Dawson's fingers
Encyclopedia
Multiple sclerosis
Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms...
patients. The condition is supposed to be the result of inflammation or mechanical damage by blood pressurearound long axis of medular veins.
Dawson's fingers spread along, and from, large periventricular collecting veins, and are attributed to perivenular inflammation. Lesions far away from these veins are known as Steiner's splashes.
Distribution
Post-mortem authopsy reveal that gray matter demyelination occurs in the motor cortex
Motor cortex
Motor cortex is a term that describes regions of the cerebral cortex involved in the planning, control, and execution of voluntary motor functions.-Anatomy of the motor cortex :The motor cortex can be divided into four main parts:...
, cingulate gyrus, cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
, thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. Cortical lesions have been observed specially in people with SPMS but they also appear in RRMS and clinically isolated syndrome. They are more frequent in men than in women and they can partly explain cognitive deficits.
It is known that two parameters of the cortical lesions, fractional anisotropy (FA) and mean diffusivity (MD), are higher in patients than in controls. They are larger in SPMS than in RRMS and most of them remain unchanged for short follow-up periods. They do not spread into the subcortical white matter and never show gadolinium enhancement. Over a one-year period, CLs can increase their number and size in a relevant proportion of MS patients, without spreading into the subcortical white matter or showing inflammatory features similar to those of white matter lesions.
The first plausible explanation of their distribution was published by Dr. Schelling. He said:
- The specific brain plaques of multiple sclerosis can only be caused by energetic venous back-jets set in motion by intermittent rises in the pressure in the large collecting veins of the neck, but especially of the chest..
But no problems with chest veins was ever found.
Recently, it has been remarked that it can plausibly be accounted for by veno-venous reflux, according to the CCSVI theory. This results in a finger-like appearance of the lesions extending mainly off the ventricles
Ventricular system
The ventricular system is a set of structures containing cerebrospinal fluid in the brain. It is continuous with the central canal of the spinal cord.-Components:The system comprises four ventricles:* right and left lateral ventricles* third ventricle...
within the brain.
This morphologic appearance was named Dawson's fingers by Charles Lumsden, after the Scottish
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
pathologist James Walker Dawson
James Walker Dawson
Dr. James Walker Dawson was a Scottish pathologist remembered for his work on multiple sclerosis including the description of the eponymous Dawson's fingers.- Biography :...
, who first defined the condition in 1916.
Demyelination process
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
breakdown. It is a tight vascular barrier between the blood and brain that should prevent the passage of antibodies through it, but in MS patients it does not work. For unknown reasons special areas appear in the brain and spine, followed by leaks in the blood-brain barrier where immune cells infiltrate.
According to the view of most researchers, a special subset of lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s, called T helper cell
T helper cell
T helper cells are a sub-group of lymphocytes, a type of white blood cell, that play an important role in the immune system, particularly in the adaptive immune system. These cells have no cytotoxic or phagocytic activity; they cannot kill infected host cells or pathogens. Rather, they help other...
s, specifically Th1 and Th17, play a key role in the development of the lesion. Under normal circumstances, these lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
s can distinguish between self and non-self. However, in a person with MS, these cells recognize healthy parts of the central nervous system as foreign and attack them as if they were an invading virus, triggering inflammatory
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
processes and stimulating other immune cells and soluble factors like cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s and antibodies
Antibody
An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...
. Many of the myelin-recognizing T cells belong to a terminally differentiated subset called co-stimulation-independent effector-memory T cells. Recently other type of immune cells, B Cell
B cell
B cells are lymphocytes that play a large role in the humoral immune response . The principal functions of B cells are to make antibodies against antigens, perform the role of antigen-presenting cells and eventually develop into memory B cells after activation by antigen interaction...
s, have been also implicated in the pathogenesis of MS and in the degeneration of the axons.
The axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s themselves can also be damaged by the attacks. Often, the brain is able to compensate for some of this damage, due to an ability called neuroplasticity
Neuroplasticity
Neuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
. MS symptoms develop as the cumulative result of multiple lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s in the brain and spinal cord
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
. This is why symptoms can vary greatly between different individuals, depending on where their lesions occur.
Repair processes, called remyelination, also play an important role in MS. Remyelination is one of the reasons why, especially in early phases of the disease, symptoms tend to decrease or disappear temporarily. Nevertheless, nerve damage and irreversible loss of neurons occur early in MS.
The oligodendrocyte
Oligodendrocyte
Oligodendrocytes , or oligodendroglia , are a type of brain cell. They are a variety of neuroglia. Their main function is the insulation of axons in the central nervous system of some vertebrates...
s that originally formed a myelin sheath cannot completely rebuild a destroyed myelin sheath. However, the central nervous system can recruit oligodendrocyte stem cell
Stem cell
This article is about the cell type. For the medical therapy, see Stem Cell TreatmentsStem cells are biological cells found in all multicellular organisms, that can divide and differentiate into diverse specialized cell types and can self-renew to produce more stem cells...
s capable of proliferation and migration and differentiation into mature myelinating oligodendrocytes. The newly-formed myelin sheaths are thinner and often not as effective as the original ones. Repeated attacks lead to successively fewer effective remyelinations, until a scar-like plaque is built up around the damaged axons. Under laboratory conditions, stem cells are quite capable of proliferating and differentiating into remyelinating oligodendrocytes; it is therefore suspected that inflammatory conditions or axonal damage somehow inhibit stem cell proliferation and differentiation in affected areas
See also
- Pathophysiology of multiple sclerosis
- Internal cerebral veinsInternal cerebral veinsThe internal cerebral veins drain the deep parts of the hemisphere and are two in number; each is formed near the interventricular foramen by the union of the terminal and choroid veins....
- Great cerebral vein
- Circle of WillisCircle of WillisThe Circle of Willis is a circle of arteries that supply blood to the brain...
External links
- Dawson Fingers in Multiple Sclerosis http://www.mypacs.net/cases/DAWSON-FINGERS-IN-MULTIPLE-SCLEROSIS-4011233.html