paraffin sections from control (A–C) and multiple sclerosis (MS) spinal cords (D–K), immunohistochemically stained with anti‐proteolipid protein antibody. A. Staining in the non‐diseased cord demonstrating a paucity of myelin in the gray matter (GM) commissure (solid box, shown at higher magnification in panel B) and the Substantia Gelatinosa (dashed box, panel C). D,E. The GM/white matter (WM) boundary (black line) and MS lesions (shaded) are outlined; this section contains one pure GM lesion and one mixed GM/WM lesion. F–K. Higher magnification images demonstrating areas of completely demyelinated GM (F), markedly reduced myelin density in the GM (G), myelinated GM (H), completely demyelinated WM (I), markedly reduced myelin density in the WM (J) and myelinated WM (K). The scale bars in B and C represent 500 µm; in F–K they represent 50 µm.

Figure 2

Bar chart of proportion of gray matter (GM) and white matter (WM) that is demyelinated at different levels of the spinal cord. UC = upper cervical; LC = lower cervical; UT = upper thoracic; LT = lower thoracic; Lum = lumbar. Values represent mean ± standard error.

Figure 3

Paraffin sections from multiple sclerosis (MS) spinal cords stained with anti‐proteolipid protein (PLP) antibodies (A–E, H–J) and Luxol fast blue (LFB) (F, G, K). A–C. Many MS plaques show a similar morphology to those described previously using conventional staining techniques. The principal predilection sites for white matter (WM) plaques are the central portion of the posterior columns (A) and wedge‐shaped plaques in the lateral columns which frequently extend laterally to the pial surface of the cord and medially to the gray matter (GM), displaying a complete disregard for the GM/WM boundary (B). C. In a number of cases lesions show a striking symmetry about the midline. A proportion of mixed GM/WM (D,F) and pure GM lesions (H,J,K) appear to “expand” within the GM while maintaining a strict respect for the GM/WM boundary. D,F. Lesion morphology demonstrated using both PLP‐ and LFB‐staining. E,G. Higher magnification images from panels D and F (boxes) demonstrate complete demyelination of the GM commissure with sparing of the adjacent WM. H. Lesion involving the entire right anterior horn, respecting the GM/WM boundary, and extending to the contra‐lateral GM horn via the GM commissure. I. High magnification image from panel H (box). J,K. The GM lesion on the left respects the GM/WM boundary. The dashed lines represent the GM/WM boundaries. Scale bars (E, G, I) represent 150 µm.

Figure 4

Paraffin sections from MS spinal cords stained with anti‐proteolipid protein (PLP) antibodies (A,C,E,G,I) alongside adjacent sections stained with Luxol fast blue (B,D,F,H,J respectively). Lesion morphology is more readily appreciated using immunohistochemistry, with the PLP‐stained sections demonstrating greater contrast between the myelinated and demyelinated gray matter (GM). C,D. Higher magnification images from panels A and B (boxes). E,F. Pure GM plaque, also shown at high magnification (G,H). I,J. Demyelination of the GM commissure is more clearly delineated using PLP‐staining. Scale bars (C,D,G,H) represent 500 µm.