One of the most common sources of symptoms in patients with MS is from lesions in the spinal cord. The spinal cord is a relatively thin band of nervous tissue that contains the pathways that allow us to feel, move, and use the bathroom. The spinal cord starts at the base of the skull where the brainstem terminates and ends in the lower back. Nerves emerge at multiple levels from the spinal cord which transmit information from the central nervous system to the peripheral nervous system. Although lesions are more common in the brain in MS- it is much bigger than the spinal cord after all- lesions in the spinal cord are much more likely to produce clinical symptoms. Patients with MS often have lesions in the brain that do not cause symptoms, but this is rarely the case with lesions in the spinal cord. Inflammation of the spinal cord in termed transverse myelitis. This term is applied to illnesses other than MS, and inflammation of the spinal cord can occur for a variety of reasons.
To understand the symptoms produced by lesions in the spinal cord, let me briefly review the anatomy of the spinal cord. Like the brain, the spinal cord is divided into gray matter and white matter. The gray matter contains neurons and cell bodies, while the white matter contains the axons than link neurons together. In the brain, the grey matter is on the outside while in the spinal cord, the grey matter forms an “H” shape inside the spinal cord when viewed from the top down, termed an axial view. The MRI below shows this pattern (the grey matter looks white and the white matter looks grey because of the MRI). The MRI below on the left is a view of the spinal cord from the axial view. On the right, the spinal cord is viewed from the side. The spinal cord is normally a solid gray color and it is surrounded by spinal fluid that is seen as white surrounding the spinal cord.
The three most important pathways in the spinal cord
1. The Corticospinal Tract: This is a descending pathway that carries motor fibers to the peripheral nerves.
2. The Dorsal Column Pathway: This is an ascending pathway that carries proprioception (the body’s sense of where it is localized in space) and fine touch sensation from peripheral nerves to the brain.
3. The Spinothalamic Tract: This is an ascending pathway that transmits pain and temperature touch sensation from peripheral nerves to the brain.
The location of these pathways is outlined in the diagram below.
In addition to these pathways, there are other pathways connect to the cerebellum to help control posture and balance. There are also pathways that allow for bowel and bladder control. In my next post, I will discuss typical presentations of spinal cord disorders in MS.